I am on my second make-shift greenhouse, gradually working my way up to something that I don’t have to MacGyver, however, I am not there yet. The last 3 years I’ve managed to keep a zippered vinyl 3’x5’ “greenhouse” from freezing in a northern Washington winter, but I now have an actual twin-walled 6’x8’ structure and need some knowhow on the best way to heat it.
For the 3’x5’ I used a 5 gallon pail of water with a pail heater. The electrical ran under the vinyl wall and plugged in to an outlet adapter that turned on at 35* and off at 45*. This kept the ambient temperature in the small structure from dropping below freezing, although we did not have extremely cold winters in those years.
Can anyone make suggestions for my slightly upgraded circumstances? This greenhouse is for those trees that do need some cold for dormancy, but are not quite up to snow, and freezing temperatures, even with root protection.