![Polytunnel Balhungie](https://upload.wikimedia.org/wikipedia/commons/b/b0/Polytunnel_Balhungie.jpg)
A polytunnel (also known as a polyhouse, hoop greenhouse or hoophouse, grow tunnel or high tunnel) is a tunnel typically made from steel and covered in
polyethylene
Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including bo ...
, usually semi-circular, square or elongated in shape. The interior heats up because incoming
solar radiation
Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre (W/m ...
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
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
,
humidity
Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present.
Humidity depe ...
and
ventilation
Ventilation may refer to:
* Ventilation (physiology), the movement of air between the environment and the lungs via inhalation and exhalation
** Mechanical ventilation, in medicine, using artificial methods to assist breathing
*** Ventilator, a m ...
can be controlled by equipment fixed in the polytunnel or by manual opening and closing of vents. Polytunnels are mainly used in temperate regions in similar ways to glass
greenhouse
A greenhouse (also called a glasshouse, or, if with sufficient heating, a hothouse) is a structure with walls and roof made chiefly of Transparent ceramics, transparent material, such as glass, in which plants requiring regulated climatic condit ...
s and
row cover
In agriculture and gardening, row cover is any transparent or semi-transparent flexible material, like fabric or plastic sheeting, used as a protective covering for plants, usually vegetables. Covers are used to extend growing seasons, and redu ...
s. Besides the
passive solar
In passive solar building design, windows, walls, and floors are made to collect, store, reflect, and distribute solar energy, in the form of heat in the winter and reject solar heat in the summer. This is called passive solar design because, unli ...
heating that every polytunnel provides, every variation of auxiliary heating (from hothouse heating through minimal heating to unheated houses) is represented in current practice. The nesting of row covers and low tunnels inside high tunnels is also common.
![Superbay Polytunnel](https://upload.wikimedia.org/wikipedia/commons/6/69/Superbay_Polytunnel.jpg)
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,
wind
Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hou ...
s,
hail
Hail is a form of solid precipitation. It is distinct from ice pellets (American English "sleet"), though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailstone. Ice pellets generally fal ...
stones, and
cold wave
A cold wave (known in some regions as a cold snap, cold spell or Arctic Snap) is a weather phenomenon that is distinguished by a cooling of the air. Specifically, as used by the U.S. National Weather Service, a cold wave is a rapid fall in tem ...
s. This allows
fruit
In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering.
Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particu ...
s and
vegetable
Vegetables are parts of plants that are consumed by humans or other animals as food. The original meaning is still commonly used and is applied to plants collectively to refer to all edible plant matter, including the flowers, fruits, stems, ...
s to be grown at times usually considered off season;
market garden
A market garden is the relatively small-scale production of fruits, vegetables and flowers as cash crops, frequently sold directly to consumer
A consumer is a person or a group who intends to order, or uses purchased goods, products, or s ...
ers commonly use polytunnels for
season extension
Season extension in agriculture is any method that allows a crop to be grown beyond its normal outdoor growing season and harvesting time frame, or the extra time thus achieved. To extend the growing season into the colder months, one can use un ...
. Beyond season extension, polytunnels are also used to allow cold-hardy crops to
overwinter
Overwintering is the process by which some organisms pass through or wait out the winter season, or pass through that period of the year when "winter" conditions (cold or sub-zero temperatures, ice, snow, limited food supplies) make normal activi ...
in regions where their
hardiness is not quite strong enough for them to survive outdoors. Temperature increases of only above outdoor ambient, coupled with protection from the
drying
Drying is a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid. This process is often used as a final production step before selling or packaging products. To be considered ...
effect of
wind
Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hou ...
, are enough to let selected plant varieties grow slowly but healthily instead of dying. The effect is to create a
microclimate
A microclimate (or micro-climate) is a local set of atmospheric conditions that differ from those in the surrounding areas, often with a slight difference but sometimes with a substantial one. The term may refer to areas as small as a few squ ...
that simulates the temperatures of a location several hardiness zones closer to the equator (and protects from wind as well).
![Bespoke Superbay Polytunnel](https://upload.wikimedia.org/wikipedia/commons/8/8f/Bespoke_Superbay_Polytunnel.jpg)
Every factor influencing a crop can be controlled in a polytunnel. Polytunnels are often used in
floriculture
Floriculture, or flower farming, is a branch of horticulture concerned with the cultivation of flowering and ornamental plants for gardens and for floristry, comprising the floral industry. The development of new varieties by plant breeding is ...
and
plant nurseries
A nursery is a place where plants are propagated and grown to a desired size. Mostly the plants concerned are for gardening, forestry or conservation biology, rather than agriculture. They include retail nurseries, which sell to the general p ...
, as the
revenue
In accounting, revenue is the total amount of income generated by the sale of goods and services related to the primary operations of the business.
Commercial revenue may also be referred to as sales or as turnover. Some companies receive reven ...
value of the plants can justify the expense.
In recent years the true adaptability of polytunnel structures has been realised by adapting them to suit livestock housing. It is now commonplace in the UK to see polytunnels used for housing
sheep
Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus ''Ovis'', in everyday usage it almost always refers to domesticated s ...
,
alpacas
The alpaca (''Lama pacos'') is a species of South American camelid mammal. It is similar to, and often confused with, the llama. However, alpacas are often noticeably smaller than llamas. The two animals are closely related and can successf ...
,
goats
The goat or domestic goat (''Capra hircus'') is a domesticated species of Caprinae, goat-antelope typically kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a membe ...
,
calves and
poultry
Poultry () are domesticated birds kept by humans for their eggs, their meat or their feathers. These birds are most typically members of the superorder Galloanserae (fowl), especially the order Galliformes (which includes chickens, quails, a ...
.
Climatic differences
Temperate regions
Polytunnels are mainly used in temperate regions in similar ways to
greenhouse
A greenhouse (also called a glasshouse, or, if with sufficient heating, a hothouse) is a structure with walls and roof made chiefly of Transparent ceramics, transparent material, such as glass, in which plants requiring regulated climatic condit ...
s and cloches (
row cover
In agriculture and gardening, row cover is any transparent or semi-transparent flexible material, like fabric or plastic sheeting, used as a protective covering for plants, usually vegetables. Covers are used to extend growing seasons, and redu ...
s). 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
The garden strawberry (or simply strawberry; ''Fragaria × ananassa'') is a widely grown hybrid species of the genus '' Fragaria'', collectively known as the strawberries, which are cultivated worldwide for their fruit. The fruit is widely ap ...
in the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
. Other soft fruits such as
raspberries
The raspberry is the edible fruit of a multitude of plant species in the genus ''Rubus'' of the rose family, most of which are in the subgenus '' Idaeobatus''. The name also applies to these plants themselves. Raspberries are perennial with w ...
and
blackberries
The blackberry is an edible fruit produced by many species in the genus ''Rubus'' in the family (biology), family Rosaceae, hybrids among these species within the subgenus ''Rubus'', and hybrids between the subgenera ''Rubus'' and ''Idaeobatus' ...
are also cultivated in the same way.
Other regions
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 increase the humidity levels in the poly house as the evaporated droplets are almost immediately ventilated to open air.
High-tech poly houses even have space-heating systems as well as soil-heating systems to purify the soil of unwanted viruses, bacteria, and other organisms. The recent Indo-Israel collaboration at Gharunda, near
Karnal
Karnal ( is a city located in the state of Haryana, India and is the administrative headquarters of Karnal District. It was used by East India Company army as a refuge during the Indian Rebellion of 1857 in Delhi. The Battle of Karnal between ...
is an excellent example of Polyhouse farming taking place in a developing country.
![Solar Single Span Hobby Polytunnel](https://upload.wikimedia.org/wikipedia/commons/c/c3/Solar_Single_Span_Hobby_Polytunnel.jpg)
If developing countries were to develop a special incentive program solely for fruit-and-vegetable farmers, especially in demographically large nations like India, then the migration rate from rural to urban areas (as well as the loss of horticultural and fruit/vegetable farmers) to urban areas may be reduced. This brings a huge potential to improve the farming sector, which is key to long-term economic stability. The small polytunnels used by each farmer in each village promote the cultivation of vegetables both on-season and off-season, and would actually help to moderate the market rate for fruit and vegetables in long run, on a year-round basis, and would help to satisfy local market needs.
For example, in India, the inability to grow tomatoes generates price spikes during the monsoon season. This is seen as an ideal time to grow tomatoes in polytunnels, since they provide the ideal climate for the crop. In India, the
Abhinav Farmers Club grows flowers and organic vegetables in polytunnels.
Development
![Hoop house](https://upload.wikimedia.org/wikipedia/commons/2/22/Hoop_house.jpg)
Hoophouses have existed at least since the 1940s, but they are much more commonly used with each passing decade, and their design continues to evolve. Because of the wide variety of constantly changing designs, in reality there is an entirely
continuous
Continuity or continuous may refer to:
Mathematics
* Continuity (mathematics), the opposing concept to discreteness; common examples include
** Continuous probability distribution or random variable in probability and statistics
** Continuous ...
spectrum from high tunnels through low tunnels to the simplest row covers, although they are often thought about as discrete steps. Major themes of continuing development are (1) achieving the same results with lighter construction and less cost and (2) making hoophouses easily movable. The advantages of mobile hoophouses include greater
return on investment
Return on investment (ROI) or return on costs (ROC) is a ratio between net income (over a period) and investment (costs resulting from an investment of some resources at a point in time). A high ROI means the investment's gains compare favourably ...
(with the same unit of investment getting greater use per year across different crops in different months) and more flexibility on
crop rotation
Crop rotation is the practice of growing a series of different types of crops in the same area across a sequence of growing seasons. It reduces reliance on one set of nutrients, pest and weed pressure, and the probability of developing resistant ...
without ever having to bother to dig the soil out of a stationary house (or use
soil steam sterilization
Soil steam sterilization (soil steaming) is a farming technique that sterilizes soil with steam in open fields or greenhouses. Pests of plant cultures such as weeds, bacteria, fungi and viruses are killed through induced hot steam which cause ...
) to cure greenhouse soil sickness.
A
US Department of Agriculture
The United States Department of Agriculture (USDA) is the United States federal executive departments, federal executive department responsible for developing and executing federal laws related to farming, forestry, rural economic development, ...
program is helping farmers install polytunnels. The program was announced at the US
White House
The White House is the official residence and workplace of the president of the United States. It is located at 1600 Pennsylvania Avenue NW in Washington, D.C., and has been the residence of every U.S. president since John Adams in 1800. ...
garden in December 2009.
Farmers in
Iraq
Iraq,; ku, عێراق, translit=Êraq officially the Republic of Iraq, '; ku, کۆماری عێراق, translit=Komarî Êraq is a country in Western Asia. It is bordered by Turkey to Iraq–Turkey border, the north, Iran to Iran–Iraq ...
are building these in increasing number and adding
drip irrigation
Drip irrigation or trickle irrigation is a type of micro-irrigation system that has the potential to save water and nutrients by allowing water to drip slowly to the roots of plants, either from above the soil surface or buried below the surface. ...
to grow tomatoes.
References
External links
*. 11 December 2009 by {{YouTube, user= usda , title= USDA , link= no.
Polytunnelson Hortweek 1 November 2016
Polytunnels: Second generationon Hortweek 13 February 2015
Polytunnels - Fresh Produceon Hortweek 6 November 2015
Agricultural buildings
Greenhouses
Horticulture
Portable buildings and shelters