This might not be the case, if you plant a late summer/early fall crop of hardy greens/roots. They go semi dormant during the darkest and coldest periods, but can overwinter and are harvestable all year if protected by a greenhouse, possibly with the addition of internal cold frames, and an extra layer of plastic rolled out at mid elevation in the greenhouse to further trap radiation.
I'm only supposing we could more effectively extend the radish/leafy-growing season more - not thinking the technique could enable us to grow veggies during winter (daily sunlight period is too short, etc)
Roberto pokachinni wrote:I think that the more they are massed together, the less surface area that will be exposed to cooling air as they will share an invisible envelope of warmer air around them in one location. On the other hand, if they were spread out, depending on your configuration, they might potentially be in better solar exposure positions to absorb solar radiation on their black surfaces.