Composting bin

A composting bin is disclosed that is readily assembled from modular panels. The bin is made in superposed sections, each section being formed from ventilated sidewall modules assembled into a regular polygon, usually a square. A latching arrangement is provided at the ends of each sidewall module to unite it to adjoining modules. The sidewall modules have a double wall. An outer wall provides structural support and is preferably formed of spaced apart slats firmly mounted on a frame. The inner wall is formed from screening. Free air circulation is achieved through the spaces between the slats and screening into the interior of the bin. The sections are readily stripped from composting material held within the bin to allow ready access from the sides for removal or mixing.

BACKGROUND OF THE INVENTION 
The present invention relates to a bin for composting vegetable matter such 
as lawn and garden waste and to the method of its use. More specifically, 
the bin is of a type that can be readily assembled from modular parts and 
equally readily disassembled to permit quick and ready access to the 
contained composting material. 
Composting lawn and garden waste serves a dual purpose for the home 
resident. It provides a way to dispose of bulky waste such as lawn 
clippings, hedge trimmings, vegetable-type kitchen scraps, etc. Further, 
the resulting compost is a valuable soil amendment. It adds organic matter 
to the soil without imposing significant nitrogen or other nutrient 
demand. This is particularly important in sandy or clayey soils. The 
addition of compost improves tilth in heavy clay soils and water holding 
capacity in sandy soils. The organic portion of the soil also plays a 
critical function in ion exchange between mineral nutrients in the soil 
and plant root structures. 
Compost formation is caused by bacterial and fungal action, especially on 
the cellulosic and other carbohydrate portions of the plant residues. It 
can proceed under either moist aerobic or anaerobic conditions, although 
the former is much to be preferred. Thermophilic and other aerobes are 
particularly efficient at reducing plant wastes to a rich humus. Aerobic 
decomposition generally proceeds much faster and is essentially without 
odor. Depending on a number of factors, plant wastes can be composted 
under highly aerobic conditions in periods ranging from a few weeks to 
several months. This same process with similar vegetal matter can take 
years under anaerobic conditions. Aerobic composting results in emission 
of water and carbon dioxide with considerable heat being produced. 
Temperatures in actively composting plant wastes can rise to levels in the 
neighborhood of 65.degree. C. (150.degree. F.) or even higher. Some of the 
composting microflora are adapted to thrive and multiply under these 
elevated temperatures. The higher temperatures are very desirable because 
the composting action is greatly accelerated and weed seeds and plant and 
soil pathogens are killed. 
Since compaction occurs as a compost pile builds up and as material 
decomposes, aeration tends to become poorer, especially in the interior 
portions. In these compacted volumes the action of the obligate aerobes 
causing the composting slows significantly. Ultimately the aerobic 
microflora would be replaced by anaerobic microflora. These not only act 
slowly but give off methane and obnoxious gases containing reduced sulfur 
compounds. Serious home gardeners usually ensure good aeration by 
periodically turning over the composting material to restore a loose and 
permeable structure. This might be done several times during the 
composting period on a given pile of plant wastes. It is a general rule 
that, within reason, the more times an active compost pile is turned over 
the faster the process will proceed and product uniformity will be better. 
The serious gardener will manage the bed and determine turnover times by 
measurement of the internal temperature profile over time, according to 
known procedures. Unfortunately, for the average gardener turning over a 
compost pile involves relatively heavy work and considerable lifting. 
Normal bins are usually a rectangular wooden structure that may or may not 
have one open or partially open side. As the composting material is 
shoveled or forked out, access to the material in the bottom becomes 
difficult. Some existing bins are made with hinged sides so that the bin 
can be completely stripped from the pile to enable easier turnover. These 
tend to be heavy and awkward and have not found general acceptance. Other 
strippable bins are made of wire screening, such as poultry wire. This is 
prone to deformation during use and kinking upon removal. These screen 
bins do permit better aeration than closed-sided bins but suffer from 
accelerated moisture loss which slows composting. 
Commercial composting operations have long been in operation to produce 
growing medium for crops such as mushrooms. These formerly used large 
quantities of animal manures. More recently they have used other 
agricultural wastes such as corn cobs and stalks, surplus or spoiled hay 
and similar plant materials, as well as sludge from bioponds. These 
materials are usually piled in long windows on the ground and frequently 
turned with large machines to ensure good aeration. A machine of this type 
is shown in U.S. Pat. No. 3,856,276. 
Many types of home composting bins have been proposed and some are sold 
commercially. U.S. Pat. No. 3,654,903 describes equipment for growing 
earthworms and simultaneously producing a compost leachate, commonly 
called "compost tea". This system would seem to be poorly adapted for the 
gardener growing anything more extensive than house plants. 
U.S. Pat. No. 3,951,294 describes a compost bin composed of interlocking 
modular units that slide together vertically. The sidewalls may be 
perforated or may be constructed from screens held in marginally located 
frames. These frames interlock side-to-side by sliding together 
vertically. They can also be built up in a one-above-the-other fashion 
using a pin and socket locking arrangement. A related divisional patent, 
U.S. Pat. No. 4,125,394, shows one version that apparently has a snap-on 
lid. 
U.S. Pat. No. 4,105,412 describes a composter which again is primarily 
adapted for making a compost tea or "sap". The composting plant material 
is held within a perforated corrugated structure which is surrounded by an 
imperforate shell similar to a bottomless garbage can. A tight lid covers 
the device. Water is periodically poured through the composting plant 
waste and the "sap" is collected in a pail underlying the upper portion of 
the structure. While the preferred embodiment would be essentially 
anaerobic, one version shows a structure of simple spaced apart horizontal 
wood slats resting on the bottom pail. One of the bottom slats may be 
omitted to permit "mining" the compost after it is formed. 
U.S. Pat. No. 4,184,602 shows a modular multipanel system useful for 
storage of grain or other materials and also useful for composting bins. 
Two identical panels are hinged along their edges. The panels have 
regularly spaced notches along their upper and lower transverse edges. 
These notches serve to accommodate clips that can combine the panel 
modules into various configurations. 
A simple enclosure of wire screen panels is shown in U.S. Pat. No. 
4,211,033. The panels are relatively rigid and self supporting and can be 
formed into enclosures of various shapes and sizes. 
U.S. Pat. No. 4,352,888 describes another modular composting bin made of 
molded plastic panels. These are joined end-to-end by vertically sliding 
together a molded rod and hook arrangement. Slots are provided in the 
sidewalls to provide limited aeration. Telescoping flanges on the top and 
bottom of the panels provide a snap together arrangement for increasing 
the height of the bin. There is no ready provision for removing compost 
except from the top. 
U.S. Pat. No. 4,683,674 shows a composting bin of modular molded plastic 
units similar in many ways to the one just described. Provision is made 
here for doors on the sides of the panels. These ostensibly permit removal 
of compost from any level although, depending on the size of the bin, this 
would be difficult using any tool larger than a garden trowel. The doors 
seem better adapted for use of the bin as a vertical planter. One figure 
shows an entire lower panel absent for compost removal from the bottom. 
How this panel would be removed, in view of the interlocking construction, 
is not described. 
A simple wood frame supported screen wire enclosure that can be readily 
opened to give access to the composting material is described in a Pierce 
County (Washington) Master Gardeners Bulletin. In principle this is 
similar to the enclosure of U.S. Pat. No. 4,211,033. While simple wire 
containers of this type can ultimately produce compost, the exterior 
portion of the pile is exposed to ambient air and wind which results in 
rapid heat and moisture loss from the surface. This can be sufficient to 
slow or almost stop aerobic composting action. On the other hand, bins 
made of wood, plastic, or metal frequently inhibit access by fresh air to 
much of the surface of the composting mass. This can result in an 
anaerobic environment within the stack of material. 
A number of commercially available or home made composters use a tumbling 
or rotary action to speed the composting process. Several of these are 
compared with stationary composters in an article by Charles Nardozzi, 
National Gardening, Sep./Oct. 1991, pp 38,39, and 65. Most of these are 
small and of very limited capacity. 
While all of these prior known composting bins would have greater or lesser 
usefulness, none of them fully address the problem of simplifying the 
turnover of substantial amounts of the contained composting plant material 
to achieve rapid aerobic composting. The present invention is particularly 
well adapted for dealing with the problem of compost turnover and for 
making compost very rapidly and efficiently with considerably reduced 
manual effort. 
SUMMARY OF THE INVENTION 
The present invention relates to a composting bin and the method of its 
use. The bin is of simple modular construction and is readily assembled 
and disassembled without the use of tools. It is particularly well adapted 
to be stripped level-by-level from a contained stack of plant material to 
enable rapid and easy removal or turnover of the contained composting 
plant wastes. 
The bin itself is composed of a plurality of sections stacked or superposed 
vertically one upon the other. Normally the height of the sections will be 
chosen so that a stack of three sections will be optimum. However, a 
greater or lesser number might be chosen for particular situations. Each 
of the sections is assembled from a plurality of individual sidewall 
modules. These are assembled end-to-end into the form of a regular 
polygon. Most typically the configuration chosen will be for a square bin 
but other geometries, such as hexagonal, may also be selected. 
Each of the sidewall modules is of double layer construction. The outer 
wall layer will be rigid for structural support. It is preferably composed 
of either vertically or horizontally spaced apart slats rigidly mounted on 
a frame. While wood is a preferred material of construction, other 
materials, such as molded or extruded plastics, are also suitable. The 
outer wall may also be made from solid panels, such as plywood, as long as 
sufficient ventilating apertures are provided. In addition to providing 
structural support, the outer wall provides sun and wind protection to 
prevent the composting material from excessive drying. The inner layer 
will be an open mesh screen. This may be made of woven or welded wire or 
plastic screening. Perforated sheet metal or plastics are equally suitable 
and should be considered fully equivalent to screening and to be 
encompassed by that term. While this is not critical, it is much to be 
preferred that the screening should have at least 50% open area. The inner 
wall layer is made of screening and is spaced apart from the outer wall 
sufficiently so that good air circulation occurs between the walls and 
through the screening material. The slats in the outer wall layer should 
be spaced apart sufficiently so that air is readily admitted between them. 
Each sidewall module will have an external latching mechanism, located at 
each end, for joining the adjacent modules together. Many types of latches 
are suitable. One that has proven excellent is the simple loop and hook 
lever latch of the type used on luggage and carrying cases. Similar 
latches may be used on the longitudinal or transverse edges of the modules 
for joining the superposed sections in proper geometric and mechanical 
alignment. 
Latches on the longitudinal edges are only one of a number of possible 
forms of vertical alignment mechanism for the bin. Another is the use of 
bars which are vertically oriented; i.e., normal to the transverse edges 
of the modules. These are fixed to either the outer or inner walls of the 
modules and extend beyond one or both of the edges to engage the adjacent 
upper or lower module or modules. Normally a single vertical bar on each 
module will be sufficient for alignment although more may be used if 
desired. 
In use, the modules are assembled into sections and the sections are 
stacked to the desired height to form the completed bin. The bin may be 
placed either on the ground surface or on a prepared basal platform. It 
may also be slightly elevated on corner blocks. Plant waste to be 
composted is accumulated until the bin is approximately full. The newly 
added material may be inoculated, if desired, with old compost to expedite 
microbiological action. After a sufficient period of time for composting 
to have commenced the bed may be turned over to ensure good porosity and 
aeration and to accelerate the action. This is most conveniently done as 
follows. The uppermost section of the bin is disassembled so that it can 
be easily stripped off of the column of partially composted matter within 
the bin. This section is reassembled on the ground beside the original bin 
and becomes the lowest section of a new bin. Material from the top is then 
shoveled and pushed from the column of partially composted plant waste 
into the reassembled bin section. Then the middle section is stripped from 
the remaining original compost column and reassembled on top of the first 
removed section. Access to this compost column is from the sides as well 
as the top. Again, the compost from the middle portion of the first bin is 
shoveled into the new bin. The required lifting distance is almost 
negligible, being no more than the height of one section. Finally, the 
process is repeated for the last section of the original bin. In essence 
the column of partially composted material has been turned upside down but 
with considerable mixing and loosening also occurring. 
One version of the composter will include a lid or cover coextensive with 
and covering the upper section. A preferred cover is made in two parts. 
The lower portion of this cover is comprised of a peripheral frame 
supporting a screen in the interior area. A second part is a solid panel 
which covers the screen. When the bin is stripped down the lower portion 
of the cover may be placed on a reassembled section for screening finished 
compost. The cover protects against excessive drying from sun and ambient 
air movement as well as excluding pests. 
It is an object of the present invention to provide a composting bin that 
is readily assembled and disassembled. 
It is another object to provide a composting bin that allows excellent 
aeration of the contained composting plant wastes while still reducing 
moisture loss through evaporation. 
It is a further object to provide a composting bin that allows easy turn 
over of the contained materials in order to promote rapid composting. 
It is also an object to provide a composting bin that is compact and 
attractive and does not detract from the appearance of a well kept urban 
lot. 
It is yet an object to provide an essentially odor free method that can 
very rapidly form composted plant material. 
These and many other objects will become readily apparent upon reading the 
following detailed description taken in conjunction with the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present composting bin is advantageous from a number of standpoints. It 
can be made large enough to hold a critical mass of composting plant 
wastes yet is efficient in the use of space. It reduces the labor required 
for turning over and mixing significant amounts of composting material. 
Further it may optionally have a lid or cover that protects the contents 
and can serve as a convenient screen for removing uncomposted sticks and 
similar material from otherwise finished compost. 
There are several requirements for rapidly and efficiently producing 
compost. The mass of plant waste must be large enough so that there is not 
significant heat loss, especially from the interior portions. In general 
this requires a volume of at least about 1 m.sup.3 on a base of about 1 
m.sup.2. Adequate moisture must be present and provisions must be made 
either to prevent moisture loss or to periodically add water. The 
composting mass must be sufficiently loose or porous to permit entry of 
air into the interior but airflow should not be so great as to cause 
excessive drying or cooling. Finally, a healthy colony of suitable aerobic 
bacteria and fungi must be present. These will be present naturally on 
much of the plant waste added to the bin but the action can be accelerated 
by seeding newly added material with previously formed compost. 
Reference should now be made to the drawings where construction of a 
preferred embodiment of the bin will be described. FIG. 1 is a perspective 
view, taken from above, of two sections of a partially assembled 
composting bin. Normally there would be a third or even more sections 
stacked on top of these, although this is not absolutely essential. The 
bin, generally shown at 2, comprises a lower section 4 and a superposed 
section 6. Each section is composed of four identical sidewall modules 8 
joined at their ends by latches 18, 18'. An alignment bar 16 is placed at 
one end of each module comprising section 6 to hold it in vertical and 
horizontal register with lower section 4 and any upper sections 7 that 
might be added. These bars may be located at any position on the module 
and more than one may be used if desired. Latches similar to those uniting 
the ends of the sidewall modules, or a pin and socket arrangement, may be 
used in place of the alignment bars for vertical assembly. 
The bin may rest directly on the ground or another surface. It is sometimes 
preferable to support the corners on concrete blocks, bricks, etc. 20 so 
that the lowest section in not in contact with soil. 
Construction of the individual sidewall modules is best seen in FIGS. 2-5. 
One preferred construction uses spaced apart vertical wooden slats 10 
fastened to transverse frame members 12 by screws, nails, staples, or 
other means. These form the outside of the sidewall module and provide 
structural rigidity and integrity. The spacing should be sufficient to 
provide free flow of air between the slats. Materials other than wood; 
e.g., molded or extruded plastics, may be used for the outside portion of 
the sidewall modules. Alternatively, they may be constructed using a 
panel, such as plywood or water resistant flakeboard which is provided 
with sufficient apertures for ventilation. Normally the open area of the 
sidewalls should be at least about 10% of the total area. 
A screen 14, of metal or plastic, is mounted on the opposite side of frame 
members 12. This is spaced apart from the outside slats to leave an air 
space 15 and forms the interior surface of the sidewall modules which will 
be in contact with the composting plant material. The screen allows good 
air circulation into the mass of composting material and should have at 
least about 50% open area for best results. Screen 14 should be spaced at 
least about 1 cm from the material forming the outside wall to allow 
unrestricted air circulation. Construction of the type described permits 
good air circulation around and into the composting plant material but 
prevents excessive moisture loss due to the action of sun and wind. 
While dimensions of the sidewall modules are not critical, a length of 
about 1 m and height of about 40 cm for each sidewall module has proved 
convenient. When stacked three high, a bin of these minimum dimensions 
provides sufficient volume to reduce heat loss and provide and maintain a 
favorable thermal and moisture environment for the composting 
microorganisms. 
As seen best in FIG. 6, each end of every sidewall module is provided with 
a latching arrangement for attaching the module to the adjoining modules 
in any given section. These latches may be of many different types 
including sliding bolts, hooks and eyes, etc. One that has proved very 
useful is a trunk-type latch employing a loop and tightening lever 18 
which engages a corresponding hook member 18'. 
While not absolutely essential to the construction and operation, a cover 
or lid forms a very useful complement to the composting bin. One such 
cover, designed to serve a dual purpose, is shown in FIG. 7 where it is 
shown in place on a single bin section 7. The cover can serve to retain 
moisture in the composting mass by preventing drying from the action of 
sun and wind. Further, it helps to maintain an optimum moisture level by 
excluding rain. It also helps to keep out small animals and other pests 
that might be attracted; e.g., to kitchen scraps. The cover shown consists 
of a lower portion 22 and upper portion 24. The purpose of this two piece 
construction will be described but it is evident that any form of cover, 
such as a plywood panel, would also be suitable. 
In the preferred version of cover, lower cover portion 22 consists of four 
wooden members 26 joined together into a square frame reinforced by corner 
gussets 28. A screen member 30 is attached to the underside of the frame. 
The upper cover portion 24 is sized to fit closely within the confines of 
the frame formed by members 26 and may rest upon the screen 30. 
Alternatively it may be made somewhat larger; e.g., with flanged edges, so 
that it rests on the interior edges of the frame describing lower portion 
22. 
Still referring to the arrangement shown in FIG. 7, it will be apparent 
that the lower cover portion 22 can serve to screen the finished compost 
to remove any uncomposted material such as twigs or branches that do not 
readily decompose. In this case the cover is placed over an empty bin 
section 7 which receives the screened compost. While this would ordinarily 
be the uppermost section removed from an assembled bin, other forms of 
support for the lower cover portion 22 that give sufficient ground 
clearance would be equally suitable when it is used for screening. 
FIG. 8 shows how the present composting bin is advantageously used for 
preparing compost on an accelerated schedule. Normally a bin of three 
stacked sections will be filled with plant material which is allowed to 
compost for a period of time. The particular usefulness of the modular 
construction of the individual sections becomes readily apparent at this 
time. It would be very difficult, even for two people, to lift off a 
unitary section from the top of a compost filled bin. This is because the 
composting plant material tends to lock into the openings of the screen 14 
forming the inner wall of the sections. By simply releasing the latches 18 
at the ends of each sidewall module, the sections may be readily stripped 
away from the contained compost. At any desired interval the upper section 
7 is disassembled from the bin and reassembled adjacent to it. A column of 
compost 34 then remains standing above the middle section 6. The portion 
upstanding above section 6 is easily shoveled or pushed into the now empty 
section 7 where it is loosened and mixed. Next the sidewall modules of 
middle section 6 are stripped off and reassembled atop section 7. Again, 
the compost is shoveled from the original column into the newly emptied 
section 6. Finally, the original bottom section 4 is stripped and 
reassembled as a new top section. The compost located therein is shoveled 
onto the top of the newly turned over and mixed pile in the reassembled 
bin. Lifting during shoveling is greatly reduced by this procedure. It is 
a further convenience that it is not necessary to try to shovel compost 
out of a bin with inconveniently high walls. 
During composting the volume of material is significantly reduced, often to 
about 1/3 of that originally present. The present construction thus 
enables one or more sections to be removed as composting proceeds. These 
can be reassembled into another bin and used to accept new material so 
that it need not be added to essentially finished compost. 
When placed in a simple pile it can take anywhere from 6 to 24 months for 
plant material to decompose to the point that it can be used as a soil 
additive. Using the present composting bin, a mixture of lawn clippings, 
wood shavings, and garden weeds was converted into ready-to-use compost in 
only three weeks. The newly added material was initially inoculated with 
finished compost and then turned over three times during composting. 
Internal temperatures as high as 65.degree. C. indicated vigorous action 
of the aerobic microflora. 
The modular construction of the present bin is advantageous in that it 
enables very compact packaging for sale and storage. 
While the description just given is of the best mode presently known of 
making and using the composting bin, it is readily apparent that many 
variations not shown or described could be made without departing from the 
spirit of the invention. Thus, the invention should be regarded as limited 
only as it is described by the following claims.