The basic concept of a greenhouse is to take optimal advantage of sunlight and its warmth to grow plants. A greenhouse should be located to take full advantage of sunlight and minimize the shade of trees or nearby buildings, especially in winter. Some shadows in the summer might help keep the inside temperature of a greenhouse within a healthy range for the plants. Deciduous trees can be an advantage, if the site is not heavily forested, because when they shed their leaves in the fall, the greenhouse will have the full benefit of winter sun. The goal of most greenhouses is to protect plants from winter cold, and to capture as much light as possible during shorter winter days. To achieve a balance between the different seasons, some additional shading and cooling is commonly needed during the summer. An additional source of heat, and perhaps supplementary lighting, might also be necessary in winter, depending on the existing climate.
In the Northern Hemisphere, primary greenhouse orientation (the long side of the structure) should be toward the south whenever possible. The north-facing side of a greenhouse typically will be the area for locating necessary equipment, a storage shed or solid wall, and should be the most protected side. If southern exposure is not possible, try to locate the long dimension of the greenhouse toward the southeast rather than southwest or directly west. Morning sun and warmth will help warm the greenhouse, but summer sun can make a greenhouse interior unbearably hot in the afternoon, even in northern states with moderate climates. The value of a properly-oriented solar greenhouse is that the warmth and light provided by the sun will maximize the growing season as efficiently and naturally as possible. The addition of supplementary heating and cooling will, of course entail additional costs both for installation and for operation.
