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 we could do. We had the inner greenhouse up and a heater in the greenhouse. But the power had gone off so the heater would not restart. We just KNEW everything in the greenhouse was frozen solid. We were amazed when we checked the greenhouse. NOTHING had died! The tomato tops had wilted back, but that was the worst of the damage.
So how did this happen and what did we 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. Our goal in this design was to use the heat of the earth to help warm the greenhouse in the winter.
To help keep that heat in we put up a inner greenhouse and keep the plants against the back wall as much as possible. What is an inner greenhouse? We build a frame inside the greenhouse and put a layer of plastic on it. We do our best to keep it air tight.
Now, in addition to the back wall we work to help retain heat using several 55 gallon drums of water. The barrels are dark green to absorb the heat but not let algae grow. We do not have running water in the greenhouse so we use the water from one of the tanks during the winter. We are always amazed at how little the plants need water in a closed system.
Note: The image ‘zones’ are used in our RaspberryPi Greenhouse Monitoring System. More on that later.