Pit Greenhouse ~ Winter Decisions

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.    

Oct 26, 2015
My granddaughter and I worked on the inner greenhouse frame work today.  We used 1" PVC to create the rame.  Then we added the plastic.  The goal is to keep the frame work up year round once we have a structure that works for us.  Then when cool weather shows up it will be a matter of rolling down the plastic.