A combination of passive and active heating methods is a very good way to maintain a stable temperature in small greenhouses during winter. For passive heating, incorporate thermal mass like water barrels, stone, or bricks inside the greenhouse. These materials absorb heat during the day and release it at night, reducing the need for supplemental heat.
For active heating, an electric heater or small space heater can be used, ensuring the greenhouse maintains the desired temperature. Choose a heater with a thermostat for consistent control. If the greenhouse is very small, a small propane heater or a ceramic heater can be sufficient. Insulating the greenhouse helps keep heat in, so use bubble wrap, double glazing on windows, or a condensation-resistant greenhouse cover, and ensure that gaps and doors are sealed.
