Polytunnel

A polytunnel (also known as a polyhouse, hoop greenhouse or hoophouse, or high tunnel) is a tunnel made of polyethylene, usually semi-circular, square or elongated in shape. The interior heats up because incoming solar radiation from the sun warms plants, soil, and other things inside the building faster than heat can escape the structure. Air warmed by the heat from hot interior surfaces is retained in the building by the roof and wall. Temperature, humidity and ventilation can be controlled by equipment fixed in the polytunnel

Polytunnels on Balhungie Farm, Angus

Uses

Polytunnels can be used to provide a higher temperature and/or humidity than that which is available in the environment but can also protect crops from intense heat, bright sunlight, strong winds, hailstones and cold waves. This allows fruits and vegetables to be grown at times usually considered off season. Every factor influencing a crop can be controlled in a polytunnel. Polytunnels are often used in floriculture and nurseries as the economic value of flowers can justify their expense.

Temperate regions

Polytunnels are mainly used in temperate regions in similar ways to greenhouses and cloches (row covers). Modern designs allow sowing and harvesting machines to move inside the structures so as to automate production. Polytunnels have had a significant effect on the production of strawberries in the United Kingdom. Other soft fruits such as raspberries and blackberries are also cultivated in the same way.

Other regions

A Missouri farmer inspecting an early tomato crop in a hoop house.

In a tropical climate, temperatures are prone to soar above all normal levels. In such cases, foggers/misters are used to reduce the temperature. This does not enhance the humidity levels in the poly house as the evaporated droplets are almost immediately ventilated to open air.
High tech poly houses even have heating systems as well as soil heating systems to purify the soil of unwanted viruses, bacteria etc.The recent Indo-Israel collaboration at Gharunda, near Karnal is an excellent example of Polyhouse farming taking place in a developing country. If the developing countries try and develop a special program only for the farmers especially in countries like India the migration rate of the rural population to urban areas and the migration of farmers from agri/horticulture to urban areas may be reduced.This has a huge potential to improve the farming sector which has so far proved to be the vitally important sector for any country to stabilise the economy. The projects with small polytunnels used by each farmer in each village promoting cultivation of vegetables for on season and off season would actually help to develop the practise of moderating the market rate for the vegetable in long run round the year and would eventually help cultivate at least for the needsof the nearest market thus stabilising the market rate. In India, the inability to grow tomato during rainy season allows its price to soar during the monsoon. This is spotted as an ideal time to grow tomato in polytunnels providing the ideal climate for the crop. In India, Abhinav Farmers Club grows flowers and organic vegetables in polytunnels.