I went out to my cold-house, last night, to pick arugula for our salad. We have been having a visit from some Arctic air and the outdoor temperature was in the low teens.
I use the two layer method of protection in my cold-house. The outside layer is the hoop-house skin, itself, with a second, inner layer of plastic sheeting held a few inches above the plants. No need to water anything under these conditions. the water that does evaporate, condenses on the plastic and falls back down after a while. At deep winter temperatures during the shortest days of the year the plants don’t do much growing, anyway.
As I lifted the inner sheeting to pinch off a dozen leaves the frozen condensate on the inside of that sheeting crackled and rained down on the plants. I went back into my kitchen with leaves that were clearly partly frozen and put them in the sink. By the time I was ready tear them up into small pieces for the salad, they were defrosted. Some were translucent, at places, but looked ok and tasted fine.
I checked my remote readout of the wireless thermometer probe that was still out in my cold-house arugula bed. It read 20.4 degrees Fahrenheit.
Today was a warmer, sunny day. The cold-house bed temperature was a balmy 58 degrees. No ice on the inner plastic sheeting and the plants all looked just fine, revealing no apparent damage from the cold nights.