Winter in Montana can be a very cold experience. Karl and I were in San Diego, Calif. in Nov 2014 and the first cold snap of the season came unexpectedly. It was a -17F and we were in San Diego, there was nothing I could do. I had my inner greenhouse up and a heater in the greenhouse. But the power had gone off so the heater would not restart. I just KNEW everything in the greehouse was frozen solid. I was amazed when I checked the greenhouse. NOTHING had died! My tomato tops had wilted back, but that was the worst of the damage.
So how did this happen and what did I have set up?
First it is important to understand how the greenhouse is laid out. The pit greenhouse is in the ground. The back wall is 11 feet tall. About 2 feet is above ground. The front of the greenhouse is not underground. It is like a daylight basement. To keep the heat in I put up a inner greenhouse and keep the plants against the back wall as much as possible. What is an inner greenhouse? I build a frame inside the greenhouse and put a layer of plastic on it. I do my best to keep it air tight.
Now, in addition to the back wall I work to help retain heat, I have 3 – 55 gallon drums of water. The barrels are dark green to absorb the heat but not let algea grow.