How Does a Greenhouse Work

Gardenerdy Staff Nov 25, 2018
A greenhouse creates and maintains the perfect conditions for plants to flourish in. This is not only explanation of the working process of a greenhouse, but also examines other aspects of these structures. Read next...
Fast Fact
Netherlands has the largest number of greenhouses in the world, with about 9000 companies investing in building these structures. Crop production due to these structures amounts to a revenue of around 7.2 billion pounds in this country.
A greenhouse is a large structure, with walls and roof often built entirely of glass or plastic. It is a house for plants, filled with equipment like screening installations, heating, cooling, lighting, etc., that helps to maintain controlled environment for plants.
Greenhouses are used for growing all kinds of plants, including flowers, fruits, and vegetables. These structures are often used to grow saplings in the late winter and early spring, which are later planted in the open in warmer weather.
Pollination of the plants is done naturally by bees, or artificial pollination may be done, as per the need. Greenhouses protect plants from weather phenomena like blizzards or dust storms.
Have you ever wondered how do greenhouses work? The widely spread (and believed) explanation is based on the varying transparency of glass to solar and thermal infrared radiation. This misconception explains that solar radiation enters the greenhouse through the glass, and heats up the interior, which is true.
It then says that all the heated surfaces emit longer wavelengths that are unable to pass through the glass, and hence, this radiation stays within the greenhouse. Consequently, this is how the greenhouse retains heat.
However, if this were true, why would polyethylene greenhouses also retain heat, for polyethylene is almost as transparent to thermal infrared radiation, as it is to solar radiation.

How Greenhouses Works

The correct explanation is that working starts with the heat carrying rays of the sun entering the walls and/or roof of greenhouse, heating up the interiors.
Plants grow well in humid, temperate heated environment, and good water source. The sun's rays are in form of short range infrared waves, which converted to long range infrared waves. The temperature of the ground rises as it absorbs this radiation. The heat is also absorbed by the plants, which helps in the process of photosynthesis.
The heat from the ground is transmitted to the layer of air next to it, which expands and becomes lighter than the air above it. This air rises, and gets replaced by cooler denser air. This convection cycle continues throughout the day. The roof and walls of the greenhouse retain this heated air, and so, the air in the greenhouse stays warm all day long.
In an open space, the heating of air is spread over a large mass, and is diluted. In the nights, the temperature in a greenhouse stays warmer than the air outside, as heat stored during the day is available throughout the night.
Many conditions need to be monitored and maintained, in order to grow and sustain different types of plants in a greenhouse. It must have a good ventilation system, to avoid overheating. The plants need to be watered, and periodically checked for pests or disease.
Special care may be needed in winters, to preserve plant health, especially for warm-weathered plants. One may need to arrange additional heat and light.
It allows cultivation and production of plants, not naturally growing during winters. They can also ensure a yearly supply of staple vegetables like lettuce.
In addition to this, greenhouses play a very important role in providing a constant food supply to countries at high latitudes. The greenhouse complexes in Almeria, Spain are one such example. They are among the largest of its kind in the world, covering almost 50,000 acres of land.