The more you have in there, the better it will hold heat.Pots in the green house are all planted. About 60 tomatoes, some other stuff. It was warm up there while I was in there, as the sun was shining. As long as we have some sunshine, it'll be nice in there.
I stuck the thermometer in one pot... 72 ° in the dirt. It won't stay that warm, but I don't know how quickly it cools off.