I was in need of an outdoor place to keep a few pineapples alive through the winter so I decided to build a greenhouse. It is a 4'x5' structure that is about 5.5' tall. I built it with a 2x4 frame and covered it with two layers of 3.5 mil plastic, on on the inside and one on the outside of the frame. The problem I am having is that it is not retaining any heat throughout the night and the temperatures are equaling the outside temps which was 26 last night. I have made sure all seams are taped and do not see any obvious holes in the plastic. I also added some foam insulation board the the north wall and the floor. I also have four 5 gallon buckets filled with water to act as a thermal mass. I have watched the temps come up as high as 98 inside but they soon drop and just does not seem to retain any heat. I am not concerned with it staying 65-70 degrees throughout the night but would like it to stay 45+ and really protect the plants from frost. Any suggestions to retaining heat would be greatly appreciated.
