Greenhouse gardening helps create a controlled environment in which to grow garden plants. Greenhouses help extend the vegetable gardening season, and are useful for protecting your vegetables during the less predictable spring and fall weather. In some cases, greenhouses can re-create a plant's native environment entirely. A greenhouse can also be a place of calm and rest, used for entertaining guests, or just reading a book in a quiet, warm, and tropical environment.
How Greenhouse Gardening Works
Greenhouses are structural buildings that operate by capturing more energy than they release - greenhouses trap heat.
The walls and roof of a greenhouse are often made of glass and/or plastic. These materials allow solar radiation from the sun to pass through from the exterior. The solar radiation is absorbed by the vegetable plants, soil, and surfaces within the greenhouse. The air within the greenhouse is warmed by these hot interior surfaces and is trapped inside by the walls and roof.
Ventilation is a necessary part of greenhouse gardening due to the fact that without ventilation, overheating can occur. Greenhouses usually have at least two vents to facilitate ventilation; one located on or near the top of the roof that lets rising, warm air out, and; another vent located somewhere on the lower half of the structure that lets cooler air in.
Proper ventilation will prevent the inside air from overheating and becoming stale and it also helps recycle the carbon dioxide needed for photosynthesis. Greenhouse blinds can be used to provide shade and keep your greenhouse from over-heating your plants.
Greenhouse Irrigation - Closed Loop vs. Open Loop
Water is required near your greenhouse location. Hand watering is time-consuming, and so automated systems such as booms, sprinklers, wicking, capillary matting, or drip irrigation is often used. Watering systems are usually grouped into one of two categories: closed systems or open systems. Closed systems use recirculated nutrient solutions for feeding vegetables. In a closed system, the solution can reach the roots, but never leach out into the outside environment or external soil.
Closed loop irrigation systems allow control of the water flow that reaches your vegetable garden. Open irrigation systems are the opposite, allowing the nutrient solution to filter through the roots and out into the external environment. Open loops systems produce a continuous flow, are usually only turned on or off, and do not adjust themselves according to external stimuli.
Greenhouses in colder climates requires artificial heating in order to keep the vegetable plants from freezing. Methods of heating include furnaces, boilers, heating fans, and heating coils, and solar heating systems.
Types of Greenhouses Used for Greenhouse Gardening
Most structures used for greenhouse gardening are either build as a lean-to or freestanding structure. A Lean-to is a form of greenhouse is built on the side of a larger structure, sharing a common wall for support. Lean-to greenhouses can be among the least inexpensive to build.
The location of the lean-to is a very important consideration, ensuring that it will not be shaded by the structure it is built against. Freestanding greenhouses are stand-alone structures that require their own heating and watering system. Freestanding greenhouses can be positioned in location to allow the maximum amount of light from all sides.
The Various Functions of Greenhouses
Cold-Frame - a small lean-to or freestanding greenhouse that has no source of heat. It is primarily used in spring when hardening off vegetable plants before transplanting into the garden. Cold-frames can vary in size.
Residential - this type of greenhouse is used primarily for personal use, and is often a DIY (do-it-yourself). Small greenhouse kits are an excellent way to quickly and easily build a greenhouse in your backyard. The size and complexity of a residential greenhouse will depend on your available space and budget.
Commercial - commercial greenhouses allow large-scale production of vegetables. They have grown steadily in use since World War 2, and usually employ fully automated heating and watering systems.
Conservatory - conservatories are designed to showcase garden plants. Conservatories can be of a residential or commercial nature, but commonly have ornate floors, furnishings and decor.