From: klier@iscsvax.uni.edu
Newsgroups: rec.gardens
Subject: Re: Proper lighting for houseplants?
Date: 23 Aug 92 19:35:42 -0500
Organization: University of Northern Iowa

ahill@boi.hp.com (Andy Hill) writes:
> We're in the process of building a house, and have, in the plans, a plant
> shelf around the kitchen on top of a 8' partial wall with a vaulted ceiling
> above it.  All plants will be somewhat hardy (pothos, ivy, etc.)
> 
> My problem is that I can't figure out how we're going to be able to get
> enough light to the plants to keep them happy (I'd rather not have to hassle
> with a 'rotate to windows' schedule).  The only two possibilities I've been
> able to come up with are: (1) lots of incandescent (ugh!) lights above the
> plants, or (2) strips of grow or cool+warm fluorescents along the base of
> the shelf (hidden from view), essentially lighting the plants from below.

Incandescents will fry your plants before they give them enough light.
Fluorescents are probably your best choice, but I've never mounted them
*under* plants before.  Remember-- plants grow toward light...

Most foliage plants will tolerate 250 ft-candles of fairly decent
fluorescent lighting (like grow lights or cool+warm tubes).  Generally
takes 350-650 ft-candles to get the common flowering houseplants to bloom.
There is a method in the Time-Life Foliage Houseplants book for calculating
ft-candles using a camera's light meter, but I don't have the book in
hand at the moment-- it's part of my peripatetic library...

I generally use the following guesstimations for light-gardening:
use at least 2 tubes; min 15-20 watts/sq ft foliage, tubes 6-12"
from top of plants.  I also try to have the area around the plants
painted white, for maximum reflectance of light.  Most species need
12-16 hours of light AND THEY NEED A DARK PERIOD.   Too much daylength
can be fatal.

Then watch the plants.  If new growth has about the same density of leaves
and same sizes of leaves as on the greenhouse-grown portion of the plant,
you've got it about right.  If the leaves are smaller, or the internodes
are significantly longer on the new growth, you need to think about 
more light or a plant that tolerates darker conditions.

I think you're right to start with some pretty rugged species like
Pothos, Philodendron, maybe shrimp plant (Beleperone guttata), etc;
If they don't grow, you _know_ you need more light.  

A couple of other ideas:  Would it be possible to suspend fixtures
over the plants from the ceiling?  You could add custom wooden or 
sheet metal reflectors to avoid the "warehouse look" of bare fluorescents
or plain shop lights.

You can also pull the ballasts from fluorescent fixtures and rewire them
to locate the ballasts elsewhere if heat and/or ballast hum is a problem.

How are you going to water these 8 ft up?  Capillary matting might be
a good investment in this case...

IMHO, the best book I've seen on gardening under fluorescents is
Brooklyn Botanic Garden.  1970.  Gardening under Artificial Light.
Even new, the BBG handbooks are less than $5 around here, and I often
see them at used book stores.

I've been redoing my office a bit this weekend, moving some bookcases
to avoid the waterfall that develops inside every fall from the roof that
*can't be fixed*, and I got a wild hair to use some of the bench space
in my office to grow some plants.  I've laid shiny white plastic-coated
paper on the surface of the black bench, and positioned more behind 
as a reflector.  Under the cupboard over the bench, I've mounted 2 double-
tube 4ft fluorescent fixtures-- and I'm guessing I'll probably take it up
to 3 fixtures, and maybe a 4th or 5th behind, with a diffuser panel.

At the moment, I've got the Paphiopedilum and Haemeria orchids that have
been summering in the shade of the front porch.  I'll probably go over
to the greenhouse later this week and mooch some throw-outs.  I'll let
you know how the project progresses... 

Kay Klier

(and please, never let me find out who designed a biology building with
*NO WINDOWS* in any lab, classroom or office.)