Melissa:
I've been bothered by your statement to the effect that you have this plastic, zippered cold frame (Is it the one that is sold by Lee Valley Hardware?) on your
deck .
One of the major purposes of a cold frame is to isolate the trees from temperature fluctuation by taking advantage of the insulation provided by the ground.
I have my portable cold frame on a brick terrace in a very sheltered (from both light and wind) portion of my house.
If I had to use it on a deck, I would want to provide some insulation under the trees. The trick would be to get something that would drain. My best guess would be to break up a bale of straw into slabs. Of course, if you live in a condo or apartment, the folks who run it will probably "have a cow" about that, so you might want to be somewhat discreet.
