Any ideas that will produce the desired result of successfully overwintering bananas in temperate climates immediately catch my interest. I think your intention to tap into the temperature of the earth has significant merit. I've previously posted picture of a simple device I've used to kickstart my plants in the spring, using otherwise discarded nursery pots. Going further with your idea, I might hammer two or three lengths of metal conduit into the soil inside the walls of my towers to tap into that latent heat. Additional to the whole conversation......there is no such thing as cold, per se, rather, the abscence of heat (sometimes a great abscence to be sure , lol), so the idea of insulation only has merit if trying to keep heat in, it will have less importance to keeping cold out (effective sealing is the trick here). So, maintaining and keeping a source of heat inside the enclosure certainly makes a lot of sense. Keep thinking, experimenting and sharing. We're all in this together..................
