Dwayne wrote:

You could try it, but I would put some plastic gallon jugs in with the
seedlings. When the sun shines on the jugs, it will warm them up and keep
the seedlings warm during the night. You could paint them balck or dark
green to get more heat out of them. How warm, I have no idea. That will
depend on the size of the bed and area to be kept above freezing.

Dwayne

Or you can add a few ounces of manure to the water in the plastic jugs.
The manure dyes the water brown to absorb heat better and you will have
well aged manure tea in the spring for fertilizer. I grown lettuce and
cabbage all winter in temperatures down to 10F with no other protection
other then being surrounded by milk jugs. Inside a cold frame, you could
go much lower.

Lorenzo L. Love
http://home.thegrid.net/~lllove

“If you have a garden and a library, you have everything you need.”
Cicero