“Wonder how well it works when it’s 5 degrees Fahrenheit with clouds everyday for two months”
We had worse than that and still we have a bumper crop of garlic, which we planted in September; strawberries, a perennial; and asparagus, which come up like weeds.
the trick was to cover everything with at least a foot of straw mulch... the first nice weather we had, those shoots were pushing through the top of the mulch like they couldn’t weight to get out...
our locale - just south of the cheddar curtain.
Lurking’
What if you ran a little plastic pipe under the ground, with some of the black portion above ground, all sealed, and let the sun slowly move warmer water through the pipes, just a sealed, passive system.