Yes! A few feet below the surface, the soil is warmed by geothermal energy and maintains a constant temperature year round. The steady warmth of the soil a few feet below ground acts is a natural source of heat even during the coldest winters. Geothermal systems are designed to absorb this ever-present natural warmth and move it into our structures.
Even with free geothermal heat, it's still important to make sure that you retain as much heat as possible during cold winter nights. Make sure your greenhouse is tightly sealed against air leaks, and if you're in a particularly cold or windy climate, you may want to consider an additional insulating covering like thermal blankets to deploy at night or during cold snaps.
