How Will the Greenhouse be Used?

What do you plan to grow in your greenhouse? Are you mostly interested in extending the growing season—seeding flats of bedding plants early in the spring and protecting them from frost in the fall? Or do you want to grow flowers and tropical plants year-round?

Your intentions will determine whether you need a heated greenhouse. Unheated greenhouses, which depend solely on solar heat, are used primarily to advance or extend the growing season of hardy and half-hardy plants and vegetables. Although an unheated greenhouse offers some frost protection, it is useful only during spring, summer, and fall, unless you live in a warm climate.

A heated greenhouse is far more versatile and allows you to grow a greater variety of plants. By installing equipment for heating, ventilation, shading, and watering, you can provide the perfect environment for tender plants that would never survive freezing weather.

How you plan to use the greenhouse will also determine its size, type, and location. If you only want to harden off seedlings or extend the growing season for lettuce plants and geraniums, a small, unheated structure covered with polyvinyl chloride (PVC) sheeting or even a cold frame—a glass- or plastic-topped box on the ground—might be all you need. If your intentions are more serious, consider a larger, more permanent building. A three-season greenhouse can be placed anywhere on your property and might even be dismantled in the winter, whereas year-round use calls for a location near the house, where utilities are convenient and you don’t have to trek a long way in inclement weather.