Q: I am thinking of building a greenhouse. Can I do geothermic heating and use warmth from the soil to keep citrus trees alive?
A: It’s theoretically possible to use geothermic heating or cooling but I don’t think you’ll find it cost effective. You’ll need several thousand dollars’ worth of pipe, pumps, heat exchangers and fans to extract enough heat to be useful. The greenhouse will have to be extremely tight and well-insulated. Even with propane as high as it is, you can buy a heater and keep a small greenhouse comfortable in winter for a few hundred dollars.