To those of you that use unheated structures to over winter
Ok so I have a small green house made out of plastic that is just barely big enough to walk in to and move around a little in. If I don't use a heat source what are ways that will still allow natural heat/sun in but keep it above freezing as well? I'm thinking about experimenting to see how much a coconut palm will really need to survive a winter here using as little as possible before actually spending a lot on a heated green house.
What makes me think it might be possible is the fact that in an enclosed area that allows sunlight in the temps can easily be 10-20f above air temps outside on sunny days. Even though our winters are mostly cloudy we still get a fair amount of sunlight. That should be just enough to get the palm through until the weather warms up. That is if the night time temps can be kept above freezing and warmer than each nights low since they are on the cool side. So what are ways to keep them up? Or would I have to wrap the palm with a frost cloth on nights with a frost warning?