High Tunnel Gets Colder Than Outside

[Cole_Robbie]

A year and a half later, and I am still pondering the initial topic of this thread, especially how to avoid the inside of the greenhouse getting colder than the outside. My best guess right now is humidity. I have troughs and bins of water through my greenhouse. You can see in the pic below, I sprayed down the gravel a little as well when I was filling the bins. Outside temperature was in the 40's, and it was almost 90 inside, and more importantly very humid. Condensation forms on the inside of my plastic. The layer of water droplets has a nice diffusing effect on the daytime sunlight, but I also think it adds an insulating value, and possibly even a shield against atmospheric cooling radiation. The humid air may help, too. The cold air outside is very dry.

Lows have been around 30 the past few nights. All of the outside tender plants froze. I have a few ghost pepper plants with my greenhouse mums. They can be my canary in the mine shaft as far as plants freezing. I'm not using any heat, and my single layer of old plastic is far from perfect, but so far, so good in the low temperatures.