There are two general categories of greenhouse parts. Structural parts such as framing, wall covering, and seals form the building itself. Other parts such as heaters, irrigation, ventilation systems, and growing accessories are used to maintain an optimal growing environment inside the greenhouse. Specific parts vary depending on the size and permanence of the structure, the climate the greenhouse will be in, and the weather conditions the greenhouse will likely face.
Greenhouses are traditionally made of glass. Glass is easy to maintain, lasts a long time, has a clean appearance, and allows a lot of light to penetrate through to the plants inside. A glass structure is fairly weather proof and preserves heat and humidity levels inside if properly sealed. On the downside, glass is easily broken and requires a heavier, more substantial frame and foundation to support its weight. The initial cost of the glass and the necessary support structure make glass the most expensive type of greenhouse covering.
Fiberglass is also used for covering greenhouses. It is lightweight, strong, and is virtually unbreakable. Fiberglass is clear, allowing for light penetration, and can be made fairly weatherproof with tight seals. The disadvantage to fiberglass is that it degrades in about 10 to 15 years, and the amount of light penetration decreases over time.
Double-walled plastic coverings for greenhouses are rigid sheets of double-layered plastic with webbing in the middle. This type of covering has the advantage of light penetration nearly equal to glass, but provides better insulation. Heat retention is particularly important in cold climates, and can reduce heating costs.
Plastic sheets and film plastic are lightweight, inexpensive, and are available in different qualities. They do not require a permanent, substantial frame or foundation and are quick and easy to install. These cheaper options allow for decent light penetration, minimal insulation, and are not meant to last for more than a few years.
Greenhouse framing largely depends on the intended permanence of the structure, the type of wall covering it will support, and the environmental elements it will face such as strong wind, heavy snow, or hail. Traditional glass greenhouses are supported by steel, aluminum, or wooden frames. Cheaper, less permanent greenhouses can be made of plastic PVC pipes, metal pipes, or thin wooden frames. The wall covering is typically fastened to the frame with nuts and bolts.
Depending on the climate and season, it may be necessary to regulate the temperature and humidity levels within the greenhouse. An electric, gas, oil or solar heater can keep plants warm and growing throughout the winter. In warmer climates, gardeners might need to cool their greenhouses with fans, evaporative coolers, or shade cloth. Air can also be ventilated with fans, vents, and exhaust systems.
Once the greenhouse is constructed, there are many accessories that make greenhouse gardening easier. Shelving, growing lights, flooring, thermometers, seed trays, potting trays, and hand gardening tools are all common items in a greenhouse. Popular types of irrigation include hoses, watering cans, mist sprayers, foggers, humidifiers, sprinklers, and automatic drip hoses.
Greenhouse parts are readily available at most home improvement stores. Specialty stores and Internet retailers also sell greenhouse parts. Some gardeners find it convenient to order a pre-assembled kit containing all of the necessary greenhouse parts directly from a greenhouse manufacturer.