They practically grew themselves in those houses, I didn't do a lot past that! I think it's the passive-solar design that made the difference, I have a book that describes ways to trap and manage the radiation that naturally builds up in the right conditions. 

A sheet of plastic over a frame with a big rock in the middle to soak up sunlight and slow-release and radiate that back on the plants into the night, is my version of passive solar heating, and it did work well enough for this region, this year.