I'm hoping some of you that have grown in cold frames and/or hoophouses can shed some light on this for me.
I just can't wrap my head around how a cold frame or hoop house helps you grow things over the winter. I get how it warms it up nicely during the day. Got that. But it won't hold in enough heat at night to keep common cold crops from dying. Temps inside are maybe 1-3 degrees above what they are outside overnight. They may have protection from direct frost, but effectively none against temperatures. I've tried lettuce and broccoli that both died in low 20's temps. I have one friend that has a cold frame, but they bring their plants in the house if its going to be really cold overnight. But I know people say they grow/keep things in there all winter. Over the winter we commonly get overnight lows in the teens and occasionally in the single digits.
If someone could help explain how it keeps plants from dying from extreme cold overnight, I'd love to understand! People say they grow with these methods over the winter and it bugs that I can't seem to understand how it works.