A polytunnel is a structure made of polyethylene which is designed to protect a row of plants or a section of a garden. Polytunnels come in all shapes and sizes, from small models designed for home gardeners to much larger tunnels which are meant for commercial use. It is possible to order a polytunnel, usually in kit form, from a manufacturer which specializes in garden supplies, and thrifty gardeners can also build their own, as long as they have access to framing materials and a source of polyethylene.
For gardeners, a polytunnel straddles the dividing line between greenhouses and cloches. A cloche is a small plastic structure which is usually designed to protect a single plant from the elements. Cloches usually use a simple metal or wooden framework which can be draped with plastic and moved as needed. They protect young plants while they grow, and they can also be used to minimize frost and pest damage. A greenhouse is a much larger structure which houses an entire indoor garden. Greenhouses can be made from glass or plastic, and they are designed to give a gardener greater control over temperature and humidity.
Unlike most greenhouses, a polytunnel can usually be easily moved around, and it is much cheaper to build. However, a polytunnel serves much the same function. It protects plants from severe weather, and it can be used to increase heat and humidity for plants which favor these conditions. By using a polytunnel, a gardener can grow plants which will not normally thrive where he or she lives.
There are some other advantages to polytunnels. Since many can be completely sealed, they also protect plants from insect infestations, which can devastate a crop. A sturdy polytunnel will also repel larger pests such as deer and birds. It is also possible to build raised and sealed beds in a polytunnel, using fresh soil. This can be useful for gardeners who have less than ideal soil to work with, and it can retard soil-borne pests which might otherwise be an issue.
These distinctive polyethylene tunnels can be seen in gardens and commercial farming operations in many parts of the world. Although a polytunnel may not be terribly impressive or pleasant to look at, it serves a useful function, allowing people to produce a range of plants for decoration and consumption. Generally, they are used in temperate zones, with gardeners in cold regions using hothouses to grow their plants.