It has gotten down to almost 0F inside my greenhouse, no heater used however the outdoor temperature has dipped as low as -9F.
Most of the stuff in the greenhouse still looks lively, and my greenhouse is a similar size to yours.
Even though daytime highs have barely gotten over 20F lately, the greenhouse is still breaking 50F on most days due to the stronger sun lately. Even when lows get down around 0F, it still lingers in the upper teens so the climate has clearly been changed inside the greenhouse. I do keep water barrels, plastic on the greenhouse floor and compost all throughout the greenhouse which gives off CO2 and provides heat. Elevated CO2 concentrations should help increase photosynthesis of the plants inside the greenhouse.
Here's the inside.
Barrels should be completely melted in another week. They have about 50% ice now.
It almost looks tropical in there despite it being completely white outside.
