Greenhouses are a fun way to grow plants indoors for the dedicated hobbyist. They are also an important tool for the commercial flower industry, serving as a source of plants that would otherwise not be available in winter months. Greenhouses have been around for centuries and today use high-tech materials and designs. While there are several different types of greenhouses, all rely on the same basic scientific principles to create an environment where plants can flourish.
How Do They Work?
Greenhouses work by using the basic scientific principle that incoming heat from the sun can be trapped and used to warm an interior space. Greenhouses use a transparent roof and walls to allow heat and light from the sun to enter. The heat then reflects inside the greenhouse and is trapped, where it causes the space to warm up. At night, when the sun sets and the outdoor temperature drops, the air inside the greenhouse still contains the energy captured from the sun during the day. Before it can get too cool inside the greenhouse, the sun rises again the the process starts over.
What Materials Are Used?
Most greenhouses use glass standard panes or transparent plastic sheeting for their walls and roofs. The material of choice depends on how much heat is needed inside the greenhouse, and how much sunshine typically occurs in the region where the greenhouse is constructed. The greenhouse walls are attached to a rigid metal frame. In some cases the frame is attached to another building, such as a house orlaboratory, but other greenhouses use a free-standing frame. Most greenhouses also include rocks or water to absorb heat from the sun during the day and release it slowly at night, keeping the temperature warm.
What Can They Grow?
People have used greenhouses to grow many varieties of fruits and vegetables as well as flowers and other plants. The idea behind a greenhouse is to imitate the natural climate of the region where a plant grows well. According to the Greenhouse Gardener's Companion, some popular greenhouse plants include tomatoes, sweet peas, herbs and leafy greens.
What Else Is Needed?
Besides transparent panels for collecting heat from the sun, most greenhouses also feature a fan for ventilation. These fans allow gardeners to draw in air from outside or to vent air from inside the greenhouse, thus warming or cooling the space as necessary. A greenhouse operator may also install a humidifier to add moisture to the air, creating a warm, humid environment that certain plants thrive in. The plants inside also need regular watering and the sun's heat to grow. Beyond these basics many greenhouses also use special pots, soils and fertilizers to keep the plants healthy.
Where Should They Be Built?
Greenhouses are most useful in regions where temperatures drop during the winter months to levels that would make it impossible to grow certain plants. However, they are useful anywhere that gardeners desire a constant, controllable indoor climate. Greenhouses should be built in an open space where they receive as much direct sunlight as possible without nearby buildings or trees casting shadows on their roofs. Greenhouse Gardener's Companion suggests that greenhouses in the northern hemisphere be situated so that they face within 20 degrees of true south for maximum sun exposure.