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Commercial Production of

Greenhouse Tomatoes

Agriculture Handbook No. 382

X

Agricultural Research Service

UNITED STATES DEPARTMENT OF AGRICULTURE
PRECAUTIONS

Pesticides used improperly can be injurious

to man, animals, and plants. Follow the directions and heed all precautions on the labels.

Store pesticides in original containers under

lock and key—out of the reach of children

and animals—and away from food and feed.

Apply pesticides so that they do not endanger humans, livestock, crops, beneficial insects,

fish, and wildlife. Do not apply pesticides when

there is danger of drift, when honey bees or

other pollinating insects are visiting plants, or

in ways that may contaminate water or leave

illegal residues.

Avoid prolonged inhalation of pesticide

sprays or dusts; wear protective clothing and

equipment if specified on the container.

If your hands become contaminated with a

pesticide, do not eat or drink until you have

washed. In case a pesticide is swallowed or

gets in the eyes, follow the first aid treatment

given on the label, and get prompt medical attention. If a pesticide is spilled on your skin or

clothing, remove clothing immediately and

wash skin thoroughly.

Do not clean spray equipment or dump excess spray material near ponds, streams, or

wells. Because it is difficult to remove all traces

of herbicides from equipment, do not use the

same equipment for insecticides or fungicides

that you use for herbicides.

Dispose of empty pesticide containers

promptly. Have them buried at a sanitary

land-fill dump, or crush and bury them in a

level, isolated place.

NOTE : Some States have restrictions on the

use of certain pesticides. Check your State and

local regulations. Also, because registrations of

pesticides are under constant review by the

U.S. Department of Agriculture, consult your

county agricultural agent or State Extension

specialist to be sure the intended use is still

registered.

FOU.OW TMK LABKU ^

U.S. »trARTMIIIT OF ACdCUlIUK

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CONTENTS

Page

Locating a commercial greenhouse 1

Types of greenhouses 2

Glass 2

Plastic film 4

Rigid vinyl or fiberglass 5

Cultural techniques 5

Ground beds 5

Trough culture 7

Ring culture 7

Hydroponics 7

Plant nutrition and fertilization 8

Fertilizers 8

Fertilization programs 9

Deficiency symptoms 9

Cropping plans 10

Varieties of greenhouse tomatoes 11

Starting the planting stock 13

Number of seeds and plants needed _ _ 13

Time for sowing seed 13

Seeding 14

Page

Growing the transplants . _ 16

Preparing for planting 18

Planting 19

Mulching 20

Temperature and humidity control 20

Training and pruning 22

Watering 24

Carbon dioxide enrichment 25

Pollination 27

Mechanical methods 27

Chemical treatments 28

Diseases 29

Nematodes 29

Insects 30

Yields 30

Harvesting 30

Grading, packing and marketing 32

Washington, D.C. Issued January 1971

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

Price 30 cents

IV
T COMMERCIAL PRODUCTION

OF GREENHOUSE TOMATOES\ v

-^

By ALL^ K. STONER, Horticulturist, Crops Research Division, Agricultural Research Service, U.S.

éT 'í< of Agriculture

Department

Tomato production in greenhouses is one of

the most technical and intensive of agricultural enterprises. It can be very profitable if

the available technical information and the

many facets of the science of growing greenhouse tomatoes are thoroughly understood and

practiced.

Greenhouse culture permits winter tomato

production, and provides the opportunity for

precise control of plant growth by regulating

soil moisture, soil fertility, temperature, humidity, and other factors.

A greenhouse grower should have a thorough

understanding of how the basic factors of sunlight, temperature, water, carbon dioxide, and

nutrition affect plant growth. He should also

learn about the diseases and pests that aifect

greenhouse tomatoes to be able to anticipate

trouble and to control it. A successful greenhouse operator must also be a good businessman. He needs to keep accurate production

records and to know marketing practices. In

addition, a greenhouse grower should understand the plumbing, mechanical, electrical, and

heating equipment used. Finally, and perhaps

most difiicult of all, a greenhouse operator must

learn to apply to practical situations the technical information available to him. This can be

learned only through actual experience in

greenhouse culture.

In recent years the volume of greenhousegrown tomatoes has increased steadily in this

country. The increase is attributed partly to the

development of plastic and fiberglass materials

that can be used in greenhouse construction.

Greenhouses covered with these materials

are less expensive to build than those covered

with glass.

Nearly every State has some commercial

greenhouse tomato production. In 1966, Ohio

led with about 600 acres of tomatoes under

glass or plastic. Indiana had about 100 acres;

and Massachusetts, Michigan, Illinois, New

York, Texas, and Missouri each had more than

25 acres. Although tomato greenhouses are

widely scattered, the largest concentrations are

near the following cities: Cleveland, Boston,

Indianapolis, Cincinnati, Toledo, Terre Haute,

Grand Rapids, Kansas City, and Rochester.

LOCATING A COMMERCIAL GREENHOUSE

Several factors should be considered when

selecting a site for a greenhouse. Proximity to

a good market is of prime importance. Growing tomatoes close to the market saves transportation expense and reduces transit time,

thereby helping the grower to market the

highest quality, vine-ripened product.

* This Agriculture Handbook supersedes Farmers'

Bulletin 2082, "Commercial Production of Greenhouse

Tomatoes."

The area selected should have a high percentage of sunshine during the fall and winter

days if a fall tomato crop is to be grown. It is

possible, however, to grow tomatoes successfully in areas subject to much cloudy weather.

A site fully exposed to sunlight, but protected

from winds and storms by windbreaks, will

save fuel and greenhouse maintenance costs.

Greenhouses should also be situated close to

adequate supplies of fuel, good water, and
AGRICULTURE HANDBOOK NO. 382, U.S. DEPT. OF AGRICULTURE

power. If natural gas is readily available at a

relatively low cost, it is usually the cleanest

and most economical fuel. When natural gas is

not available, fuel oil, coal, or electricity must

be used. Since large quantities of water are required to grow a tomato crop, an adequate supply of good-quality water is particularly important.

Greenhouses for tomato production should be

built on sites with a fertile, medium-textured,

well-drained soil. An area with a high water

table should be avoided. The site should also

have good air drainage to prevent polluted and

moisture-laden air from persisting around the

greenhouse. Moist air encourages the development of foliage diseases. The extent of air-pollution damage to tomatoes is not known, but an

area free from smoke and gases is recommended. It is known that gases such as sulfur

dioxide and carbon monoxide damage tomato

plants when present in sufficient quantities.

Land for greenhouses should be carefully

graded and leveled. This is important for

maintaining uniform temperature and humidity throughout the greenhouse. Pockets of cool

air or high humidity may develop when the

site is not level.

A plentiful supply of dependable labor is

especially important, because of the large

amount of hand labor required in growing

greenhouse tomatoes. Also, consideration

should be given to the possibility of future expansion. If expansion is anticipated or even remotely possible, adequate space should be set

aside and the original house built so that additional construction is convenient.

The orientation of a greenhouse has little effect on growing tomatoes in this country. A

north-south direction provides a more uniform

distribution of light throughout the year and

enables the construction of headhouses at the

north end of the range. Greenhouses constructed in an east-west direction with the crop

rows running north and south provide the best

exposure to sunlight during short winter days.

TYPES OF GREENHOUSES

Greenhouses for tomato production may be

covered with three basic types of material : (1)

Glass; (2) soft, pliable plastic films; or (3)

rigid plastic or fiberglass. Tomatoes can be

grown equally well in houses covered with any

of these materials, although management practices may vary somewhat. For example, plastic

houses are usually more nearly airtight than

glass houses, therefore, ventilation may be

more critical. The relative cost of the materials, the prevailing environmental conditions,

the anticipated life expectancy of the structure, and the personal preferences of the grower will determine the type of greenhouse to be

constructed.

Glass

Glass-covered greenhouses are the most durable of all types. They are less subject to damage from high winds and heavy snow loads

than most plastic greenhouses. Glass greenhouses are considered permanent structures

with permanent walks, heating systems, and

other internal features. Since they are permanent, they can be insured. In some respects,

growing tomatoes in a glass house may require

less exacting management than growing them

in plastic greenhouses.

High initial cost is the primary disadvantage

of a glass greenhouse. Also, as permanent

structures, they usually have a higher tax assessment than plastic greenhouses. Another

disadvantage of glass houses is that they are

subject to damage from hail or rocks. In areas

where hailstorms are common, glass houses are

not recommended.

Glass greenhouses for tomato production are

usually constructed with truss-supported, even-spanned roofs. An example of such

houses is shown in figure 1. Where more than

one house is used, they may be built separate

or as ridge-and-furrow houses. Ridge-andfurrow houses are two or more even-span

houses built together. The inner gutters may

or may not have side walls. Uneven-span and

lean-to greenhouses are used occasionally.

The frame of a glass house may be constructed of wood, steel, or aluminum. Older

greenhouses usually have wooden rafters and
COMMERCIAL PRODUCTION OF GREENHOUSE TOMATOES

BN-36631

FIGURE 1.—A range of glass greenhouses used for

tomato production.

steel purlins and posts. Aluminum has replaced

steel and wood in most new greenhouses because it is lighter in weight and requires no

maintenance. Wooden and steel parts require

repainting about every 3 years on the outside

and every 7 years on the inside. Another trend

in greenhouse construction is to use wider rafter spacing and therefore wider glass panes. In

older houses, 18-inch glass was standard, but

24-inch glass is now common. Wider rafter

spacing allows more light to enter the greenhouse.

The size of a greenhouse may range from a

few hundred square feet to more than an acre.

The primary consideration should be for its

proper management and the convenience of

working in the house. For example, if tomato

rows exceed 100 feet in length, harvesting may

be inefficient because baskets of fruit must be

carried long distances. The greenhouse should

be 8 to 8-1/2 feet tall at the sides to allow ample

growing room for tomato plants. For more specific details on greenhouse construction, one

should contact a supplier of commercial greenhouses.

Internally, greenhouses are usually empty of

benches or other obstructions, because tomatoes are most commonly grown in groundlevel beds. In the past, raised benches were

used somewhat, but their use has declined primarily for economic reasons. Ground beds can

be more easily prepared with power equipment

and, because tomatoes grow 6 feet or more in

height, they are easier to train, prune, pollinate, and harvest in ground-level beds. Certain

growing techniques do require troughs or

tanks, and these are described in the section on

Cultural techniques.

Practically all glass greenhouses are heated

by a central steam or hot-water boiler system.

The steam may also be used to sterilize the

plant beds, fiats, and equipment. Small greenhouses, or those in areas where little heat is

required, may use natural-gas or fuel-oil heaters or furnaces. With such heaters, provision

must be made to circulate the warm air to

maintain uniform temperature throughout the

house. Fans or perforated plastic tubes running the length of the greenhouse may be used

to distribute the warm air.

To prevent buildup of high humidity, which

encourages disease epidemics, and to control

high temperature, greenhouses must have adequate ventilation. Permanent glass houses usually have ventilators in the sides and/or ridges.

Sometimes large, perforated plastic tubes like

those used for distributing heat are suspended

in the greenhouse and used for ventilation. A

fan at one end of the tube pulls the air into the

tube through the perforations and then

through the length of the tube and out the end

of the greenhouse.

Many greenhouses are equipped with heating and ventilation equipment designed to be

controlled automatically or manually. Also,

some growers devise or purchase systems with

which the temperature and humidity at various points in the greenhouse can be monitored

and adjusted from a single location. Such sophisticated equipment aids the grower in maintaining precise control over his crop and frees

him for other tasks.

In areas where high fall and spring temperatures are common, such as the Southwest,

forced cooling may be needed for satisfactory

yields of high-quality fruit. The most satisfactory and economical system for cooling greenhouses is the fan-and-wet-pad system, which

works by evaporative cooling. With this system, it is possible to reduce the temperature by

about 80 percent of the difference between

wet-bulb and dry-bulb temperature readings.

The fan-and-pad system uses a series of

wood-fiber pads installed vertically on one side
AGRICULTURE HANDBOOK NO. 382, U.S. DEPT. OF AGRICULTURE

of the greenhouse and large exhaust fans on

the opposite side. The exhaust fans draw air

through the pads, which are kept wet by continually circulating water. The moist air coming through the pads is cooled by evaporation

of the water.

A common method of watering is overhead

sprinkling, using a permanent system of overhead pipes and nozzles. The primary advantage

of this method is that the pipes do not interfere with soil preparation, planting, and other

operations. Also, large areas can be watered at

one time. A serious disadvantage of overhead

watering is that the plant foliage becomes wet,

and this creates conditions favorable for the

development of diseases such as leaf

mold.

Surface or near-surface watering is also

widely used. This may be done by a system

of perforated pipes or hoses on the soil surface

or by sprinkler pipes 6 to 12 inches above the

soil surface. Such a system may be made permanent or temporary. This system has the advantage of not wetting the foliage. However,

the arrangement of the pipes may interfere

with soil preparation and other necessary operations. Another variation of surface watering

is the use of hoses to water individual plants.

This is used primarily when plants have recently been transplanted into the beds. Watering with a hose involves much labor and is

most practical in small greenhouses.

The least common watering system is subirrigation. Watering by this method is through a

system of 3- or 4-inch drainage tiles laid endto-end with about one-quarter inch between

pieces. The tiles are buried below plow depth

and spaced from 2 to 4 feet apart. The ends of

the tile lines are left open so water can be conducted into them by garden hose or permanent

water pipes. A disadvantage of this system is

that the tiles may become clogged and no

longer permit water movement through them.

Plastic Film

Greenhouses covered with plastic film can

generally be constructed for one-third or less

of the cost of a glass greenhouse. This makes

plastic greenhouses popular with growers

who are just getting established and do not

have the resources necessary to construct a

conventional glass house.

Plastic greenhouses usually have wooden or

metal pipe frames. They may be of any of several designs (fig. 2). They are usually built as

temporary structures, designed to last only a

few years, and therefore maintenance costs are

high. Usually, plastic greenhouses have a

lower tax assessment than glass greenhouses,

because they are only temporary structures.

FIGURE 2.—A small plastic greenhouse.

BN-36543
COMMERCIAL PRODUCTION OF GREENHOUSE TOMATOES

Plastic films suited for greenhouse construction are polyethylene, polyvinyl chloride, and

polyester. Polyethylene film is the least expensive material and the least durable. When used

as a greenhouse covering, it can be expected to

last only one winter. Vinyl films are more expensive than polyethylene, but they may last

up to 4 years. Disadvantages of vinyl materials

are their attraction for dirt and dust from the

air and their tendency to expand and contract

with temperature changes. Polyester film is

slightly more expensive than vinyl and may

have a useful life of 2 to 5 years. Several State

agricultural experiment stations have bulletins

available that discuss in detail various plastic

materials and their use in greenhouse construction.

Plastic greenhouses may be of several different designs, including A-frame, scissorstruss, truss-rafters, center-post, rigid-frame,

gothic-arch, quonset, panel, ridge-and-furrow,

and air-supported houses. Whichever design is

used, consideration should be given to maximum light penetration, easy ventilation, and

adequate heating.

On the inside, plastic greenhouses for tomato

production are quite similar to glass houses.

The type of heating system best suited for a

greenhouse depends on the size and design of

the house and the climate of the area where

the greenhouse is located. The heating system

must be able to maintain a minimum temperature of 60° F. on the coldest nights and must

release no toxic gases into the greenhouse.

Heaters used in plastic greenhouses include

temporary convection-type heaters or space

heaters, unit heaters installed in the peak of

the house, forced warm-air furnaces, and

steam or hot-water boilers. For large greenhouses, a boiler system is probably best. However, for smaller greenhouses the first three

types are usually preferred. Liquified petroleum (LP) gas, oil, or natural gas can be used

as fuels for heating plastic houses. It is very important that all heaters and furnaces be vented

to the outside. During combustion of the fuel,

fumes are released that may injure the plants

in the greenhouse.

Ventilation of plastic greenhouses may be by

ridge or side ventilators, removable panels, or

by exhaust fans installed in the sides or ends

of the house. Designing a plastic house with

ventilators complicates construction and makes

the house more expensive. Thermostat-controlled fans are the easiest way to ventilate.

The fans should be large enough to provide a

complete exchange of air every 1 to I-I/2 minutes, as is necessary during warm weather.

Ventilation tubes as described for glass

houses are particularly good for ventilating

plastic houses during cold weather. With such

tubes, cold outside air is brought in through

the tube suspended in the peak of the greenhouse and not directly onto the plants. The

fresh air mixes with the inside air without

causing cold drafts on the plants.

Watering in plastic greenhouses is generally

by hose or by some temporary soil-surface system.

Rigid Vinyl or Fiberglass

Greenhouses covered with rigid panels of polyvinyl chloride (PVC) or fiberglass are satisfactory for tomato production. The durability

of these materials may range from 2 to 20

years, depending on the quality. PVC panels

and cheaper grades of fiberglass may discolor

so badly that they no longer allow satisfactory

plant growth. PVC is also quite susceptible to

hail damage and should not be used in areas

where hailstorms are common. A serious peril

of fiberglass is its susceptibility to fire.

The rigid materials are usually used on permanent structures, and may be as expensive to

build as a glass greenhouse. The frame, heating, ventilation, and watering for such a house

are similar to those discussed for glass greenhouses.

CULTURAL TECHNIQUES

Ground Beds

Greenhouse tomatoes are most commonly

grown in ground beds (fig. 3). Ground beds can

be easily prepared with power equipment.

Since tomatoes grow 6 feet or more in height,

it is easy to train, prune, pollinate, and harvest
AGRICULTURE HANDBOOK NO. 382, U.S. DEPT. OF AGRICULTURE

BN-86624

FIGURE 3.—Greenhouse tomato plants growing in a

soil bed.

them when they are grown in ground-level

beds.

The primary disadvantage of growing in

ground beds is the difficulty in controlling soilborne diseases. Even in greenhouses equipped

with permanent steam tile for sterilization, it

is not possible to steam deeply enough to kill

all disease-producing organisms. Also, sterilizing greenhouse beds is expensive.

Production potential in ground beds is limited if a greenhouse is built on a site with poor

soil. The soil should have good physical properties and an initially high level of fertility. If

the greenhouse soil does not possess desirable

properties, it can be improved with certain

practices. Continuous efforts are necessary to

maintain even an initially good soil.

A greenhouse soil for tomato production

should possess good drainage and physical

properties so it will retain moisture well, but

will not become waterlogged and lack aeration.

Such a soil allows the good root growth that is

essential for good yields.

Loam to silt-loam ftoils are favored over

heavier or lighter soils. Loam soils retain moisture, yet drain well enough to allow good aeration. Heavy clay soils hold water too tenaciously, but sandy and gravelly soils do not

hold enough water. Without proper water

management, plants growing on light sandy

soils may be subjected to moisture stress that

may cause blossom-end rot. On the other

hand, overfertilization and salt accumulation

are not likely to be serious problems on light

soils, since the soil can easily be leached with

heavy waterings. Heavy soils require closer

management of fertilization practices, since

they cannot bè leached readily.

Greenhouse soils lacking desirable physical

properties can be improved by incorporating

organic material into them, or additional soil

can be brought in from the outside to build up

above the natural grade. Manure, if available,

is a good source of organic matter, as are the

organic mulches commonly used as ground covers when growing greenhouse tomatoes. These

materials are incorporated into the soil before

planting and allowed to decompose. Fine-textured soils require more organic matter than

coarse-textured soils to keep them loose and

friable.

The depth of a greenhouse soil is important,

because tomato roots may penetrate as deeply

as 6 feet. When a clay hardpan lies near the

surface, root growth is restricted and water

drainage is prevented. A natural water table

close to the surface is also undesirable. The

grower can no longer control a plant's growth

by adding or withholding water after its roots

grow into permanent water.

The nutritional level of soil can be determined by soil tests. These should be made at

regular intervals during the growth of each

crop. Deficiencies are corrected by the addition

of appropriate chemical fertilizers. Soils with

initially high fertility levels must be fertilized

periodically, because tomatoes remove large

amounts of nutrients from the soil. Chemical

fertilizer programs and soil testing will be discussed in more detail in the section on Plant

Nutrition and Fertilization.
COMMERCIAL PRODUCTION OF GREENHOUSE TOMATOES

A greenhouse soil for tomatoes should be

slightly acid, with a pH of 6.0 to 6.7. Again, a

soil test is necessary to determine the acidity

of the soil. If the soil is too acid and lime must

be added, dolomitic limestone should be used

instead of calcitic limestone to supply magnesium to the soil. Limestone should be spread

before the soil is prepared and should be

worked in thoroughly during preparation.

Trough Culture

Trough culture is a system of growing tomatoes in a trough containing natural soil or an

artificial medium. The troughs or trenches may

be scooped out of greenhouse beds or constructed with lumber and lined with plastic

film.

The troughs are filled with 4 to 6 inches of

soil or an artificial soil mix such as vermiculite

and sphagnum peat moss, and plants are

planted directly into the soil. Some plant nutrients are available from the soil initially, but

most of the nutrients must be supplied periodically in water solution.

The primary advantage of trough culture is

that complete sterilization is possible, therefore, fewer problems with plant diseases are

encountered. The plastic film lining the

troughs restricts the plant roots to the disease-free soil in the trough. Restriction of root

growth also permits better management of

early plant growth. Trough culture also allows

for complete control of the nutrient supply to

the plants and the water drainage.

A disadvantage of this system is the initial

cost of constructing the troughs and periodically replacing the soil. If an artificial soil mix

is used, it may be reused for several seasons if

it is sterilized after each crop.

Ring Culture

Ring culture is similar to trough culture except that the plants are planted into a bottomless pot or "ring" containing soil or growing

medium (fig. 4). The "ring" of soil is set on a

bed or trough like those described in the previous paragraphs. Plants grown in ring culture

are able to obtain nutrients and water from

both the soil in the ring and the underlying soil.

è^.^ ' i^'\äi' < '-^"v." '

BN-36628

FIGURE 4.—Greenhouse tomato plants growing in ring

culture.

The rings may be made of clear or black polyethylene or roofing paper. Polyethylene

rings, specifically for tomato growing, can be

purchased.

Ring culture has the same disadvantage of

initial cost as trough culture, plus the added

expense of buying the rings and the labor required to prepare them.

Hydroponics

Hydroponic culture is a system of growing

plants without soil. The plant roots are anchored in sand, gravel, or some other relatively

inert medium. All nutrients are supplied in

water solution. Except that no soil is used, and

all plant nutrients must be provided, hydroponic growing is essentially like growing by

any other technique. With proper management,

the yield and quality of fruit produced by hydroponics will be similar to that obtained with

soil culture.

The primary advantage of hydroponic culture is that it can be used where soil is lacking

or is unsuitable for plant growth. Other advantages are the exact nutritional control that is
8 AGRICULTURE HANDBOOK NO. 382, U.S. DEPT. OF AGRICULTURE

possible and the decreased chance of encountering soilborne diseases.

The initial cost of a hydroponic greenhouse

is high, because beds, tanks, and pumps are required in addition to the structure itself. Also,

this equipment must be maintained. Hydroponic culture does eliminate tillage and mulching, but it is still necessary to sterilize the beds

and gravel. Precise control of pH and proper

timing of the addition of nutrients is critical

with this system and must be closely supervised and managed.

PLANT NUTRITION AND FERTILIZATION

Greenhouse grov^ers in the past relied primarily on animal manure to supply the essential mineral elements needed for plant grovs^th.

Today growers must depend almost entirely on

chemical fertilizers. Enough fertilizer must be

used to provide plant nutrients for a maximum

crop without carrying over excessive amounts

to the next crop. Excess fertilizer in the soil

can interfere with tomato plant growth and

fruiting. The three major elements required

for plant growth are nitrogen, phosphorus, and

potassium. Other elements required in very

small amounts are iron, magnesium, manganese, boron, calcium, copper, molybdenum,

sulfur, chlorine, and zinc. These essential elements must be available to the plants regardless of the cultural technique being employed.

The pH or acidity of the soil, or the nutrient

solution in hydroponic systems, is very important to plant growth. A pH value between 6.0

and 6.7 is considered most favorable for the

growth of tomato plants. The pH values range

from 0 to 14. A neutral soil has a pH of 7.0.

Values below 7.0 indicate acidity, and values

above 7.0 indicate alkalinity.

When soil becomes too acid, the phosphorus

in it may be changed to a more insoluble form,

the compounds that supply calcium and magnesium may be deficient, and the nitrogen-fixing

bacteria in the soil may fail to thrive. On the

other hand, when the soil is too alkaline the

phosphorus changes to another insoluble form,

the nitrogen-fixing bacteria do not thrive, and

the compounds that supply potassium, manganese, iron, and boron form insoluble substances.

To determine the nutrient levels and the pH

of soil, laboratory tests must be conducted. All

State agricultural experiment stations except

California and Illinois provide soil-testing services for residents of the State. Some States

also provide plant-tissue testing services. Along

with the test results, interpretations of results

and suggestions for corrective measures are

usually provided. Many commercial laboratories and fertilizer companies also run soil and

tissue tests. In addition, kits are available that

allow the grower to make his own soil analysis

and to analyze plant tissue for nitrogen content. These kits are simple to use and can be

valuable tools if the user learns to interpret

the test results correctly.

Fertilizers

A crop of tomatoes that yields 75 tons of

fruit per acre can be expected to remove from

the soil approximately the following amounts

of nutrients per acre: Nitrogen 250 to 350

pounds; potassium 550 to 700 pounds; phosphorus 75 to 150 pounds; calcium 250 to 300

pounds; and magnesium 50 to 75 pounds.

Minor elements are removed in smaller quantities.

Many types of fertilizers are available for

greenhouse use. These include materials that

contain all three of the major elements in various ratios. Examples of commonly used fertilizers are 10-52-17, 5-10-10, 10-10-10,

15-15-15, 20-20-20. In these designations, the

first number indicates the percentage of nitrogen, the second of available phosphoric acid,

and the third of water-soluble potassium.

These fertilizers are available in both watersoluble and dry forms.

Some fertilizers supply only 1 or 2 of the

major elements. Some nitrogen supplements

and their grade are ammonium nitrate 33-0-0,

calcium nitrate 15-0-0, sodium nitrate 15-0-0,

and urea 45-0-0. Phosphorus supplements are

monoammonium phosphate 11-48-0 and diammonium phosphate 21-53-0. Potassium supple-
COMMERCIAL PRODUCTION OF GREENHOUSE TOMATOES

merits are muriate of potash 0-0-60, sulfate of

potash 0-0-48, and potassium nitrate 13-0-44.

The essential minor elements required are

usually present in soil in sufficient quantities

but may be deficient in some soils. Commercial

fertilizers containing a mixture of all of the

necessary trace elements are available for application to the soil or as foliar sprays. Many of

the fertilizers for supplying the three major

elements also have the trace elements added.

Fertilization Programs

Some growers prefer to establish a routine

fertilization schedule in their greenhouses. Periodic soil or tissue analyses are made to check

on the adequacy of the program. Others rely

more heavily on soil and tissue tests and fertilize only when the tests indicate a need for a

particular element. In these greenhouses,

samples for analysis may be taken at weekly or

biweekly intervals.

In developing a fertilization program, the

soil type, the use of manure and mulches, and

the cropping plan should be considered. A routine fertilization schedule is usually planned so

that the phosphorus and potassium are applied

in the summer or at the time of soil preparation. Nitrogen fertilizer is then applied only as

it is needed by the growing plants. Growers

who fertilize only when soil or tissue tests indicate a need for certain elements often use

water-soluble fertilizers and apply them with

the irrigation water. Soluble fertilizer is usually used also by hydroponic and trough-culture

growers.

For a routine fertilization program, one recommended schedule for 1,000 square feet is 25

to 45 pounds of 0-20-20 applied before a fall

crop and 15 to 25 pounds of 0-20-20 applied

before a spring crop. Phosphorus may also be

added as 46-percent triple superphosphate at a

rate of 10 to 15 pounds per 1,000 square feet of

bed or as 20-percent superphosphate at 25 to

30 pounds per 1,000 square feet. Potassium can

be added as potassium sulfate at a rate of 20 to

25 pounds per 1,000 square feet of bed. Ammonium nitrate, sodium nitrate, calcium nitrate, and potassium nitrate are used for sidedressing to supply nitrogen throughout the

season. Plant tissue tests may be used to determine when nitrogen fertilization is needed.

Waiting until visual symptoms are apparent to

detect deficiencies will reduce yields. It also requires experience since several elements have

similar deficiency symptoms.

The number of supplemental applications of

nitrogen fertilizer depends partly on the

amount of organic matter in the soil. Growers

who follow a schedule usually make the first

application as soon as three fruit clusters have

set. Usually two to three applications of 6 to 7

pounds of sodium nitrate or 3.5 pounds of ammonium nitrate per 1,000 square feet of bed

are enough for a spring tomato crop. For a fall

crop, one application of nitrogen fertilizer is

usually enough.

One of the most common mistakes made by

greenhouse growers is excessive nitrogen fertilization. This causes the plants to grow too

large and vegetative, and fruit set is poor. Excess nitrogen is particularly serious during November, December, and January when the days

are short and often cloudy. Excessive nitrogen

may also carry over from crop to crop. Nitrogen carryover may be reduced by plowing several tons per acre, of undecayed cellulose material into the soil before planting another crop.

Crushed corncobs or weathered sawdust may

be used for this purpose.

Deficiency Symptoms

As a supplement to soil and foliar analysis,

visual recognition of deficiency symptoms may

be important. Deficiency symptoms are given

below for the essential elements required for

plant growth :

Nitrogen—Slow stunted growth; leaves becoming pale green, then yellow, especially the

older leaves ; reduced fruit size.

Phosphorus.—Slow growth; slender stems;

dull purple color on leaf blades and stems,

especially on the underside; delayed maturity.

Potassium,—Curling, bronzing, and dying of

leaf margins, especially the older leaves; some

brown spots throughout the leaves ; uneven ripening of fruit, inside of fruit not solid.

Calcium.—Death of growing point and dieback of main stem ; new leaves chlorotic while

old leaves remain green; new growth not turgid ; fruit breakdown at blossom end.
10 AGRICULTURE HANDBOOK NO. 382, U.S. DEPT. OF AGRICULTURE

Magnesium.—Chlorosis between veins of old

leaves while veins remain green; chlorotic

areas turning brown and dying.

Iron^.—Young leaves developing light-yellow

color, first between the veins and later over the

entire leaf ; usually no death of tissue.

Manganese.—Chlorosis, first between veins

of new leaves and then spreading to the older

leaves ; chlorotic areas become necrotic.

Boron.—Young bud leaves and petioles light

in color, and often deformed in shape ; terminal

buds dying and new lateral shoots appearing;

leaves tinted purple, brown, and yellow; some

fruit pitted with corky areas in the skin.

Molybdenum.—Mottling of older leaves

while veins remain light green; new leaves

green at first but becoming mottled as they expand; leaves curling inward and dying back

from the tips.

Zinc.—New leaves usually small and mottled

with yellow ; dead areas common.

Copper.—Leaves generally chlorotic and

lacking turgidity; growth of entire plant retarded.

Sulfur.—Lower leaves thick, firm, and yellow-green in color; stems woody, elongated,

and spindly.

CROPPING PLANS

Greenhouse tomato production is often combined with the production of lettuce, cucumbers, or flower crops in various sequences. The

markets available and the anticipated prices of

the different commodities determine the crops

to grow and the growing sequence.

Six possible crop sequences used by greenhouse tomato growers are given below :

Plan 1—Spring and fall tomato crop

Tomatoes.—Seed sown October 25 to November 10; plants set in houses about January 10;

vines removed July 1 to August 1.

Tomatoes.—Seed sown June 15 to July 1;

plants set in houses August 1 to 15; vines removed December 15 to January 1.

Plan 2-'Early'Spring tomato crop

Lettuce.—Seed sown August 15 to September 10; plants set in houses September 15 to

30; crop harvested October 15 to November 15.

Tomatoes.—Seed sown September 15 to 30 ;

plants set in houses November 15 to 30; vines

removed Juiy 1 to August 1.

Plan 3—Mid'to late-spring tomato crop

Lettuce.—Seed sown August 1 to 15; plants

set in houses September 1 to 15 ; crop harvested

November 15 to 30.

Lettuce.—Seed sown October 15 to 30;

plants set in houses November 15 to 30; crop

harvested February 1 to 28.

Tomatoes.—Seed sown January 1 to 15;

plants set in houses March 1 to 15; vines removed July 15 to August 1.

Plan 4—Fall tomato crop

Tomatoes.—Seed sown June 15 to July 1;

plants set in houses August 1 to 15 ; vines removed December 20 to 31.

Vegetable and Flower Plants.—January to

June.

Plan 5—Fall tomato crop

Tomatoes.—Seed sown July 1 to 15; plants

set in houses August 15 to 30; vines removed

December 15 to 31.

Lettuce.—Seed sown November 15 to 30;

plants set in houses December 15 to 31; crop

harvested March 15 to 31.

Cucumbers.—Seed sown February 1 to 15;

plants set in houses April 1 to 15; vines removed July 1 to 15.

Plan ó—Spring tomato crop

Tomatoes.—Seed sown December 15 to January 1; plants set in houses February 1 to 15;

vines removed July 1 to 15.

Flowers.—Chrysanthemums, poinsettias, or

other flower crop.

The predominant cropping plans in the large

greenhouse vegetable-producing areas of Ohio

and Indiana are Plans 1 and 2, in which either

2 tomato crops or a lettuce crop and a spring

tomato crop are grown each year. In the

Northeastern States, all of the above-mentioned cropping plans and variations of them

are likely to be found. In the Southwest it is

common to seed between August 1 and September 1 for Thanksgiving and Christmas harvests.
COMMERCIAL PRODUCTION OF GREENHOUSE TOMATOES 11

Some growers use two or more plans simultaneously. For example, a grower may use his

entire growing area for tomatoes in the spring,

and in the fall use part of his growing area for

tomatoes and the rest for lettuce.

Since tomato plants do not fully occupy the

space between rows during early stages of

growth, a quick-maturing crop such as lettuce

is sometimes planted between the rows. When

intercropping, conditions best suited for the

development of the tomatoes should be maintained, even though these conditions are not

ideal for the companion crop.

The prevailing environmental conditions

should be studied when considering cropping

schedules. For example, in practically all areas

of the United States, it is not economically feasible to produce greenhouse tomatoes for harvest during January and February. The days

during the preceding months are short and

sunlight is usually deficient, and these conditions result in poor fruit set, slow ripening,

and poor quality. Also, the cold temperatures

during these months may make fuel costs prohibitive.

Competition from field-grown tomatoes

should also be considered when determining a

cropping plan. The cost of producing greenhouse tomatoes makes it impractical to compete

with local field-grown fruit. Also, greenhouse

tomatoes for August and September harvest

are not likely to set fruit well and will be of

poor quality because of the high summer temperatures at which they are grown.

Generally, when a fall crop is grown, planting should be timed so that harvest starts soon

after the first killing frost or when local field

tomatoes are no longer available. A spring crop

should be timed so that harvest begins late in

winter or early in spring and terminates when

field-grown fruit become available.

Other factors to consider when selecting a

cropping plan are disease control and the maximum efficiency of the labor force. If two tomato crops are grown a year, it is difficult to

prevent a carryover of tobacco mosaic virus

from the fall to the spring crop unless the soil

is sterilized between crops, and this is expensive. Even when the main growing areas are

sterilized, there is a danger of transmitting the

virus from one crop to the next through the

young plants being started for the second crop.

Another possible disease problem is a severe

botrytis infection of tomatoes when lettuce is

intercropped. The disease-producing organism

may build up in the dense foliage of the lettuce

and move onto the adjacent tomatoes if proper

precautions are not taken.

To retain competent laborers on a yearround basis, it is necessary to distribute the

work load throughout the year as much as possible. If a single crop a year is to be grown, it

may be difficult to retain good help.

VARIETIES OF GREENHOUSE TOMATOES

Proper selection of a tomato variety assures

that the genetic potential is present for the desired yield, color, size, and quality of fruit.

Also, disease losses can often be averted by

growing resistant varieties.

When greenhouse tomatoes were first grown

in the United States, varieties from England

were used. These small-fruited, free-setting varieties included Carter's Sunrise, Sterling Castle, Comet, and Best of All. These and the varieties Potentate and Ailsa Craig, developed

later, were then used extensively as parents in

breeding new American greenhouse varieties.

As American consumers demanded larger

fruit, and new sources of disease resistance

and other desirable traits were discovered, several varietal development programs were established. From these programs such varieties as

Globe, Globe Strain A, Ohio Wilt-Resistant

Globe, Michigan State Forcing, Spartan Hybrid, Michigan-Ohio Hybrid, Waltham Forcing,

Improved Bay State, and Waltham Moldproof

Forcing were developed. Some of these varieties are still grown, but many newer releases

are now available.

In the United States, market preferences

greatly influence the choice of varieties grown

in different regions. In the Northeastern

United States, small, 3-to 4-ounce types are

most popular. In most other areas, fruits
12 AGRICULTURE HANDBOOK NO. 382, U.S. DEPT. OF AGRICULTURE

weighing 6 to 8 ounces are preferred. Preferences for color of the ripe fruit also differ.

Most northern Ohio growers produce pinkfruited tomatoes, while red-fruited varieties are

grown in southern Ohio.

Desirable characteristics that a greenhouse

tomato should possess include :

1. The ability to set fruit and yield well

under a range of environmental conditions.

2. Resistance to diseases such as fusarium

wilt, verticillium wilt, and leaf mold.

3. A low incidence of fruit cracking, blotchy

ripening, and blossom-end rot.

4. Fruit with good quality, including internal and external color, flavor, firmness, and

smoothness.

5. The ability to respond to fertilization and

watering without overresponding.

Most varieties grown have been developed

specifically for greenhouse production, although some varieties developed for field production are grown in greenhouses. Both openpollinated varieties and Fi hybrids are grown.

Since many varieties are available and new

ones are developed each year, it is difficult to

provide a complete listing. Some of the currently popular varieties are given in table 1,

along with some of their characteristics.

Growers may keep abreast of the latest developments in greenhouse varieties through

contact with their State experiment station

and vegetable seed companies.

Some varieties popular in the Northeastern

States are Tuckcross 0, Michigan-Ohio Hybrid, Waltham Disease-Resistant Hybrid, and

Veegan. In the Middle West, Michigan-Ohio

Hybrid, Michigan State Forcing, Ohio WR25,

Ohio WR29, and Ohio Hybrid 0 are the most

popular varieties. Southeastern growers use

Michigan-Ohio Hybrid; Michigan State Forcing; Tuckcross M, 0, and V; Manapal; and

Floradel. Growers in the Western and Southwestern States grow many of the same varieties grown elsewhere plus several additional.

These include Tuckcross 0 and V; MichiganOhio Hybrid; Floradel; Floralou; Manapal;

Pinkshipper; Spartan Red; and Spartan Pink.

Growers should be aware that all varieties

cannot be treated alike. Fertilization and irrigation practices and proper spacing to attain

maximum yields may vary with different varieties. Also, some varieties perform best as a

fall crop while others do best in the spring.

TABLE 1.—A partial list of tomato varieties for greenhouse production

Variety name Fruit color Disease resistance ^ Fruit size

Michigan State Forcing __.

Michigan-Ohio Hybrids

Ohio WR7

Manalucie

Manapal

Tuckcross, M, 0, and V

Spartan Red

Ohio WR29

Ohio WR25

Waltham Disease-Resistant

Hybrid

Ohio Hybrid 0

Veegan

Red Moderate-fusarium

Red Fusarium

Pink Fusarium, blotchy ripening, fruit pox

Red Fusarium, blossom-end rot, leaf mold

Red Fusarium, blossom-end rot, leaf mold

Red Fusarium, leaf mold

Red Fusarium

Pink Fusarium, blotchy ripening, fruit pox

Pink Fusarium, blotchy ripening, fruit pox

Medium to large.

Medium to large.

Medium to large.

Medium to large.

Medium to large.

Small to medium.

Medium to large.

Medium to large.

Medium to large.

Red Fusarium, leaf mold Small to medium.

Pink Fusarium, leaf mold Medium to large.

Red Fusarium, leaf mold Medium to large.

^ At least 10 races of leaf mold

tain races.

exist in this country. Varieties listed as resistant may be resistant to only cer-
COMMERCIAL PRODUCTION OF GREENHOUSE TOMATOES 13

STARTING THE PLANTING STOCK

Practically all greenhouse operators grow

their own tomato plants from seed. The grower

thus assures himself of having plants of the

desired variety and at the proper stage of development when he v/ishes to plant the crop.

Also, plants grown locally can be transplanted

into the permanent beds with the least shock.

Number of Seeds and Plants Needed

Only the best seed obtainable should be used.

The cost of seed is relatively small compared

with the large investment in equipment and

labor needed to grow a crop. The seed used

should be new. It should have been stored

under proper conditions to retain a high percentage of germination. The seed should be

free of seedborne diseases. If Fi hybrids are

used, new seed must be purchased for each

crop. It must not be saved from the preceding

crop because it will not breed true.

An ounce will contain 8,000 to 10,000 wellmatured tomato seeds. This number should be

sufficient to produce at least 5,000 strong

plants. However, it is good insurance to grow

more plants than will be needed to set the

available bed space. Growing additional plants

costs more for supplies and labor, but may be

the difference between a crop and no crop, if

something should happen to part of the seedlings.

The number of plants needed depends on the

amount of bed space to be allotted each plant

and the total bed space to be planted. The variety being grown, season of the year, soil fertility, and importance of fruit size influence the

plant spacing. Experience has shown that some

varieties yield more fruit at high plant populations than other varieties. Some growers plant

at a closer spacing for a fall crop to help attain

a satisfactory total yield, since less fruit will

be set per plant in the fall. Care must be taken

that close spacing does not reduce fruit size

below that demanded by the market. More fertilizer may be necessary when spacing is close.

Growers space plants from 12 to 24 inches

apart in the rows, with rows 3 to 4 feet apart.

A common spacing is 18 inches by 3 feet,

which allows 4 1/2 square feet per plant or

10,890 plants per acre. For other spacings the

number of plants needed can be estimated by

dividing the total number of square feet of bed

space to be planted by the number of square

feet provided for each plant. Number of plants

per acre required for various spacings is given

in table 2.

TABLE 2.—Number of plants required per acre

for various plant spacings

Plant spacing in Row spacing No. plants

row-inches in inches '^ per acre

12 36 14,520

12 42 12,445

12 48 10,890

15 36 11,616

15 42 9,945

15 48 8,712

18 36 9,680

18 42 8,297

18 48 7,260

21 36 8,297

21 42 7,118

21 48 6,223

24 36 7,260

24 42 6,223

24 48 5,445

^ For alternating row spacings, average the row

widths and use this average for determining the number of plants required.

Time for Sowing Seed

The date for sov^ing seed is governed by the

time desired for the first harvest. About 4 1/2

months from seeding to harvest should be allowed for a fall crop and 5 1/2 months for a

spring crop. Plants grov^n in summer and early

fall develop faster than those grown in late

fall and early winter months. The location of a

greenhouse also influences the time of seeding.

Demands for greenhouse tomatoes increase

immediately after the outside crop has been

killed by frost. This and the difficulty of obtaining a good set of fruit after the prevailing
14 AGRICULTURE HANDBOOK NO. 382, U.S. DEPT. OF AGRICULTURE

cloudy weather that starts in November, make

earlier fall plantings more profitable. Since it

takes 50 to 60 days to develop tomatoes from

blossom to full ripeness under late fall and

winter conditions, tomato plants that are to be

removed by mid-January must have all their

fruit set by mid-November.

Greenhouse growers vary the time of sowing

the seed for the early spring crop to fit the

crop into diverse cropping systems. If a long

tomato-growing season is desired, the seed

must be sown early. Experiments have shown

that earlier planting not only produces the

largest yields, but also usually brings better

prices on the early spring market. In most

areas, seed for the spring crop is sown as early

as October 25. The plants are set in permanent

ground beds about January 10, and the harvest

begins around the first of April.

It is important to use seeds free of diseaseproducing organisms. Treated seed should be

purchased, or the seed should be treated as described in the USDA Agriculture Handbook

203, 'Tomato Diseases and Their Control."

Growers who save their own seed should use

only ripe fruit and extract the seed with a hydrochloric acid treatment to eliminate tobacco

mosaic virus on the seed surface. One fluid

ounce of concentrated hydrochloric acid should

be added to the seed, pulp, and juice taken

from 5 pounds of fruit. The material is soaked

and stirred occasionally until the seed settles

to the bottom. The seed is then ready to be separated from the pulp by washing thoroughly

with water.

Seeding

Two basic systems are used for starting tomato seedlings: (1) Seeding directly in small

pots or growing containers; or (2) Seeding

into flats and later transplanting into growing

containers. The first method involves less handling of the small plants; therefore, less labor

is required and there is less chance for the

spread of tobacco mosaic virus. Also, the seedlings develop more rapidly because the roots

are not disturbed by transplanting. Growers

who seed in flats and transplant into pots may

do so because of space limitations or because

they feel they obtain superior-quality plants.

The medium used for starting seedlings

should permit good germination and subsequent root growth, be economical to use, be

chemically and physically uniform, and be free

of disease. Several materials can meet those

criteria, including loam or sandy soil, sand,

shredded sphagnum peat moss, vermiculite,

and perlite. These materials are usually mixed

together in various combinations for the best

results. Some combinations used for starting

tomato seedlings are :

1 part compost : 1 part sand : 2 parts topsoil.

1 part peat moss : 1 part vermiculite.

2 parts sand : 1 part peat moss.

1 part soil : 1 part peat moss : 1 part perlite

or sand.

1 part compost : 1 part vermiculite.

1 part perlite : 1 part peat moss ; 1 part vermiculite.

The medium used should be sterilized with

heat or chemicals before the seeds are planted

unless it is known to be free of disease-producing organisms. Also pots, flats, and any tools

used should be sterilized. Materials and methods for sterilizing are discussed in USDA Agriculture Handbook No. 203, "Tomato Diseases

and Their Control."

Direct seeding may be into 3- or 4-inch clay

or peat pots or some of the newer plant-growing containers (fig. 5). The pots are spaced out

and filled with the sterilized potting medium to

within about 1/2 inch from the top of the pot.

One to three seeds are planted 1/3 to 1/2 inch

deep in the center of each pot. Seeds should be

planted at a uniform depth so they will germinate evenly and result in uniform plants for

transplanting into the beds. After germination,

pots with more than one seedling should be

thinned to a single plant.

When seeding is done in flats, seeds are sown

in rows 1/2 inch deep and 2 to 3 inches apart

(fig. 6). A wooden lath notched on the ends so

it will make a row of the proper depth when

pressed into the soil may be used. Seed should
COMMERCIAL PRODUCTION OF GREENHOUSE TOMATOES 15

BN-36540

FIGURE 5.—Sowing tomato seeds in peat pots.

be distributed 7 to 8 per inch in the rows and

covered with the germinating medium.

BN-3e523

FIGURE 6.—Sowing tomato seeds in a flat, a method

commonly used for starting greenhouse tomatoes.

For good germination of tomato seed, the

soil must be kept moist. Temperatures of 70°

to 80° F. are recommended during the germination period. To help maintain proper temperature and moisture for germinating seeds, the

flats or pots may be covered with panes of

glass or sheets of plastic until the seedlings

break through the soil surface. After germination, the soil surface should be wet only as

often as necessary to keep the young plants

growing. It has been shown that night temperatures of 52° to 54° F. and day temperatures

of 56° to 58° F. during the 2 to 3 weeks following cotyledon expansion can result in the

ñrst cluster of fruit being formed earlier and

more flowers in the first and second cluster.

Following the cold treatment, temperature

should be maintained between 60° to 70° F to

promote stocky growth of the seedlings.
16 AGRICULTURE HANDBOOK NO. 382, U.S. DEPT. OF AGRICULTURE

GROWING THE TRANSPLANTS

The productivity of a tomato crop is to a

large extent determined by the quality of the

transplants set in the beds. A grower can control the quality of his transplants by controlling temperature, water, nitrogen, carbon dioxide, and light. It is very important that these

factors be kept in the proper balance.

Transplanting of young seedlings from seed

flats should be done as soon as their stems have

straightened and the seed leaves (cotyledons)

have opened horizontally. This is usually 9 to

14 days after the seed is sown (fig. 7). The

sooner the seedlings are transplanted, the more

quickly they recover from the shock. When

transplanting young tomato seedlings, the

grower should always grasp the plant by one

of the seed leaves. Slight pressure on the stems

can easily injure the seedlings permanently.

Seed planted directly in clay or peat pots or

some other growing container do not require

transplanting.

It should be a routine practice for all persons to wash their hands in strong soap and

water before handling young tomato plants to

avoid infecting them with mosaic viruses.

Workers should not be allowed to use tobacco

in any form while working around the plants.

After smoking or handling tobacco, workers

should always wash their hands again before

starting back to work. Also, only clean clothing, including shoes, should be worn by

workers.

Plants obviously infected with a mosaic

virus should be pulled and destroyed immediately. The workers' hands and any equipment

that come in contact with the plants should

then be washed thoroughly.

Since the plants for the spring crop must be

grown during the shortest and cloudiest days

of the year, it is important to provide the best

possible conditions for their proper development. The soil in which the plants are grown

should be well-aerated and high in phosphate

and potash, but low in nitrate nitrogen.

High nitrate content of the soil with abundant moisture during short days will cause

plants to grow soft and spindling. Under these

conditions the first flower buds often fail to

develop properly and produce no viable pollen.

The buds frequently drop off and delay fruit

setting for weeks. Plants grown slowly in soil

low in available nitrogen with moderate soil

moisture will grow into a fruitful condition

during the winter. With some of the smallfruited varieties, it is not so important to keep

the available nitrogen in the soil at such a low

BN-36B41

FIGURE 7.—A flat of tomato seedlings at the proper stage for transplanting.
COMMERCIAL PRODUCTION OF GREENHOUSE TOMATOES 17

level. These varieties set fruit quite readily

even when the days are short and there is considerable cloudy weather. Where more nitrogen

can be made available during this period, the

plants develop and mature more quickly.

When plants are grown in summer for early

fall planting, the days are long and usually

bright. These conditions encourage high production of carbohydrates (sugar, starch, and

cellulose), and hence plants need larger

amounts of nitrogen during summer. The

plants tend to become nitrogen-starved, so

more nitrates must be supplied to maintain

good growth.

To obtain normal growth and fruiting of tomato plants a balance between the amount of

nitrogen available to the tomato plants and the

rate of carbohydrates manufactured in these

plants must be maintained. The successful tomato grower learns to recognize this growth

relationship and to know what to do to keep

the carbohydrate-nitrogen ratio in proper proportion.

While the transplants are growing, the

night temperature should be kept as close to

60° F. as is practical, with day temperatures

maintained between 60° and 70°. The transplants should be watered only as often as is required to keep them growing continually. Watering should be done early in the morning so

the foliage will dry rapidly and prevent disease

epidemics. If the transplants cannot be set in

the ground bed on schedule, water can be withheld to slow down growth.

Eight to ten weeks after seed germination

the plants should be 8 to 10 inches tall, with

strong roots, and with the first fruit buds partly developed (fig. 8). They may be somewhat deficient in nitrogen, as indicated by a

light yellow-green color of leaves and by a purple tinge of stems and petioles. Plants at this

stage should be firm but riot hard and woody.

The plants should be set in the ground beds at

this time. If they are held much longer, the

root systems will become potbound and plant

growth will be stunted. Good transplants ready

to be set in the beds should be as wide as they

are tall.

If the plants should become too hardened

before transplanting, an ounce of sodium or

FIGURE 8.-

BN-86536

-A good tomato plant ready to be set in a

greenhouse bed.

ammonium nitrate per gallon of water will

stimulate renewed growth. Complete water-soluble starter fertilizers are also available that

furnish the plants better balanced nutrition. A

good starter solution may be made by dissolving 3 pounds of 10-52-17 fertilizer in 50 gallons of water. A half pint of this solution per

plant is usually ample to stimulate renewed

growth. It is best to pour the fertilizer solution

directly into each pot a day or two before

plants are to be transplanted out in the greenhouse beds. The starter fertilizer will give the

plants a quicker start, thus hastening the first

harvest.

Research has shown that young tomato

plants respond more to carbon dioxide enrichment than older plants do. Therefore, enrichment of the atmosphere with carbon dioxide

during the growth of the transplants is an effective means of accelerating their growth rate

and increasing the eventual yield of fruit. A

more thorough discussion is given in the section on Carbon dioxide enrichment.

Although most growers in the United States

do not presently supply artificial light to transplants during their growth, tests show that

supplemental artificial light during normal daylight hours can increase the eventual fruit
18 AGRICULTURE HANDBOOK NO. 382, U.S. DEPT. OF AGRICULTURE

yields significantly. High-intensity lamps supplying at least 500 ft.-c. at the leaf surface

should be used. Artificial light in combination

with carbon dioxide enrichment offers a promising prospect for increasing the quality of

tomato transplants.

PREPARING FOR PLANTING

The first step in preparing the greenhouse

bed for a new crop is to dispose of all debris of

the preceding crop. Before the old vines are removed, all insects on them should be destroyed

to prevent their reentry into the greenhouse.

Old vines should then be moved several

hundred yards from the greenhouse and destroyed. When plants are piled near the greenhouse, spores of disease-producing fungi may

blow back into the house.

After the bed is cleaned, the first consideration should be sterilization of the soil to kill all

potential tomato pests in it. Sterilization, if

done effectively, will destroy weed seeds, insects, nematodes, and disease-producing fungi,

bacteria, and viruses.

Many growers sterilize twice a year or before every crop. Other growers prefer to sterilize only once a year. The cost of sterihzation,

the possible benefits to be derived, and the

cropping plan being used must be considered

when deciding whether to sterilize once or

twice a year.

The two general methods for sterilizing

greenhouse beds are through the use of heat or

chemicals. In large permanent estabhshments,

steam is generally used for sterilization because these houses are heated with steam.

Houses not equipped for steam heating must be

sterilized with chemicals.

For steam sterilization, steam is diverted

from the boiler and forced through a permanent system of 3- or 4-inch tile buried about 15

inches deep in rows 18 to 24 inches apart. The

lines are all connected at one end by elbows

and tees. At the other end a header made of

21/2- or 3-inch pipe delivers the steam to the tile

lines.

The tile should be laid so that about 14 inch

is left between them at joints. This allows

room for the tile to swell when wet and for

steam to escape into the soil. It is best if the

tiles are laid with a slight grade away from

the header to prevent water from collecting at

the header.

The time required to sterilize plant beds varies with the size of the steam line, the steam

pressure, and the soil type. It is generally recommended that the soil be heated to 180° F.

and held at this temperature for 4 hours. Thus

if 4 hours are required to heat the soil to 180°,

the total sterilization time will be 8 hours.

To retain the heat in the soil during sterilization and insure uniform heating throughout, it is necessary to cover the soil during the

heating process. Polyethylene film, black building paper, synthetic rubber sheets, or specially

made cloth covers may be used.

Before sterilization, the soil should be cultivated and well pulverized. Best results are obtained when the soil moisture is such to allow

for good cultivation.

Pathogenic fungi, bacteria, nematodes, and

weed seeds in soil can be controlled by chemicals. Some available chemicals control all kinds

of organisms; others control only one or various combinations. For a thorough discussion on

soil sterilization with chemicals, see USDA

Agriculture Handbook No. 203, 'Tomato Diseases and Their Control."

After sterilization, extreme care must be

taken to prevent recontamination of the soil.

Since no competing organisms remain in the

soil after sterilization, the growth of a pathogen reintroduced into the soil goes unchecked.

To help prevent recontamination, all hand and

power tools should be sterilized before being

used. Also, walkways in the greenhouse should

be sterilized, and workers should not be allowed to move from unsterilized to sterilized

areas without having clean clothing and clean

shoes.

After the soil has been sterilized and allowed to lie idle for 2 weeks or more, any lime

or fertilizer to be applied should be broadcast

onto the soil surface. Amount and types of materials used are discussed in the section on
COMMERCIAL PRODUCTION OF GREENHOUSE TOMATOES 19

Plant nutrition and fertilization. The fertilizer, lime, and any mulch from the preceding

crop is then worked into the soil as it is prepared for planting.

Many types of equipment are available for

preparing the soil. Rotary soil pulverizers are

widely used and do an excellent job of preparing a deep, fluffy soil bed in one operation.

Many large growers use tractor-driven rotovators (fig. 9), but small growers may, use

smaller, self-propelled cultivating equipment.

In soils that contain little organic matter,

particles tend to cement together again after

the plants have been set and the soil has been

watered several times. This deprives the roots

of oxygen and moisture, as well as making root

penetration more difficult. As a result many

roots die, the plants grow more slowly and

yield less fruit.

An unfavorable physical condition of the

soil can be improved by incorporating an abundance of organic material into it. Organic materials are often applied in summer just before

planting the fall tomato crop, rather than in

the winter preceding the spring crop. Heavy

soils require more organic matter than light

BN-36B29

FIGURE 9.—Tractor and rotovator for preparing soil

beds in a large greenhouse.

soils to keep them loose and friable. Sources of

organic matter will be discussed in the section

on Mulching.

After cultivation, the beds are usually

marked to indicate precisely where the plants

will be planted. In large houses, furrows about

6 inches deep are often made with a small tractor.

PLANTING

Houses should be warmed thoroughly before

the plants are set during winter weather. To

encourage prompt growth of plants, some

growers introduce steam into the tile used for

steaming the soil, until the soil temperature is

raised to 70° F. Warmed water is also used

sometimes at transplanting time to help the

plants start growing more quickly. If soft vegetative plants have to be used for winter

planting, starter fertilizers and extra heat

should be omitted.

The sequence of planting operations varies

according to the grower's plans. Many growers

set the plants in place but leave them in the

pots a week or two longer so they reach the

right bud stage before setting in the ground

bed.

It is very important, except when growing

free-setting varieties, to have the first bud

cluster at the proper stage of development before planting so the blossoms will open normally and set fruit. The grower must not allow

the plants to take root in the soil beneath them

if a mulch has been spread and they are sitting

on the mulch. If the roots are allowed to penetrate into the bed soil, the nitrogen and moisture available many cause the plants to become

succulent and vegetative, leading to failure to

develop normal blossoms.

Most growers water the potted plants thoroughly the day before they are to be planted in

the permanent beds. If the plants are in clay

pots, they are then easily removed without disturbing the root by inverting the plant and

jarring it out of the pot.

The plants are set in holes or trenches, 1 to 2

inches deeper than they were in the growing

container. If peat pots are used, it is important

that the pot be set deeply enough that the top

is covered with soil and does not act as a wick
20 AGRICULTURE HANDBOOK NO. 382, U.S. DEPT. OF AGRICULTURE

to dry out the plant roots. After the plants

have been set, the mulching material should be

leveled around them, if it has already been

spread. The plants should also be watered

enough to settle the soil around the roots and

to provide sufficient moisture for good grov^th.

A common practice is to apply a soluble

starter fertilizer v^ith the first watering or

two. Three pounds of 10-52-17 per 50 gallons

of water is adequate. One-half to one quart

should be applied around each plant.

Tomato plants should be handled as little as

possible to avoid the spreading of virus diseases through the plants. When they must be

handled, the operator's handS; clothing, and

tools should be washed free of any possible

virus contamination before touching any tomato plants. Also, smoking should not be allowed in the greenhouse.

MULCHING

A common practice in greenhouse tomato

production is to use an organic mulch. Mulches

serve the following purposes: (1) To help

maintain more uniform soil moisture, thereby

lessening fruit cracking; (2) to add organic

matter to the soil; (3) to reduce soil compaction and thereby improve soil aeration and root

growth; (4) to protect the fruit of the first

cluster from touching the soil and becoming infected with soil rots; (5) to reduce the amount

of spattering of water drops from the soil onto

the lower leaves, thereby reducing the spread

of diseases; and (6) to liberate carbon dioxide

during their decomposition.

A number of materials are satisfactory for

mulching greenhouse tomatoes. Some of the

most commonly used mulching materials are

wheat straw, peanut hulls, ground corncobs,

and manure. Other materials used include alfalfa, red clover, wheat and rye straw, various

types of hay, sawdust, wood chips, pine needles,

sphagnum peat, rice hulls, and sugarcane

bagasse.

The choice of mulch depends on the cost and

availability of the material, its ability to prevent soil compaction, its decomposition rate, its

effect on the nutritional balance of the soil, its

freedom from potentially harmful chemicals

such as herbicides, and the possibility that it

may carry a disease-producing organism into

the greenhouse.

The mulch may be applied after the soil has

been sterilized and cultivated just before planting, or it may be applied after the transplants

have been set in the ground beds. The mulch

should be spread over the entire soil surface to

a depth of 2 to 3 inches. Approximate amounts

required per acre are 6 to 8 tons of wheat

straw or similar materials, 12 to 14 tons

peanut hulls, and 10 to 12 tons ground corncobs.

TEMPERATURE AND HUMIDITY CONTROL

One of the most effective means of controlling plant growth is through regulating the

greenhouse temperature. Respiration, or the

process through which living plants constantly

use food, varies considerably with temperature. Likewise, photosynthesis, or the process

of manufacturing food during the daylight

hours, is controlled by temperature.

The rate of photosynthesis is determined

also by the amount of light available, so temperature must be coordinated with light conditions. On bright days when light does not limit

photosynthesis, the greenhouse temperature

may be higher than on dull days. When light is

limiting, a high temperature may increase the

respiration rate until the amount of food consumed by the plant is equal to or greater than

that produced by photosynthesis. Night temperature must be low enough to insure that the

food manufactured during the day is not entirely used up.

As stated in the section on Seeding, the temperature for tomato seed germination should

be 70° to 80° F. After germination a temper-
COMMERCIAL PRODUCTION OF GREENHOUSE TOMATOES 21

ature range of 60° to 70° F. is best for growing the planting stock, except for a cold treatment of seedlings.

After plants are in the beds and growing,

the night temperature should be held between

60° and 65° F. Day temperatures of from 70°

to 75° F. should be maintained on bright days.

The temperature may range as high as 80° on

clear days without adversely affecting the development of the crop. On cloudy days the temperature should be kept 65° to 68° F. When

this temperature schedule is maintained, fruit

buds should develop normally, and the fruits

should be smooth and of high quality. In no

case should the night temperature drop below

58° during fruit bud development, as this may

cause poorly formed blossoms that will abort,

or misshapen tomatoes of poor quality.

If carbon dioxide enrichment is used, research has shown that slightly higher temperatures should be maintained. On sunny days the

temperature may range up to 85° F. and on

cloudy days up to 75° or 80° F.

Greenhouse temperature is regulated by controlling the source of the heat, the ventilators,

or an evaporative cooling system. Environmental conditions influence the frequency with

which adjustments must be made. However,

temperature should usually be checked at

hourly intervals. On clear, sunny days the direct rays of the sun raise the temperature inside greenhouses very rapidly. During daylight

hours when the temperature of the greenhouse

reaches 70° to 72° F. all heat should be shut

off and the ventilators opened to prevent the

temperature from going higher.

Automatic thermostat-controlled steam

valves or heaters and ventilators make temperature control much easier (fig. 10). An alarm

system that warns of temperature extremes is

also very useful.

Shading with an external application of

whitewash or similar compound is used on

glass greenhouses to control temperature. The

white coating reflects the sun's rays and reduces their penetration into the greenhouse.

The time of application and removal of the

shading compound varies with the amount of

sunshine received and the conditions of a given

season. Generally, glass greenhouses should be

BN-36530

FIGURE 10.—Equipment for automatically controlling

greenhouse ventilators.

shaded about the time of transplanting to the

groundbed when a fall crop is grown. As the

days become shorter and the sun's rays more

indirect, the shading should be removed around

the middle of October. For a spring crop, an

application of shading is usually required about

the middle of April.

Ventilation is important, not only for maintaining temperature control but also to remove

stale, moisture-laden air and replace it with

fresh air. The introduction of fresh air and

consequently carbon dioxide is particularly important if carbon dioxide enrichment is not

used. The relative humidity inside the greenhouses should always be kept below 90

percent to keep under control the leaf mold

disease that is so destructive to greenhouse

tomato plants. If the humidity of a house is

allowed to go over 90 percent for 1 day, leaf

mold infections may result.

No rigid rules can be laid down for ventilating. Usually the ventilators are closed at night

during cold weather when heat must be kept

on in the houses. Even then, it may be necessary to "crack" (slightly raise) the top ventilators to maintain enough exchange of air to

prevent the humidity from building up. In

plastic greenhouses where exhaust fans are

used to ventilate, it may be necessary to run

the heaters and fans simultaneously to allow
22 AGRICULTURE HANDBOOK NO. 382, U.S. DEPT. OF AGRICULTURE

ventilation and at the same time to prevent the

temperature from dropping too low.

Heating and ventilation should be regulated,

if possible, so the atmosphere of the house is

kept in circulation. Outside air may enter the

greenhouse through opened side ventilators

and be warmed as it moves through the greenhouse, picking up excess moisture and carrying

it out through the top ventilators. This is especially helpful in controlling leaf mold. The

most dangerous times are during relatively

mild weather in fall and spring when proper

night temperatures may be maintained without

any heat in the greenhouse by keeping the ventilators closed. This is likely to create a combination of conditions inside the houses that will

start an epidemic of leaf mold raging through

the plants. A grower should never be tempted

at such times to save the small amount of fuel

needed to provide a little heat and sufficient

ventilation in the houses.

TRAINING AND PRUNING

Greenhouse tomato plants are usually supported by stout wires (Number 9-11) running

parallel to the soil surface, 6 to 8 "feet above it.

The wires are directly over the plants and are

attached to the greenhouse frame. Individual

tomato plants are then supported by sisal,

hemp, or synthetic twine tied to the overhead

wire with the other end tied loosely around the

stem of the plant near the ground (fig. 11). As

the plant grows, it is wound loosely around the

string, always in the same direction. The string

should be kept under the point of leaf attachment to the main stem. In this way, the leaves

will not be broken and the plant will be supported at the base of the leaf petioles so it will

not slip down the string. Do not attempt to

wrap higher than 6 inches below the tip of the

plant, as the stem is likely to snap off if wound

around the string all the way to the top. Fruit

clusters should be trained under leaves so they

are protected from sunscald.

With crops that will be harvested over a

long period of time, it is a common practice to

lower the vines after the first clusters are harvested. This makes it easier to prune, pollinate,

and harvest the top of the plant. Fruit on the

first cluster generally ripens when the sixth or

seventh cluster is setting fruit. So that the

vines can be lowered later, the pieces of supporting twine are cut 3 to 4 feet longer than

would otherwise be necessary. The vines are

lowered at the desired time by loosening the

twine and retying it nearer its end.

Occasionally late in the growing season

growers train the vines along the overhead

supporting wires or across the rows, but this is

generally not recommended because it cuts

down on the sunlight reaching the leaves. Others train the plants over the wires so the

weight of the plant and the fruit bend the

plant toward the ground.

: <?'>< '*^^3^í^¿í

BN-36539

FIGURE 11.—Tomato plant growing in a straw-mulched

bed, tied with twine and pruned to a single stem.
COMMERCIAL PRODUCTION OF GREENHOUSE TOMATOES 23

Light wooden or metal stakes are sometimes

used to support tomato plants (fig. 12). They

are pushed into the soil near the plant and, if

overhead wires are present, the stakes may be

tied to them. To support the plant to the stake,

soft twine can be tied tightly around the stake

2 to 3 inches above a leaf petiole, then looped

under the base of the petiole and tied with a

square knot. Plant ties, made of tape with wire

reinforcing, may also be used to support plants

to stakes.

The single-stem system of pruning and

training is almost universally used by greenhouse growers, although a few train plants to

two or three stems. Pruning is accomplished by

removing the small lateral shoots that appear

at the point where the leaf stem joins the main

stem (fig. 13). Fruit buds appear on the opposite side of the main stem, usually above or

below the points where the leaves are attached.

Pruning should be done at least once a week,

because the lateral shoots can be easily removed when they are still small without making large wounds. The shoots may be broken

off by hand or cut with small clippers. Pruning

by hand is usually preferred because it results

in less spread of plant viruses. When pruning

by hand, grasp the shoot to be removed with

the thumb and forefinger and bend it sharply to

one side, then snap it off with a sharp bend and

pull in the opposite direction. The reversal of

direction becomes increasingly important when

the shoot is large, to avoid injuring the leaf

axil or the main stem. Since the hand touches

only the shoot being removed, there should be

no spread of virus diseases from plant to plant.

Even when a serious effort is made to avoid

touching virus-infected plants, workers' hands

and clothing are bound to contact the virus if

it is present in the greenhouse. Therefore, it is

advisable that workers wash their hands with

soap and water after working with each row

or use disposable plastic gloves when handling

the plants. Clean clothing should also be proBN-36B42

FIGURE 12.—Tomato plants growing in a small plastic greenhouse and supported by wooden stakes.
24 AGRICULTURE HANDBOOK NO. 382, U.S. DEPT. OF AGRICULTURE

BN-36B37

FIGURE 13.—Pruning a lateral shoot from a greenhouse

tomato plant,

vided for the greenhouse workers at least

twice a week. The clothing should be washed

in detergent and hot water. If clippers or

knives are used to prune, these tools should be

periodically dipped in a 3-percent solution of

trisodium phosphate. Trisodium phosphate is a

household cleaner that can be purchased at

most hardware or paint stores.

After plants have reached the maximum

height desired, the terminal growing point

should be removed. The time for this is determined by the height of the greenhouse or by

the number of fruit that can be matured before

it becomes necessary to remove the plants to

start a new crop. Generally plants are topped

about 45 days before harvesting is expected to

stop. Normally a fall crop will be topped after

6 to 7 clusters of fruit have set per plant. A

spring crop will not be topped until about 13

clusters have been set. Topping plants diverts

all the food manufactured to the development

of fruit already growing on the plants. To

allow proper development of the last cluster of

fruit set, two leaves should be kept above the

top flower cluster.

As the lower clusters of fruit approach maturity, it may be desirable to prune off part of

the lower leaves if they are yellowing. This allows for easier harvesting of the lower fruit

clusters and helps to control leaf mold by permitting better air circulation. It may also make

watering easier, especially when automatic

equipment on the soil surface is used. Unnecessary pruning of leaves should be avoided because all organic food for fruit development

must come from the leaves. To yield well, the

plants need a maximum of functioning leaf

surface.

As plants are pruned during the season,

watch for deformed or rough fruit. Such fruit

will be salable only as culls, so they should be

removed as soon as they are detected. All food

produced by the plant can then be used to mature the remaining fruit on the plant.

WATERING

Adequate soil moisture is essential for obtaining good yields of high-quality tomatoes.

Overwatering can result in excess vegetative

growth at the expense of fruitfulness. By carefully controlling soil moisture, a grower can

maintain control of his plants. For example,

withholding water can slow excessive vegetative growth when high temperature and low

light conditions favor it. To maintain control

of plants growing in soil beds, they should not

be allowed to root deep enough to reach permanent water.

The cultural technique employed and the soil

type greatly affect the frequency of watering.

The soil in a ground bed can hold large

amounts of water, thus plants in soil beds usually do not require frequent watering. Tomatoes grown in trough culture, ring culture, or

hydroponics are in a limited amount of growing medium and require more frequent watering. The water-holding capacity of soil depends

greatly on the soil type. Heavy clay soils hold

much more water than light sandy soils.

During periods of intense sunlight, plants use

more water in carbohydrate manufacture, they

lose more water from their leaves by transpira-
COMMERCIAL PRODUCTION OF GREENHOUSE TOMATOES 25

tion, and evaporation from the soil surface is

higher. High relative humidity reduces the

amount of moisture lost from plants and soil.

The primary factor determining watering

frequency is the stage of maturity of the

plants. A crop may be ruined by too much

water when the plants are first set out. Later

in the season when the plants have matured

and are laden with growing fruit, much more

water is required by each plant, so overwatering is quite unlikely. For a spring crop, too

much soil moisture in January and February,

or during cloudy periods, tends to promote vegetative growth and reduce fruitfulness. Some

growers water with a hose for 4 to 6 weeks

after setting the plants or until after the first

clusters of fruit have begun to enlarge, taking

care to wet the soil just down to the root zone.

Until the second or third fruit clusters have

set, some growers prefer to water the spring

crop only when plants show signs of wilting.

Sometimes a spring crop will grow for 6 weeks

or longer with only spot watering before a general watering becomes necessary.

As the season advances, the lengthening

days and more intense sunlight promote more

normal flowers with abundant pollen and

faster fruit development. By mid-season,

ground beds are watered about once or twice a

week. From 1 to IV2 acre-inches equivalent of

water is usually applied each time to satisfy

the needs of the crop.

A fall crop should be watered frequently in

August and September when the plants are

young. Watering is reduced greatly in October

and usually discontinued completely by the

middle of November. It is important that the

vegetative growth of a fall crop be terminated

at the proper time to enable the limited carbohydrates being produced to go into the development and ripening of the fruit that are already set.

Generally, best growth and yield of tomatoes

are obtained when soil moisture is maintained

fairly uniform. This requires frequent watering and much labor, unless an automatic system is used.

Watering from overhead should be early in

the day and on sunny days so the foliage will

dry as rapidly as possible. Diseases are likely

to get started if tomato plants remain wet for

long periods.

Growers can use a soil auger or spade to

check the moisture content of the soil. They

should learn to recognize the moisture content

of their particular soil by its appearance and

by squeezing it in the hand.

CARBON DIOXIDE ENRICHMENT

One of the requirements for the growth of

green plants is the presence of carbon dioxide

(COo). This gas is necessary for photosynthesis, one of the fundamental processes in

higher plants. Photosynthesis is the process of

combining CO2 and water in plant leaves in

the presence of sunlight to form carbohydrates. These carbohydrates are the source of

energy used by plants in growing.

Light, temperature, and CO2 may all limit

the rate of photosynthesis and carbohydrate

production in plants. Research has shown that

adding CO2 to the atmosphere of a closed

greenhouse can increase tomato yields by increasing both fruit size and number of fruit

when the other factors are not limiting. The

addition of CO2 can also result in earlier-maturing tomatoes.

Carbon dioxide is normally present in the atmosphere at a concentration of approximately

0.03 percent, or 300 parts CO2 per million

parts air. Concentrations of 1000 to 1500 parts

CO2 per million parts of air in tomato-producing greenhouses usually give the best results.

CO2 dissipates rapidly if ventilators are

opened or if the greenhouse is not tightly constructed. For fall crops, the early stages of

plant growth come during the warm months of

summer and fall when ventilation of the greenhouse is necessary. A spring crop, however,

makes its early growth during January and

February, when proper temperature and humidity can be maintained without ventilation.

As a result, yield increases are usually greater

for spring crops than for fall crops. Care must

be taken not to permit temperatures to rise

above 80° F., or fruit set and fruit size may be

adversely affected. Also, soil moisture and
26 AGRICULTURE HANDBOOK NO. 382, U.S. DEPT. OF AGRICULTURE

plant nutrition must be controlled precisely

when CO2 is used, since plants become more

vigorous and the tissue more succulent.

Research has shown that young plants are

particularly sensitive to CO2 enrichment. In

proper balance with the other factors influencing growth, extra CO2 can stimulate growth

of newly germinated seedlings and shorten the

time required to grow the transplants.

Liquid CO2 and combustion of organic fuels

are the sources of CO2 used in greenhouses.

The latter is most often used, because it is

cheaper to manufacture CO2, even though the

equipment for combustion is more expensive

initially than the equipment for using the liquid form. When CO2 is manufactured by combustion, care must be taken to prevent the

possibility of injury to the crop from toxic

substances such as carbon monoxide, sulfur

dioxide, and others. The proper selection of

burner and fuel can prevent such losses.

Some CO2 generators introduce the gas directly into the greenhouse, and other larger

units located outdoors or in a headhouse distribute the gas through a series of plastic or

metal ducts (figs. 14, 15, 16). After CO, is introduced into the greenhouse, it will rapidly

diffuse throughout.

FIGURE 15.—Plastic tube for distributing

dioxide.

BN-36626

carbon

BN-36B27

FIGURE 14.—Carbon dioxide generator for a large

greenhouse.

BN-36B32

FIGURE 16.—Carbon dioxide generator for small

greenhouse.
COMMERCIAL PRODUCTION OF GREENHOUSE TOMATOES 27

POLLINATION

Pollination is the transfer of pollen from the

stamens or male flower organs to the stigma or

female organ (fig. 17). Pollen is shed from the

inner side of the stamens of fully opened tomato flowers. Those pollen grains reaching the

sticky, moist stigmatic surface adhere. If conditions are favorable, the pollen grain germinates and sends a tube down the style and into

the ovary, where it unites with a ovule. The

contents of the pollen tube and ovule then fuse,

and fertilization is accomplished.

Tomatoes growing outdoors are pollinated

naturally by air movement that shakes the

flowers enough to dislodge the pollen and distribute it evenly over the stigmatic surface.

Because there is little air movement in a greenhouse, tomatoes grown indoors usually require

artificial pollination to set a good yield of fruit.

The general shape, size, and smoothness of the

fruit is largely determined by the thoroughness of the pollination. Since a single pollen

grain is required to fertilize each seed in the

tomato, many are required to fertilize each

fruit. When all the seeds are fertilized, the tomato will enlarge uniformly; but incomplete

fertilization will result in misshapen fruit.

This is a common cause of low-grade fruit.

The time necessary for a ripe tomato to develop from a fertilized flower varies with the

season. In winter it usually takes about 60

days; in early spring about 55 days; starting

in June, 40 to 45 days.

Artificial pollination of greenhouse tomatoes

is generally done mechanically. Chemical treatments may be used as a supplement when mechanical pollination alone will not result in

satisfactory fruit set.

Mechanical Methods

Pollination should begin as soon as the first

flowers are fully opened and continue as long

as there are flowers or until the number of fruit

have set that the grower desires. Ideally, pollination should be done every sunny day, but if

this is not possible, it should be done at least

every other day. Cool, cloudy weather can

prevent pollen from being shed, so pollination

may not be as effective on these days. Pollen is

more likely to be shed if pollination is performed between 9:00 a.m. and 3 :00 p.m. Shedding pollen can be easily seen falling from the

flower.

An efficient method of pollinating is to use

an electric vibrator that operates from an ordinary electrical outlet or a dry-cell battery (fig.

18). The electrical current rapidly vibrates a

wire loop or straight piece of wire. The wire is

placed in contact with each flower cluster that

has fully opened flowers. Since tomato flowers

usually hang downward, the vibration shakes

the pollen loose and it falls onto the stigma.

The vibrator may be moved from one flower

cluster to another as rapidly as possible.

Tomato fruits usually set without much difficulty on the first blossom clusters of the fall

crop and the later blossom clusters of the

spring crop because of the more nearly ideal

environmental conditions. Under these circumstances, simpler methods of assisting flower

fertilization may be satisfactory. One method

commonly used is to walk between plant rows,

tapping each overhead wire sharply with a

stick. The vibrations travel along each wire

in both directions so the flowers of plants in

adjoining rows are also jarred. Thus, the blossoms of all plants are repeatedly shaken as the

operator taps each wire again when he walks

between the next two rows of plants. Some

growers prefer to jar each plant directly by

STIGMA

STAMENS

COROLLA

CALYX

FIGURE 17.—Parts of a tomato flower.
28 AGRICULTURE HANDBOOK NO. 382, U.S. DEPT. OF AGRICULTURE

tapping it with a rubber-covered stick. This

method is effective, but there is the danger of

bruising the plants or the growing fruits.

Air blowers have also been used for pollinating greenhouse tomatoes. A blower is moved

between rows and a stream of air is directed at

the flower clusters. Care must be taken to

avoid damaging flowers by holding the nozzle

of the blower too close when the air is moving

at a high rate of speed.

Light, temperature, and humidity affect pollination. Cool, cloudy weather may prevent the

production of pollen. Even if pollen is shed on

cloudy days, it has been shown that pollen germinates best in sunlight. Optimum temperatures discussed in the section on temperature

and humidity control will allow good pollination.

High humidity is usually associated with

dull, cloudy days. Excessive humidity may

prevent dehiscence of pollen from the anthers

even though ample pollen is produced. Also,

very low humidity may result in poor fertilization by causing the pollen to dry out and therefore be less vigorous.

The humidity in a greenhouse can be lowered by increasing the heat for about 2 hours

before pollinating and maintaining it until pollination is completed. In areas of the country

where high temperature and low humidity is a

problem, a pad-and-fan cooling system is helpful.

Chemical Treatments

Hormonelike chemicals are available to supplement pollination. These materials should be

used only when greenhouse conditions are too

adverse for pollination alone to be effective in

setting fruit.

The fruits of some varieties set by chemical

treatments grow soft and do not keep well.

Buyers can sometimes distinguish treated

fruits from untreated by the remains of the

blossom caught under the sepals of the treated

fruits, and they are likely to discriminate

against them. The firm, smaller fruited varieties, grown in the northeast and north-central

regions, seem to be less subject to softening by

treatment with hormonelike chemicals, and the

treated fruits are marketed satisfactorily.

BN-86625

FIGURE 18.—Pollinating tomato flowers with an electric

vibrator.

When chemical treatment is used, the flower

clusters should be sprayed with the hormone

only after several flowers have opened. Treating immature flowers results in a poor set of

relatively small-sized fruit. In the bud stage of

a flower, both the pollen and the ovules are adversely affected. A hormone spray should be directed so as to avoid as much as possible spraying the immature terminal vegetative parts of

the plant, which tend to develop abnormally

when thus treated. Hormone treatments are

most satisfactory when applied to the face of

the flower.

All chemicals used for stimulating fruit setting must be approved by the United States

Department of Agriculture and The Food and

Drug Administration before their commercial

use with greenhouse tomatoes if the fruit is to

be shipped in interstate commerce. Do not use

chemicals on the basis that it may have been

legal to use them prior to January 1, 1970. The

grower may determine if the material he plans

to use has been cleared by contacting his State

Agricultural Experiment Station.
COMMERCIAL PRODUCTION OF GREENHOUSE TOMATOES 29

DISEASES

Disease control is essential to profitable

greenhouse tomato production, but it requires

constant watchfulness. Because of the close

spacing and frequent handling of plants, the

opportunities for spread of disease-producing

fungi, bacteria, and viruses are somewhat

greater than with tomatoes in the field. Also,

the closed environment is often conducive to

the rapid development and spread of diseases.

On the other hand, soil sterilization and control of temperature and humidity afi'ord means

of disease prevention and control that are not

possible when plants are grown outdoors.

Diseases such as fusarium wilt, verticillium

wilt, leaf mold, mosaic, and root knot occur

frequently in greenhouses. Regular practices of

sanitation are needed to prevent serious losses

unless resistant varieties are grown. Sanitation

also reduces losses from diseases such as stem

rot, botrytis rot, streak, spotted wilt, late

blight, and bacterial canker. These occur less

frequently, but occasionally they cause severe

damage. Good cultural practices will usually

prevent serious losses from nonparasitic diseases such as blossom-end rot, blotchy ripening, and puifiness. All these diseases and others

that affect tomatoes are fully described in

USDA Agriculture Handbook No. 203, "Tomato Diseases and Their Control."

NEMATODES

Tomatoes are subject to the attack of many

types of nematodes. These are minute, round

worms not visible to the naked eye. Roots of

the tomato plant may be attacked by the types

that live within, such as the root-knot

nematodes '^ and lesion nematodes ; * or by the

kinds that feed on the plant but do not entirely

enter the roots, such as the spiral nematodes ^

and stubby-root nematodes.** The root-knot

nematodes, however, appear to cause the most

damage.

Nematode damage on tomato plants is difficult to recognize, because nematodes do not

produce specific aboveground symptoms. Retarded growth, unhealthy appearance, wilting

during the hot part of the day or during dry

weather, or yellowing and stunting of the

whole plant may indicate the presence of large

numbers of nematodes on the roots. Roots of

plants suspected of being infected with nematodes should be examined.

The root-knot nematodes are the easiest to

' Prepared by Joseph M. Good, Nematologist, Crops

Research Division.

' Meloidogyne spp., formerly called Heterodera marioni (Cornu) Goodey, but now known to comprise a

group of many species.

* Lesion nematodes = Pratylenchus spp.

" Spiral nematodes = Helicotylenchus spp. and Rotylenchus spp.

" Stubby-root nematodes = Trichodorus spp.

recognize. They induce the formation of galls,

irregular knots, and swellings of the roots. On

the tomato plant these galls may be small and

hardly noticeable or large and irregular as

shown (fig. 19). When numerous, such nemaBN-36538

FIGURE 19.—Tomato plant infected with root-knot

nematodes.
30 AGRICULTURE HANDBOOK NO. 382, U.S. DEPT. OF AGRICULTURE

todes as the spiral, lesion, or stubby-root nematodes may cause stunted, short, or sloughed-off

roots.

Light, sandy soils are preferred by nematodes. Heavy soils also may be infested, but in

these the spread is much slower. Nematodes,

once established in a soil, are difficult to eradicate; therefore, every effort should be made to

prevent their introduction and establishment

in the greenhouse. Unfortunately, man himself

is the most effective distributor by transfer

of infected root crops and seedlings and by unclean implements. It is important, therefore, to

examine carefully the roots of tomato seedlings and transplants. Discard and destroy

plants with decaying and diseased roots, particularly those that have galls and swellings.

To produce clean tomato seedlings, it is best to

grow them in steam-sterilized soil, in soil

treated with a fumigant, in vermiculite, or in

peat moss.

If tomatoes must be planted in soil known to

be infested with root-knot or other nematode

pests, sterilization of the soil with steam or

with one of the newer soil fumigants or nematicides is strongly recommended.

Details of application procedures for soil fumigants and precautions on their use may be

obtained from manufacturers and distributors

of the fumigants, from State agricultural experiment stations, or from the United States

Department of Agriculture.^

INSECTS

A number of insects, mites, and related species may be serious pests of greenhouse tomatoes. Malathion or parathion greenhouse aerosols will control aphids, whiteflies, mealybugs,

spider mites, armyworms, the cabbage looper,

cutworms, and thrips. Parathion aerosols will

also control the tomato fruitworm, leaf miners,

and the tomato pinworm. Be sure to follow the

precautions and directions given on the container label. Some of these insects may be serious problems in early fall or late spring when

populations build up outdoors and move in

through open ventilators.

As with diseases, soil sterilization and regular sanitation practices do much to prevent serious insect problems. In combating greenhouse

insects it is always easier to practice preventive measures than to allow the insects

to become established and have to resort to

retaliatory measures. For information on specific control measures, consult your Agricultural

Experiment Station or your County Extension

Agent.

YIELDS

It is difficult to estimate the yield that can be

expected from greenhouse tomatoes, because

management plays such an important part in

the success of the crop. The grower's attention

to detail in maintaining optimum growing conditions and the prevailing weather conditions

throughout the season are reñected in the yield

of marketable fruit harvested.

Yields for fall and spring crops vary

greatly. A yield of 6 to 10 pounds of fruit per

plant can realistically be expected for a fall

crop, while 10 to 20 pounds of fruit per plant

can be expected for a spring crop. When two

crops are grown per year, a total yield of 24 to

28 pounds per plant-growing site is considered

excellent. This would equal more than 100 tons

per acre per year.

HARVESTING

It is important that tomatoes remain on the

vines as long as possible for them to be of the

' U.S. Department of Agriculture, Agriculture Handbook No. 286, "Chemical control of plant-parasitic

nematodes."

highest quality. Tomatoes continue to increase

in size and weight after they first begin to

show red color. Sugars and acids, which are important ñavor components, are also translocated into the fruit until they are fully colored.
COMMERCIAL PRODUCTION OF GREENHOUSE TOMATOES 31

The proximity to the market usually influences the stage of maturity at which greenhouse tomatoes are harvested. Fruits grown

for local markets may be allowed to remain on

the plants until they are near the full red

color. It may be necessary to pick tomatoes to

be shipped to distant markets as early as the

"breaker stage" or when the fruits first show

color on the blossom end. Plants are usually

harvested 2 to 3 times a week.

Greenhouse-grown tomatoes are usually harvested with the pedicel and green sepals or

calyx left on (fig. 20). This distinguishes

greenhouse tomatoes from field-grown fruits.

So that the calyx remains, the fruits may be

snapped from the plants or cupped with small

shears. When the fruits are snapped oif the

vines, the remaining stem is usually clipped

back close to the fruit so no stem protrudes to

puncture other fruit during harvesting, grading, or shipping. Clippers with short, rounded

blades are recommended so that the fruit is not

punctured.

Care must be taken not to bruise tomatoes

during harvest. The fruit should be grasped

with the palm of the hand and not squeezed

with the thumb or fingers. The harvested fruit

should be laid in the picking container and not

dropped. Bruises on harvested fruit may not be

apparent immediately, but they may show up

later and render the fruit unsalable.

Fruit may be harvested into small cardboard

or wooden baskets or plastic buckets. Many

growers use devices such as shown in fig. 21 to

reduce the amount of walking and carrying of

loaded picking containers. Some picking carts

are designed for movement between the tomato

rows while others are for use only on concrete

walks. In large greenhouses, small carts like

that shown are moved between the rows. The

filled baskets are transferred to larger hand

trucks on the main walks for transporting into

packing rooms.

To maintain the high quality of the product,

harvested fruit should be moved from the

greenhouse to the packing shed as soon as possible. The internal temperature of fruit allowed

to remain in the greenhouse increases as the

greenhouse temperature increases. Also, harvested tomatoes respire and release energy as

heat, so the internal temperature of the fruit

may reach 95° F. The higher the fruit temperature becomes, the more rapid the breakdown

of the tissues.

BN-36535

FIGURE 20.—Tomato with sepals or calyx remaining

attached.

BN-3663S

FIGURE 21.—Cart used to assist in harvesting

greenhouse tomatoes.
32 AGRICULTURE HANDBOOK NO. 382, U.S. DEPT. OF AGRICULTURE

GRADING, PACKING, AND MARKETING

The grading, packing, and marketing of the

harvested fruit culminates a large investment

in time and money required to produce a crop.

During these steps, proper handling of the

fruit is very important to retain its quality.

To slow down respiration reactions that

break down the sugars in the fruit, tomatoes

should be cooled to 55° F. rapidly after they

are harvested. This is especially important if

the fruit is to be held 8 hours or more before

marketing. Optimum storage conditions for tomatoes are temperatures between 55° and 60°

F. and 85 to 90 percent relative humidity.

Tomatoes may be sorted, graded, and packed

at individual establishments or at a central location shared with other growers. Federal

grade standards established by the United

States Department of Agriculture usually are

the basis for the sale and purchase of greenhouse tomatoes. The grades are based on quality and condition of the fruit. Although size is

not a part of grade, the size may be specified in

accordance with one of the following classifications, "Small" (under 3 1/2 ounces), "Medium" (from 3 1/2 to 9 ounces), or "Large"

(over 9 ounces). Complete information on

greenhouse tomato standards may be obtained

by writing to the Fresh Products Standardization and Inspection Branch, Fruit and

Vegetable Division, Consumer and Marketing

Service, U.S. Department of Agriculture,

Washington, D.C. 20250.

Greenhouse tomatoes are marketed in various types of packages. The most common package is a cardboard basket holding 8 pounds of

fruit (fig. 22). Other packages used include

larger cardboard baskets and various sizes of

wooden baskets. Some growers pack greenhouse tomatoes in small cardboard and cellophane containers.

Growers often wrap individual fruit in tisBN-36B34

FIGURE 22.—Greenhouse tomatoes packed in an

8-pound fiberboard basket.

sue paper printed with the words "Greenhouse

Tomatoes" and perhaps their brand name. Individually wrapped fruit reduces the spread of

diseases in shipping boxes and baskets and

identifies the product as being greenhousegrown. Another method used to identify greenhouse-grown fruit is to attach a decal or pressure-sensitive label to each fruit.

Several diseases or disorders may afi'ect harvested fruit. These diseases may lower the

market value of the crop or render it worthless. Agriculture Handbook No. 28, "Market

Diseases of Tomatoes, Peppers, and Eggplants,"

contains complete information on the subject.

Marketing may be directly to the retailer or

through a wholesaler. The volume of fruit

produced and location of the greenhouse influence the marketing procedures. A grower who

markets directly must assume some of the duties normally handled by the wholesaler. Regardless of the marketing procedure, premium

prices are paid for greenhouse tomatoes when

they are of high quality.

ii U.S. GOVERNMENT PRINTING OFFICE: 1970 0—387-596