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Mel and black and clear plastics

Square Foot Gardening List - http://www.flinet.com/~gallus/sqft.html

I have been wondering about Mel's statement in his book (p.119) not to use
black plastic for temp raising. He says it's been proven that the soil
temp under it is not raised as previously thought,that only clear plastic
can raise soil temp,that black plastic creates a lot of heat but stores it 
in the plastic itself, and that that heat is then radiated upward at
night,warming the plants but not their roots.Many of my organic gardening
books (e.g. the ones published by Rodale), with later publishing dates
than Mel's book,still claim that black plastic raises soil temp,tho not 
as high as clear plastic does, and
is better to use for this purpose in southern climes (I'm in Alabama) so
that the temp isn't raised excessively. Does anyone know the source of the
"proof" that Mel refers too,or know the definiive facts of the matter?

Second question:is there any harm in transplanting my corn salad and
miner's lettuce (mache and claytonia), both very cold hardy, into black
plastic now? We're still having day temps around 70 and nights in the
50's. Soil temp about 70. I wouldn't want them to fry while sitting on the
plastic-I don't know if it would make a difference if they're growing thru
slits in it, or if I enlarge holes around them so they don't touch the
plastic at all. They receive close to 3 hours of direct sun,12-3 p.m..

Third question. I've made a large version of Mel's sunbox. For warmth 
later in the winter, I was thinking of putting plastic milk jugs filled
with water inside the box.. Similar to my first question, some books
recommend painting these jugs black, so I was wondering if the clear jugs
or the black jugs would raise the temp more.

Hope someone can help me!
Thanks,
Peg Daniels
daniemm@mail.auburn.edu


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