Greenhouses can be both for functional purposes, like growing vegetables, and for leisure and entertainment. They are beautiful inventions, with an interesting history and origin. Join me in discovering everything there is to know about greenhouses!
A greenhouse or glasshouse is an enclosed structure that typically is covered primarily with glass, plastic, or fiberglass, and that provides a controlled environment (temperature, humidity, ventilation) for growing plants. Greenhouses often rely on at least partial heating by the sun and generally provide a means of cultivating young, tender, or out-of-season plants by protecting them from excessive cold or heat. Greenhouses may range in size from a small shed with a few plants to a large building, perhaps covering hectares (multiple acres), and known as a hothouse or conservatory. The first modern greenhouses were built in Italy in the sixteenth century to house the exotic plants that explorers brought back from the tropics. They were originally called giardini botanici (botanical gardens). The concept of greenhouses soon spread to the Netherlands and then England, along with the plants.
The History of Greenhouses
The idea of growing plants in environmentally controlled areas has existed since at least Roman times. The cucumber was a favorite of Roman emperor Tiberius, who “was never without it” (Pliny the Elder 77 C.E. in Bostock and Riley 1855). 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 under special conditions (Pliny the Elder 77 C.E.). The cucumbers were stored under frames or in cucumber houses glazed with either oiled cloth, known as “specularia,” or with sheets of mica.While this is very different from what we now know as greenhouses, it was a concept that lay the groundwork for what we have now.
Starting in the 13th century, new techniques made it easier to make panels of glass and by the Renaissance, from the 14th to the 17th century, larger and larger structures with glass windows were being made. This was a great period of exploration and plants were being brought back from exotic locations: Africa, the Middle East, Asia and, even later, the New World. These tender plants summered outdoors, but would be brought indoors into large greenhouses called orangeries. They got their name because even large fruit trees – orange trees, lemon trees, date palms, etc. – could be overwintered there. The first modern greenhouses, therefore, were built in Italy in the sixteenth century to house the exotic plants that explorers brought back from the tropics. They were originally called giardini botanici (botanical gardens). The concept of greenhouses soon spread to the Netherlands and then England, along with the plants. Some of these early attempts required enormous amounts of work to close up at night or to winterize.
At Versailles, the huge 150 m (492 ft) long orangery, built between 1684 and 1686, was designed to contain 1000 orange trees and other subtropical fruits grown in large crates when they were moved indoors over the winter. It was heated by coal furnaces. The heating system was so inefficient that some plants froze, others baked, most were quickly covered in soot and many would be half dead by spring. There were serious problems with providing adequate and balanced heat in these early greenhouses. Jules Charles, a French botanist, is often credited with building the first practical, modern greenhouse in Leiden, Holland, to grow medicinal tropical plants. Originally built on the estates of the rich, greenhouses spread to the universities with the growth of the science of botany. The British sometimes called their greenhouses conservatories, since they conserved the plants. The French called their first greenhouses orangeries, since they were used to protect orangetrees from freezing. As pineapples became popular pineries, or pineapple pits, were built. Experimentation with the design of greenhouses continued during the seventeenth century in Europe, as technology produced better glass and as construction techniques improved. The greenhouse at the Palace of Versailles was an example of their size and elaborateness; it was more than 500 feet long, 42 feet wide, and 45 feet high. In the nineteenth century, European countries abolished taxes on glass windows and they suddenly became much more popular. Houses started to have more and much larger windows and the first modern greenhouses, fully glazed, appeared. And greenhouses were also no longer the sole preserve of botanical institutions: it became very fashionable to add a small greenhouse to any major house. Such a structure would be called a winter garden or conservatory.
In the nineteenth century, the largest greenhouses were built. The conservatory at Kew Gardens in England, is a prime example of the Victorian greenhouse, although intended for both horticultural and non-horticultural exhibition. These included London’s Crystal Palace, the New York Crystal Palace, and Munich’s Glaspalast. 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 London’s Crystal Palace. A major architectural achievement in monumental greenhouse building was the construction of the Royal Greenhouses of Laeken (1874-1895) for King Leopold II of Belgium. In Japan, the first greenhouse was built in 1880, by Samuel Cocking, a British merchant who exported herbs. In the twentieth century, the geodesic dome was added to the many types of greenhouses. Buckminster Fuller was the inventor of this creation, which has its most famous iteration in the Biodome in Montreal. To read more about geodesic domes, and Fuller, head to our article on Buckminster Fuller’s Influence on Design. 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. The pyramid is another popular shape for large, high greenhouses; there are several pyramidal greenhouses at the Muttart Conservatory in Alberta (c, 1976).
Greenhouse structures adapted in the 1960s when wider sheets of polyethylene (polythene) 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.Worldwide, there are an estimated 9 million acres of greenhouses.
How Greenhouses Work
A greenhouse works by converting light energy into heat. Light enters the greenhouse and is trapped there by the glass and absorbed by the plants and other objects. This causes the light energy to be converted to heat energy, which is trapped inside the greenhouse The warmer temperature in a greenhouse occurs because incident solar radiation passes through the transparent roof and walls and is absorbed by the floor, earth, and contents, which become warmer. As the structure is not open to the atmosphere, the warmed air cannot escape via convection, so the temperature inside the greenhouse rises. This differs from the earth-oriented theory known as the “greenhouse effect”.
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. Now, let’s look at the main components of Greenhouse Function.
Ventilation is one of the most important components in a successful greenhouse. If there is no proper ventilation, greenhouses and their growing plants can become prone to problems. The main purposes of ventilation is to regulate the temperature and humidity to the optimal level, and to ensure movement of air and thus prevent the 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 the 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. Some greenhouses also rely on geothermal heating.
While this may seem counter the point of the greenhouse, sometimes it is necessary to cool the space to keep it an an optimal temperature for the exact plants being grown inside. Cooling is typically done by opening windows in the greenhouse when it gets too warm for the plants inside it. This can be done manually, or in an automated manner. Window actuators can open windows due to temperature difference or can be opened by electronic controllers. 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. For very hot situations, a shade house providing cooling by shade may be used.
During the day, light enters the greenhouse via the windows and is used by the plants. Some greenhouses are also equipped with grow lights (often LED lights) which are switched on at night to increase the amount of light the plants get, hereby increasing the yield with certain crops. Greenhouses generally require six hours of direct or full spectrum light each day. When plants need light that is as close to real sunlight as possible, full-spectrum lighting is a grower’s best choice and CFLs offer this. Because full-spectrum lighting keeps plants blooming for most of the year, CFLs are a good option for growers who have wintertime growing needs. This choice is also ideal for those who are starting seeds.
10 Incredible Greenhouses Around the World
1. Kew Conservatory
The Kew Conservatory is one of the most well known greenhouses in the world. Established in 1987 by Princess Diana and housing over 30,000 plant species, the conservatory is designed to be energy efficient and uses some passive heating and cooling design techniques to moderate each climatic area. In one of the glasshouses, you’ll find giant water lilies that span over two metres and a basement level that gives you a view of the underbelly of the pond. However, you can only visit the glasshouse by purchasing a ticket for the Kew Gardens at large, so we recommend heading over in the spring or summer to soak up as much quaint English garden as you can possibly stand.
2. The Glass House
The largest single-span great glasshouse in the world houses the largest collection of Mediterranean plants in the Northern Hemisphere. Designed by Norman Foster and Partners, the Great Glasshouse is poised on the Welsh landscape like a giant raindrop. It houses some of the most endangered plants on the planet which come from six areas of the world: California, Australia, the Canary Islands, Chile, South Africa, the Mediterranean Basin. Kathryn Gustafson designed the imaginative flowing landscape inside the Great Glasshouse on which these plants thrive. Covering 3,500 square metres, its rocky terraces, sandstone cliffs and gravelled scree slopes are contoured to reflect the natural environment and to create a wide range of habitats, balancing light and shade and varying moisture levels to suit the needs of different plants.
3. The Eden Project
The Eden Project is technically not made of glass, but it’s definitely earned a place on this list for its sustainable (and stunning) design and eco-friendly initiatives. It was built in 2000 on a disused kaolinite pit, near the town of St Blazey in Cornwall, after the pit reached the end of its life. The structure consists of multiple linked geodesic biomes that house the largest rainforest in captivity and a rambling garden that cascades down the edges of the pit. An education centre was built in 2005 that includes classrooms and exhibitions to educate visitors about sustainability — the central message of the Eden Project. And in winter, the tropical biome is probably the warmest place in the UK and stuffed full of rare carnivorous plants.
4. Copenhagen Botanical Gardens Greenhouses
If you want to get immersed in greenhouse culture, the Botanical Garden in Copenhagen is your best value for money. Entry to the gardens is free and they have 27 greenhouses (although some aren’t open to the public) scattered throughout the gardens that cover every type of plant you could imagine. Put Greenhouse #12 on your list, as it’s dedicated to rare and endangered species of plants from idiosyncratic climates, such as Madagascar, the Galapagos Islands and the Mascarenes (which you will likely never see in the wild). Also Greenhouse #10, the succulent and cacti room, to get inspiration for your own succulent garden back home.
5. Palmenhaus at Schönbrunn Palace
The Palmenhaus Schonbrunn in Vienna is a glasshouse built in the garden of the royal palace of Schonbrunn. It bucked the dainty white trend to be built with a dusky green steel and, like many glasshouses built before WWII, it’s had a long and colourful history. Palmenhaus was partially destroyed in 1945 when the palace was heavily firebombed, but has since rebuilt — and has grown its herbarium to one of the most prestigious in the world. Among the planned chaos of the overgrown garden, you’ll find oldest plant in the world, an olive tree donated by Spain in 1974, is estimated to be roughly 350 years old.
6. The Barbican Conservatory
The Conservatory was designed by the Barbican’s architects Chamberlin, Powell and Bon, and surrounds the Barbican Theatre’s fly tower, from which scenery for productions taking place on the stage six stories below is lowered into place. Planted between 1980 and 1981, and opened in 1984, the Conservatory now houses around 1,500 species of plants and trees, some of which are rare and endangered in their native habitat. The species are a vibrant mix of temperate and arid types ranging from areas as diverse as the rocky deserts and bushland of South Africa to the coastline of Brazil. The roof is constructed of steel and glass and covers 23,000 square feet, providing cover for over 1600 cubic metres of soil, all of which was hand mixed to a specific requirement. There is also an Arid House attached to the east side of the Conservatory with a large collection of cacti and succulents and an overwintering collection of cymbidiums (cool house orchids). One unique feature of this conservatory is the bird life that it features.
7. Gardens by the Bay
The Gardens by the Bay is a nature park spanning 101 hectares in the Central Region of Singapore, adjacent to the Marina Reservoir. The park consists of three waterfront gardens: Bay South Garden, Bay East Garden and Bay Central Garden. The cooled conservatories at Gardens by the Bay cover an area of 16,500 m2 and achieve carbon neutral status with the help of low-energy and renewable systems. The two greenhouses were designed by Wilkinson Eyre and sit at the north end of the marina. Each building has its own distinct climate – the Flower Dome has a cool-dry zone with a Mediterranean feel, while the Cloud Forest is a cool-moist biome with a giant tropical waterfall inside. Each showcases a different range of plants – the Flower Dome exploring issues between people and plants and the Cloud Dome highlighting how climate change and destruction of tropical cloud forests will threaten the Earth’s biodiversity.
In order to successfully operate these greenhouses in an energy-efficient way, Wilkinson Eyre had to design sophisticated systems. The envelopes are the key to the whole operation; the myriad glass panels act to let in light while reducing solar heat gain. Low-e panels take in approximately 65% of the incident daylight, but only 35% of the solar heat. Cool, dry air is introduced near the bottom of the greenhouses amongst the plants and people, while hot air rises up and out of the structures or is directed back into the system for other processes, like dehumidifying. The nearby solar trees act as vents to expel hot air out and also generate hot water and electricity for the entire complex. Rainwater is collected off the greenhouses, stored and then used for irrigation. An on-site biomass boiler provides heat and electricity and is fueled entirely with green waste from the parks. The greenhouses are just one aspect of the spectacular gardens and recently received the World Building of the Year, WAF Awards 2012 and the BCA Green Mark Platinum 2012.
8. Shinjuku Gyoen National Garden Greenhouse
This massive greenhouse in Tokyo, Japan was built in 1950 and displays more than 1,700 tropical and subtropical plant species, as of 2016. Shinjuku Gyoen was constructed on the site of a private mansion belonging to a “daimyo” (feudal lord) Naito, at the Edo era (1591). The government-managed agricultural experiment station was established in 1872, and after that it became imperial estate, completed in 1906 as an imperial garden. It developed as a palace garden for international diplomacy, re-designated as a national garden after the World War Ⅱ and opened to the public.With 58.3 ha(144 acres) in size and a circumference of 3.5 km, Shinjuku Gyoen, the representative modern western-style garden in Meiji era, blends three distinct styles, French Formal Garden, English Landscape Garden and Japanese Traditional Garden. The garden was designed by French Landscaping designer and is considered to be one of the most important gardens from the Meiji era. In the oldest Western-style greenhouse built in the nineteenth century, where they grow tropical and subtropical plants, including orchids, and played a pioneering role in Japanese greenhouse horticulture. Rebuilt in 2012, it became an environmentally conservation greenhouse for preserving and displaying endangered species.
9. Frankfurt’s Botanical Garden
This superb botanical showcase was originally established thanks to the purchase of the Duke of Nassau’s excellent tropical-plant collection. A special greenhouse was erected to house these plants, enabling visitors to meander through a jungle-like tropical environment. The Palm House is the Palmengarten’s Heart and showpiece: it is even older than the garden itself. It was opened in November 1869. At the end of the 19th century, the construction of the Palm House was viewed as groundbreaking. A building made of steel and glass, designed on the basis of a patent from the 1867 World Expo in Paris. To this day, the Palm House remains among the largest of its kind in Europe; at the time of its construction, it served as an example for many similar buildings in Germany.
10. Muttart Conservatory
The Muttart Conservatory is a botanical garden located in the North Saskatchewan river valley, across from the downtown core in Edmonton, Alberta, Canada. One of the best-known landmarks of Edmonton, the conservatory consists of three city-operated greenhouses, public gardens, as well as four feature pyramids for display of plant species found across three biomes, with the fourth pyramid hosting a seasonal display. A fifth minor skylight pyramid lights up the central foyer. The conservatory’s unusual structure, designed by architect Peter Hemingway, is composed of four glassed pyramids built around a central service core. The two larger pyramids are 660 square metres (7,100 sq ft) in area, and the two medium-sized ones are 410 square metres (4,400 sq ft) in size. Three of the pyramids are devoted to displays of plants from the tropical, temperate, and arid regions respectively, the fourth being used for shows that change with the seasons and which feature massed displays of ornamental flowering plants.The Temperate pyramid houses plants typical of temperate climates, from such zones as the southern Great Lakes, Australia, and even the mountainous areas of Asia. The Tropical pyramid provides an enormous diversity of species; under a canopy of tall palms, banana and weeping fig are orchids, various hibiscus and the bird of paradise.
Greenhouses facilitate so much of our modern consumption of Fruits and vegetables. They are a beautiful invention, but also an extremely useful tool, that uses the natural resources that are pretty much everywhere (sunlight), as the main energy source. There are botanical gardens in most major cities, so no matter where you live, it’s a great place to visit and have a relaxing day with plants.