A greenhouse (also called a glasshouse, or, if with sufficient heating, a hothouse) is a structure with walls and roof made chiefly of transparent material, such as glass, in which plants requiring regulated climatic conditions are grown. These structures range in size from small sheds to industrial-sized buildings. A miniature greenhouse is known as a cold frame. The interior of a greenhouse exposed to sunlight becomes significantly warmer than the external ambient temperature, protecting its contents in cold weather.
Many commercial glass greenhouses or hothouses are high tech production facilities for vegetables or flowers. The glass greenhouses are filled with equipment including screening installations, heating, cooling, lighting, and may be controlled by a computer to optimize conditions for plant growth. Different techniques are then used to evaluate optimality-degrees  and comfort ratio of greenhouse micro-climate (i.e., air temperature, relative humidity and vapor pressure deficit) in order to reduce production risk prior to cultivation of a specific crop.
The idea of growing plants in environmentally controlled areas has existed since Roman times. The Roman emperor Tiberius ate a cucumber-like vegetable daily. The Roman gardeners used artificial methods (similar to the greenhouse system) of growing to have it available for his table every day of the year. Cucumbers were planted in wheeled carts which were put in the sun daily, then taken inside to keep them warm at night. The cucumbers were stored under frames or in cucumber houses glazed with either oiled cloth known as specularia or with sheets of selenite (a.k.a. lapis specularis), according to the description by Pliny the Elder.
Greenhouses in which the temperature could be manually manipulated first appeared in 15th century Korea. The 15th century treatise, the Sanga Yorok, contains descriptions of greenhouses designed to regulate the temperature and humidity requirements of plants and crops. One of the earliest records of the Annals of the Joseon Dynasty in 1438 confirms growing mandarin orange trees in a traditional Korean greenhouse during the winter and installing an ondol system to provide heat.
The concept of greenhouses also appeared in the Netherlands and then England in the 17th century, along with the plants. Some of these early attempts required enormous amounts of work to close up at night or to winterize. There were serious problems with providing adequate and balanced heat in these early greenhouses. Today, the Netherlands has many of the largest greenhouses in the world, some of them so vast that they are able to produce millions of vegetables every year.
The French botanist Charles Lucien Bonaparte is often credited with building the first practical modern greenhouse in Leiden, Holland, during the 1800s to grow medicinal tropical plants. Originally only on the estates of the rich, the growth of the science of botany caused greenhouses to spread to the universities. The French called their first greenhouses orangeries, since they were used to protect orange trees from freezing. As pineapples became popular, pineries, or pineapple pits, were built.
Experimentation with the design of greenhouses continued during the 17th century in Europe, as technology produced better glass and construction techniques improved. The greenhouse at the Palace of Versailles was an example of their size and elaborateness; it was more than 150 metres (490 ft) long, 13 metres (43 ft) wide, and 14 metres (46 ft) high.
The golden era of the greenhouse was in England during the Victorian era, where the largest glasshouses yet conceived were constructed, as the wealthy upper class and aspiring botanists competed to build the most elaborate buildings. A good example of this trend is the pioneering Kew Gardens. Joseph Paxton, who had experimented with glass and iron in the creation of large greenhouses as the head gardener at Chatsworth, in Derbyshire, working for the Duke of Devonshire, designed and built The Crystal Palace in London, (although the latter was constructed for both horticultural and non-horticultural exhibition).
In the 20th century, the geodesic dome was added to the many types of greenhouses. Notable examples are the Eden Project, in Cornwall, The Rodale Institute in Pennsylvania, the Climatron at the Missouri Botanical Garden in St. Louis, Missouri, and Toyota Motor Manufacturing Kentucky.
Greenhouse structures adapted in the 1960s when wider sheets of polyethylene film became widely available. Hoop houses were made by several companies and were also frequently made by the growers themselves. Constructed of aluminum extrusions, special galvanized steel tubing, or even just lengths of steel or PVC water pipe, construction costs were greatly reduced. This resulted in many more greenhouses being constructed on smaller farms and garden centers. Polyethylene film durability increased greatly when more effective UV-inhibitors were developed and added in the 1970s; these extended the usable life of the film from one or two years up to 3 and eventually 4 or more years.
Gutter-connected greenhouses became more prevalent in the 1980s and 1990s. These greenhouses have two or more bays connected by a common wall, or row of support posts. Heating inputs were reduced as the ratio of floor area to exterior wall area was increased substantially. Gutter-connected greenhouses are now commonly used both in production and in situations where plants are grown and sold to the public as well. Gutter-connected greenhouses are commonly covered with structured polycarbonate materials, or a double layer of polyethylene film with air blown between to provide increased heating efficiencies.
The explanation given in most sources for the warmer temperature in a greenhouse is that incident solar radiation (the visible and adjacent portions of the infrared and ultraviolet ranges of the spectrum) passes through the glass roof and walls and is absorbed by the floor, earth, and contents, which become warmer and re-emit the energy as longer-wavelength infrared radiation. Glass and other materials used for greenhouse walls do not transmit infrared radiation, so the infrared cannot escape via radiative transfer. As the structure is not open to the atmosphere, heat also cannot escape via convection, so the temperature inside the greenhouse rises. This is known as the "greenhouse effect". The greenhouse effect, due to infrared-opaque "greenhouse gases", including carbon dioxide and methane instead of glass, also affects the earth as a whole; there is no convective cooling as air does not escape from the earth.
However, R. W. Wood in 1909 constructed two greenhouses, one with glass as the transparent material, and the other with panes of rock salt, which is transparent to infrared. The two greenhouses warmed to similar temperatures, suggesting that an actual greenhouse is warmer not because of the "greenhouse effect", but by preventing convective cooling, not allowing warmed air to escape.
More recent quantitative studies suggest that the effect of infrared radiative cooling is not negligibly small, and may have economic implications in a heated greenhouse. Analysis of issues of near-infrared radiation in a greenhouse with screens of a high coefficient of reflection concluded that installation of such screens reduced heat demand by about 8%, and application of dyes to transparent surfaces was suggested. Composite less-reflective glass, or less effective but cheaper anti-reflective coated simple glass, also produced savings.
Ventilation is one of the most important components in a successful greenhouse, specially in hot and humid tropical climate condition. If there is no proper ventilation, greenhouses and their growing plants can become prone to problems. The main purposes of ventilation are to regulate the temperature, humidity and vapor pressure deficit  to the optimal level, and to ensure movement of air and thus prevent build-up of plant pathogens (such as Botrytis cinerea) that prefer still air conditions. Ventilation also ensures a supply of fresh air for photosynthesis and plant respiration, and may enable important pollinators to access the greenhouse crop.
Ventilation can be achieved via use of vents - often controlled automatically via a computer - and recirculation fans.
Heating or electricity is one of the most considerable costs in the operation of greenhouses across the globe, especially in colder climates. The main problem with heating a greenhouse as opposed to a building that has solid opaque walls is the amount of heat lost through the greenhouse covering. Since the coverings need to allow light to filter into the structure, they conversely cannot insulate very well. With traditional plastic greenhouse coverings having an R-value of around 2, a great amount of money is therefore spent to continually replace the heat lost. Most greenhouses, when supplemental heat is needed use natural gas or electric furnaces.
Passive heating methods exist which seek heat using low energy input. Solar energy can be captured from periods of relative abundance (day time/summer), and released to boost the temperature during cooler periods (night time/winter). Waste heat from livestock can also be used to heat greenhouses, e.g., placing a chicken coop inside a greenhouse recovers the heat generated by the chickens, which would otherwise be wasted.
Electronic controllers are often used to monitor the temperature and adjusts the furnace operation to the conditions. This can be as simple as a basic thermostat, but can be more complicated in larger greenhouse operations.
Carbon dioxide enrichment
The possibility of using carbon dioxide enrichment in greenhouse cultivation to enhance plant growth has been known for nearly 100 years. After the development of equipment for the controlled serial enrichment of carbon dioxide, the technique was established on a broad scale in the Netherlands. Secondary metabolites, e.g., cardiac glycosides in Digitalis lanata, are produced in higher amounts by greenhouse cultivation at enhanced temperature and at enhanced carbon dioxide concentration. Commercial greenhouses are now frequently located near appropriate industrial facilities for mutual benefit. For example, Cornerways Nursery in the UK is strategically placed near a major sugar refinery, consuming both waste heat and CO2 from the refinery which would otherwise be vented to atmosphere. The refinery reduces its carbon emissions, whilst the nursery enjoys boosted tomato yields and does not need to provide its own greenhouse heating.
Enrichment only becomes effective where, by Liebig's law, carbon dioxide has become the limiting factor. In a controlled greenhouse, irrigation may be trivial, and soils may be fertile by default. In less-controlled gardens and open fields, rising CO2 levels only increase primary production to the point of soil depletion (assuming no droughts, flooding, or both), as demonstrated prima facie by CO2 levels continuing to rise. In addition, laboratory experiments, free air carbon enrichment (FACE) test plots, and field measurements provide replicability.
In domestic greenhouses, the glass used is typically 3mm (or ⅛″) 'horticultural glass' grade, which is good quality glass that should not contain air bubbles (which can produce scorching on leaves by acting like lenses).
Commercial glass greenhouses are often high-tech production facilities for vegetables or flowers. The glass greenhouses are filled with equipment such as screening installations, heating, cooling and lighting, and may be automatically controlled by a computer.
In the UK and other Northern European countries a pane of horticultural glass referred to as "Dutch Light" was historically used as a standard unit of construction, having dimensions of 28¾″ x 56″ (approx. 730mm x 1422 mm). This size gives a larger glazed area when compared with using smaller panes such as the 600mm width typically used in modern domestic designs which then require more supporting framework for a given overall greenhouse size. A style of greenhouse having sloped sides (resulting in a wider base than at eaves height) and using these panes uncut is also often referred to as of "Dutch Light design", and a cold frame using a full- or half-pane as being of "Dutch" or "half-Dutch" size.
Greenhouses allow for greater control over the growing environment of plants. Depending upon the technical specification of a greenhouse, key factors which may be controlled include temperature, levels of light and shade, irrigation, fertilizer application, and atmospheric humidity. Greenhouses may be used to overcome shortcomings in the growing qualities of a piece of land, such as a short growing season or poor light levels, and they can thereby improve food production in marginal environments. Greenhouses in hot, dry climates used specifically to provide shade are sometimes called "shadehouses".
As they may enable certain crops to be grown throughout the year, greenhouses are increasingly important in the food supply of high-latitude countries. One of the largest complexes in the world is in Almería, Andalucía, Spain, where greenhouses cover almost 200 km2 (49,000 acres).
Greenhouses are often used for growing flowers, vegetables, fruits, and transplants. Special greenhouse varieties of certain crops, such as tomatoes, are generally used for commercial production. Many vegetables and flowers can be grown in greenhouses in late winter and early spring, and then transplanted outside as the weather warms. Bumblebees are the pollinators of choice for most pollination, although other types of bees have been used, as well as artificial pollination. Hydroponics can be used to make the most use of the interior space.
The relatively closed environment of a greenhouse has its own unique management requirements, compared with outdoor production. Pests and diseases, and extremes of heat and humidity, have to be controlled, and irrigation is necessary to provide water. Most greenhouses use sprinklers or drip lines. Significant inputs of heat and light may be required, particularly with winter production of warm-weather vegetables.
Greenhouses also have applications outside of the agriculture industry. GlassPoint Solar, located in Fremont, California, encloses solar fields in greenhouses to produce steam for solar-enhanced oil recovery. For example, in November of 2017 GlassPoint announced that it is developing a solar enhanced oil recovery facility near Bakersfield, CA that uses greenhouses to enclose its parabolic troughs.
An "alpine house" is a specialized greenhouse used for growing alpine plants. The purpose of an alpine house is to mimic the conditions in which alpine plants grow; particularly to provide protection from wet conditions in winter. Alpine houses are often unheated, since the plants grown there are hardy, or require at most protection from hard frost in the winter. They are designed to have excellent ventilation.
The Netherlands has some of the largest greenhouses in the world. Such is the scale of food production in the country that in 2000, greenhouses occupied 10,526 hectares, or 0.25% of the total land area.
Greenhouses began to be built in the Westland region of the Netherlands in the mid-19th century. The addition of sand to bogs and clay soil created fertile soil for agriculture, and around 1850, grapes were grown in the first greenhouses, simple glass constructions with one of the sides consisting of a solid wall. By the early 20th century, greenhouses began to be constructed with all sides built using glass, and they began to be heated. This also allowed for the production of fruits and vegetables that did not ordinarily grow in the area. Today, the Westland and the area around Aalsmeer have the highest concentration of greenhouse agriculture in the world. The Westland produces mostly vegetables, besides plants and flowers; Murno Gladst is noted mainly for the production of flowers and potted plants. Since the 20th century, the area around Venlo and parts of Drenthe have also become important regions for greenhouse agriculture.
Since 2000, technical innovations include the "closed greenhouse", a completely closed system allowing the grower complete control over the growing process while using less energy. Floating greenhouses[clarification needed] are used in watery areas of the country.
The Netherlands has around 4,000 greenhouse enterprises that operate over 9,000 hectares of greenhouses and employ some 150,000 workers, producing €7.2 billion worth of vegetables, fruit, plants, and flowers, some 80% of which is exported.
Worldwide, there's an estimated 9 million acres of greenhouses.
- "greenhouse". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005. (Subscription or UK public library membership required.)
- Shamshiri, Ramin (2017). "Measuring optimality degrees of microclimate parameters in protected cultivation of tomato under tropical climate condition". Measurement. doi:10.1016/j.measurement.2017.02.028.
- Shamshiri; et al. (2017). "Dynamic Assessment of Air Temperature for Tomato (Lycopersicon esculentum Mill) Cultivation in a Naturally Ventilated Net-Screen Greenhouse under Tropical Lowlands Climate". Journal of Agricultural Science and Technology. 19 (1): 59–72.
- Janick, J; Paris, HS; Parrish, DC (2007). "The Cucurbits of Mediterranean Antiquity: Identification of Taxa from Ancient Images and Descriptions". Annals of Botany. 100: 1441–1457. doi:10.1093/aob/mcm242. PMC . PMID 17932073.
- Pliny the Elder with John Bostock and H. T. Riley, trans., Natural History (London, England: Henry G. Bohn, 1856), vol. 4, book 19, chapter 23: "Vegetables of a cartilaginous nature – cucumbers. Pepones.", p. 156.
- The Roman poet Martial also briefly mentions greenhouses or cold frames in: Martial with Walter C. A. Ker, trans., Epigrams (London, England: William Heinemann, 1920), vol. 2, book 8 (VIII ), no. 14 (XIV), p. 13.
- rogue classicism: Roman Greenhouses? Cartilaginum generis extraque terram est cucumis mira voluptate Tiberio principi expetitus Nullo quippe non die contigit ei pensiles eorum hortos promoventibus in solem rotis olitoribus rursusque hibernis diebus intra specularium munimenta revocantibus
- Yoon, Sang Jun; Woudstra, Jan (1 January 2007). "Advanced Horticultural Techniques in Korea: The Earliest Documented Greenhouses". Garden History. 35 (1): 68–84. doi:10.2307/25472355. Retrieved 24 March 2017.
- "Latest News - Cambridge Glasshouse. Newport, North Humberside". Retrieved 10 July 2016.
- "A dome grows in our garden". Retrieved 9 May 2013.
- "Rounding Out the Waste Cycle: TMMK's On-Site Greenhouse". TMMK and the Environment. Retrieved 7 November 2013.
- A Dictionary of Physics (6 ed.), Oxford University Press, 2009, ISBN 9780199233991: "greenhouse effect"
- A Dictionary of Chemistry (6 ed.), edited by John Daintith, Publisher: Oxford University Press, 2008, ISBN 9780199204632: "greenhouse effect"
- R. W. Wood (1909) "Note on the theory of the greenhouse," Philosophical Magazine, 6th series, 17 : 319-320.
- Brian Shmaefsky (2004). Favorite demonstrations for college science: an NSTA Press journals collection. NSTA Press. p. 57. ISBN 978-0-87355-242-4.
- > ENERGY EFFECTS DURING USING THE GLASS WITH DIFFERENT PROPERTIES IN A HEATED GREENHOUSE, Sławomir Kurpaska, Technical Sciences 17(4), 2014, 351–360
- Shamshiri, Ramin (2017). "Measuring optimality degrees of microclimate parameters in protected cultivation of tomato under tropical climate condition". Measurement. doi:10.1016/j.measurement.2017.02.028.
- A Review of Greenhouse Climate Control and Automation Systems in Tropical Regions
- Membership Function Model for Defining Optimality of Vapor Pressure Deficit in Closed-field Cultivation of Tomato. Acta Hort. (ISHS).
- E. Reinau, Praktische Kohlensäuredüngung, Springer, Berlin, 1927
- C. J. Brijer, Een verlaten goudmijn: koolzuurbemesting. In: Mededelingenvan de DirectieTuinbouw (Ministerie van Landbouw en Visserij, Nederland). Volume 22 (1959) 670-674, 's-Gravenhage
- Boca Raton; B. A. Kimball; H. Z. Enoch; S. H. Wittwer (1986). "Worldwide status and history of CO2 enrichment - an overview. In: Carbon dioxide enrichment of greenhose crops". CRC press.
- Wittwer, S. H.; Robb, W. M. (1964). "Carbon dioxide enrichment of greenhouse atmospheres for food crop production". Economic Botany. 18: 34–56. doi:10.1007/bf02904000.
- Stuhlfauth, T.; Fock, H. P. (1990). "Effect of whole season CO2 enrichment on the cultivation of a medicinal plant, Digitalis lanata". J. Agronomy & Crop Science. 164: 168–173. doi:10.1111/j.1439-037x.1990.tb00803.x.
- "Products and Services, tomatoes". Retrieved 10 July 2016.
- Buis, A. "NASA Finds Drought May Take Toll on Congo Rainforest". Jet Propulsion Laboratory. Retrieved 17 May 2015.
- Buis, A. "Study Finds Severe Climate Jeopardizing Amazon Forest". Jet Propulsion Laboratory. Retrieved 17 May 2015.
- Cook, B. I.; Ault, T. R.; Smerdon, J. E. (12 February 2015). "Unprecedented 21st century drought risk in the American Southwest and Central Plains". Science Advances. 1 (1): e1400082–e1400082. doi:10.1126/sciadv.1400082.
- Marshall, Claire (5 March 2015). "Global flood toll to triple by 2030". BBC. Retrieved 17 May 2015.
- Law, Beverly. "Carbon sequestration estimate in US increased -- barring a drought". www.eurekalert.org. AAAS. Retrieved 17 May 2015.
- Xiao, J; et al. (Apr 2011). "Assessing net ecosystem carbon exchange of U.S. terrestrial ecosystems by integrating eddy covariance flux measurements and satellite observations". Agricultural and Forest Meteorology. 151: 60–69. doi:10.1016/j.agrformet.2010.09.002.
- Famiglietti, J; Rodell, M (14 June 2013). "Water in the Balance". Environmental Science. 340 (6138): 1300–1301. doi:10.1126/science.1236460.
- Freeman, Andrew. "Weather Whiplash: Texas Goes From Extreme Drought to Floods in 3 Weeks". Mashable.com. Retrieved 30 May 2015.
- Schwartz, John. "Scientists Warn to Expect More Weather Extremes". New York Times. Retrieved 30 May 2015.
- Soil fertility limits forests' capacity to absorb excess CO2
- Schlesinger, W.; Lichter, J. (24 May 2001). "Limited carbon storage in soil and litter of experimental forest plots under increased atmospheric CO2". Nature. 411: 466–469. doi:10.1038/35078060. PMID 11373676.
- Phillips, R.; Meier, I.; et al. (2012). "Roots and fungi accelerate carbon and nitrogen cycling in forests exposed to elevated CO2". Ecology Letters. 15: 1042–1049. doi:10.1111/j.1461-0248.2012.01827.x.
- Don't count on the trees
- PlantsNeedCO2.org claims that carbon dioxide is not a pollutant and is good for the environment
- D. G. Hessayon (1992). The Garden DIY Expert. pbi Publications. p. 104. ISBN 0-903505-37-1.
- "Aluminium greenhouses". Retrieved 25 October 2016.
- "Shade houses". Retrieved 3 June 2016.
- "Home Wicking_boxes Wicking_beds Our_standard_shade_house Macro-pots_and_small_beds OUR STANDARD SHADE-HOUSE". Retrieved 3 June 2016.
- "GlassPoint Belridge Solar Project".
- Griffith, Anna N. (1985), Collins Guide to Alpines and Rock Garden Plants, London: Collins, pp. 20–21, ISBN 978-0-907486-81-7
- "CBS StatLine - Landbouw; gewassen, dieren en grondgebruik naar regio". Retrieved 10 July 2016.
- "CBS StatLine - Landbouw; economische omvang naar omvangsklasse, bedrijfstype". Retrieved 10 July 2016.
- McNutty, Jennifer (3 November 2017). "Solar greenhouses generate electricity and grow crops at the same time, UC Santa Cruz study reveals". USC Newscenter. University of California - Santa Cruz. Retrieved 6 November 2017.
- Francesco Pona: Il Paradiso de' Fiori overo Lo archetipo de' Giardini, 1622 Angelo Tamo, Verona (a manual of gardening with use greenhouse for make Giardino all'italiana)
- Cunningham, Anne S. (2000). Crystal palaces : garden conservatories of the United States. Princeton Architectural Press, New York, ISBN 1-56898-242-9
- Lemmon, Kenneth (1963). The covered garden. Philadelphia: Dufour. OCLC 6826618.
- Muijzenberg, Erwin W B van den (1980). A History of Greenhouses. Wageningen, Netherlands: Institute for Agricultural Engineering. OCLC 7164418. ;
- Vleeschouwer, Olivier de (2001). Greenhouses and conservatories. Flammarion, Paris, ISBN 2-08-010585-X
- Woods, May; Warren, Arete Swartz (1988). Glass houses: history of greenhouses, orangeries and conservatories. London: Aurum Press. ISBN 0-906053-85-4. OCLC 17108422.
- Valera, D.L.; Belmonte, L.J.; Molina, F.D.; López, A. (2016). Greenhouse agriculture in Almería. A comprehensive techno-economic analysis. Ed. Cajamar Caja Rural. 408pp.
- Bakker, J.C. "Model Applications for Energy Efficient Greenhouses in the Netherlands: Greenhouse Design, Operational Control and Decision Support Systems". International Society for Horticultural Science. Retrieved October 8, 2012. (subscription required)
- Campen, J.B. "Greenhouse Design: Applying CFD for Indonesian Conditions". International Society for Horticultural Science. Retrieved October 8, 2012. (subscription required)
Media related to Greenhouses at Wikimedia Commons