How effective do you think a low hoop poly-tunnel is, as a cold frame?
Assuming the long axis ran East-West.
Does a cold frame totally need the bottom 6-10" as an insulator like thick wood? It always seemed to me that, with a low sun angle, that would guarantee shade when plants most needed light and warmth.
I set up some low hoops, then a tent, where I had a bed I wanted to keep warmer. It was a somewhat sunny spot in the summer, but NOT in January! I can confirm that a mostly-shady plastic-film tent is indeed a COLD cold frame.
(But sealing some leaks better might at least get the forst to melt off the film faster!)
