Garden greenhouses offer a great way to enjoying gardening year-round, especially in areas with cold winter climates. Greenhouses give gardeners a head start on the growing season as well as a place to grow plants all winter long. Planning remains the key ingredient to building a greenhouse that meets all of a gardener's goals.
The first step in preparing to add a greenhouse requires knowing how many plants the greenhouse needs to hold. Then, look at how much bench, work and storage space to include to meet those needs. Gardeners should also keep in mind any possible expansion plans down the road.
The greenhouse needs a location with plenty of sunlight, especially in the morning. Consider south-facing sites where morning sunlight hits the area on the east side. This location also gets for the most November to February sunlight. Choose a site on the southwest or west side as the next-best choice. Avoid placing the greenhouse next to trees that might block the sun in the morning.
Sometimes greenhouses get added to a house or garage while others work as freestanding buildings. Lean-to greenhouses, some of the least expensive structures, lean against the length of another building. Even-span greenhouses tend to cost the most but they also provide the most space. The short wall of the even-span greenhouse leans into another building with the length of the greenhouse stretching away from the building. Freestanding greenhouses, on the other hand, stand apart from other buildings and tend to get more sun.
Greenhouses are constructed from wood, galvanized steel, metal pipes or aluminum. Coverings for the frames includes glass, rigid fiberglass or plastic film. Fiberglass works well in areas that get hail. Double-wall plastic sheets of acrylic or polycarbonate provide heat-saving covers with two layers of rigid plastic. For lightweight structures, low-cost plastic film may work best although it requires replacing more often. Flooring should consist of a gravel, concrete or stone walkway 24 to 36 inches wide that allows people to easily access the plants. Water sprayed on the gravel also provides humidity for the greenhouse.
While the sun provides some sunlight and heat for a greenhouse, it needs a regulated system. Factors to consider include the desired temperature for the plants, the location and construction of the structure, and the total exposed area of the greenhouse. Heating sources including electricity, gas or wood distributed by forced hot air, radiant heat, hot water or steam.
Circulation and Ventilation
Since warm air rises to the top of the structure and cool air settles around the floor, air circulation helps to keep temperatures even in all areas of the greenhouse. Small fans running all winter provide ventilation, as does the fan in a forced-air heating system. Greenhouses also need ventilation to exchange inside air with outside air while helping control temperatures, remove humidity and replenish carbon dioxide. Consider using roof vents or mechanical ventilation with exhaust fans to handle the job.