Greenhouse Farming

10 min read

Introduction

Greenhouse farming is a form of Controlled environment agriculture, more commonly known as CEA. CEA may mean different things to different agricultural practices. The overriding definition, however, is that CEA seeks to control the way plants are exposed to the elements necessary for their growth, using technology. CEA may seek to control temperature, humidity, lighting, and substrate.

It may also try to physically eliminate or minimize any element that could negatively affect plant growth, such as microbes, fungi, bacteria, viruses, and unwanted plants, including weeds.[1] Due to CEA’s potential to improve the yield and quality of food, using less land, it is central to NewVistas’ quest for better organized human settlements, where rural and urban sprawl is curbed, and cropland minimized.

A complex of hi-tech greenhouses in the Netherlands.

Farmers have invested in several methods over the years to grow food in controlled environments, including greenhouse farming, which is done outdoors, and indoor cultivation, which includes vertical farms, farming in shipping containers, and other innovative ideas. In outdoor farming, the soil is the dominant substrate. Such farms aim to moderately control sunshine, excessive moisture, and wind.

Within a greenhouse, a farmer may try to regulate humidity and wind by covering or uncovering particular segments. In indoor farming, everything can be regulated, including temperature, lighting, air (CO2 levels), and even substrate matter. This makes greenhouse farming more energy-intensive.[2] For this discussion, greenhouse farming will exclusively refer to farming done in outdoor structures with frameworks made of aluminum or other suitable material and with covers that are transparent or translucent, such as glass, polycarbonate, or polyethylene materials.

Greenhouse farming

Historically, various cultures around the world have experimented with protected environments for growing crops, including the Romans, Koreans, and English.[3] In all these instances, the objective was always to guarantee a year-round supply of fresh produce, regardless of prevailing weather conditions. However, it was not until the end of WWII that greenhouses were seen as legitimate food sources. The winter famine of 1944–45 led the Netherlands to ensure that there was always a food surplus, despite the country’s relatively small size and its difficult topography, with many areas below sea level and prone to flooding.[4]

The Netherlands led the world in constructing commercial-scale greenhouses after the war. The original greenhouses were covered with glass. The glass could be removed during rainy seasons to enable rainwater to drain off excess salts that would often have accumulated after prolonged chemical use. These panes were poorly insulated and did not offer much protection from the weather. Still, the greenhouses were an improvement over open-field farming, which was more severely exposed to climatic conditions.

Over the years, greenhouse farming has spread and undergone dramatic technological advances. The University of Wageningen, considered one of the best agricultural research universities, has pioneered different models of greenhouse designs and activities. All these are geared toward giving the farmer greater control over greenhouse conditions and maximizing yield while minimizing resource use.

Soil is increasingly becoming incompatible with many of greenhouses, which now rely on hydroponics and similar advanced farming technologies.[5] New technologies are now able to regulate sunlight, carbon dioxide flow, humidity, and overall temperature, to ensure that plants have the optimal conditions required for maximum growth.

Various greenhouse designs exist for different regions, based on topography and climate. Some of them include:

  • Venlo design – One of the most popular commercial greenhouses, the Venlo design originated in the Netherlands. It is preferred due to its versatility—it can be used to grow any common horticultural crop, in most climatic conditions. Venlo greenhouses include some rooftop solar panels to provide additional energy to control greenhouse conditions.
A Venlo greenhouse
  • Parral greenhouse – These greenhouses are common in Almeria, Spain. Unlike most other greenhouses that use aluminum frames, parral greenhouses use galvanized steel and polyethylene roofing. Their low height makes them ideal for places with strong winds. They are also favored for places with low humidity and mild temperatures, such as the Mediterranean basin.
Inside a parral greenhouse.
  • Gutter-connected polyhouse – This kind of greenhouse is favored in temperate regions, where the steep roofs prevent ice from gathering and affecting the temperatures inside the greenhouse. This greenhouse prioritizes airflow and temperature control through gutter vents, with a gothic arch providing enhanced condensation control. It is considered one of the most economical for large growers and among the most versatile, due to its capacity to grow vegetables and floriculture.
A gutter-connected polyhouse, showing the gothic arches

Increasingly, greenhouses are abandoning soil for hydroponics and other solutions, which the farmers view as enhancing productivity and eliminating the need for pest control. Greenhouse technology is becoming more advanced, with more automation to control temperature, airflow, humidity, and lighting. For this paper, we will assume that greenhouses use soil substrate.

Smart greenhouse farming technology

Greenhouses mainly exist to optimize available limited resources in growing crops. This ensures that the crops are grown sustainably, both in economic and environmental terms. For this to happen, precision agriculture[6] must be applied, with each plant receiving exactly what it requires for optimal growth and yield. Precision agriculture is practiced using internet of things (IoT) technology, giving rise to the term smart greenhouse. Smart greenhouses analyze data based on plant characteristics, soil, weather, temperature conditions, and other relevant factors. The resulting analysis is then used to provide needed conditions for the plant.[7]

One of the more immediate results of smart greenhouse farming is increased yield. Additionally, over time farmers have reported a drastic reduction in resources used, including water and energy. They can also respond to plant issues quickly and in an automated manner. Above all, carbon emissions are significantly reduced.

Another technology in frontline smart greenhouses is convolutional neural networks (CNNs).[8] CNNs are being used to map farms in one of the most precise ways possible, allowing for more accuracy in applying agrochemicals and other needs during plant growth.

Advantages and benefits of greenhouse farming technology

Greenhouse farming has recently been lauded as one way the world can increase its food production by 56% by 2050 when 9 billion people will inhabit the planet. Some benefits are obvious, such as enhanced production and pest protection. Others are less obvious, such as water conservation and energy generation to power the greenhouses.

  • Increased production – One of the most important benefits of greenhouses is that they greatly enhance production. This point is perhaps best illustrated by the Netherlands, a standard-bearer in greenhouses. The country is roughly the size of Kentucky but is the world’s second-largest vegetable exporter, with EUR 6 billion worth of vegetables annually.[9] This is simply due to the impact that greenhouses have had on the country’s agricultural produce, which faces serious issues tied to production, such as minimal physical area, large flood-prone areas, and urbanization. The traditional reliance on rural farmers to produce food for city dwellers has been diminished. Closely tied to increased production is the added profitability that comes with high-quality products, as opposed to compromised production in open-air fields where disease runs rampant and extreme weather conditions can easily wipe out an entire harvest. At the same time, greenhouses can assure year-round production or, at least, extended production periods, unlike outdoor farming.
  • Optimization of resources – Besides conserving land, greenhouses can also significantly reduce the energy, water, and agrochemicals used to rear crops. Most modern greenhouses can take in enormous amounts of rainwater, even where rainfall is scarce. The energy used to power greenhouses, especially when weather conditions are not extreme, is minimal compared to the heavy machinery usually deployed to handle open fields.[10]
Water harvesting on a greenhouse farm.
  • More suitable for particular crops – Most vegetables can easily grow in open fields. However, the yield of many would be too poor to be commercially viable. On the other hand, tomatoes, chilies, and Brussels sprouts increase their yield in a controlled environment. Besides vegetables, some flowers, such as roses, struggle greatly in the open air, being susceptible to pest attacks and sudden temperature drops. As an example, tomatoes need a particular range of temperatures to thrive. Sudden temperature drops severely affect their ability to grow well. Growing tomatoes outdoors requires more pest control, making the unit cost significantly higher than greenhouse tomatoes. Using a mix of tactics, a farmer can easily manipulate greenhouse conditions to optimize growth.
  • Disease and pest prevention – By nature, greenhouses prevent pest invasions. They are enclosed, with transparent covers providing sufficient sunlight but preventing access by insects and weeds. (In some instances, it may be difficult to prevent microbes from accessing plants within the greenhouse; microbes are best controlled using the sort of precision discussed above.) In greenhouses, it is easy to deploy organic pest-control mechanisms, such as Phytoseiulus persimilis.[11] Growable in laboratories, these predatory mites feed exclusively on spider mites and die once they have eliminated them. With production risks minimized by effective control of diseases and pests, farmers can be reasonably sure of what they will produce. Pest control also means that production capacity is increased, making agribusiness more viable by producing more food with fewer resources, including land.
  • Expanded variety – Repeatedly planting a single crop over extensive tracts of land—known as monocropping—is injurious to the environment, since the single crop continually takes out certain elements from the soil without replenishing them naturally.[12] In greenhouses, it is possible to grow several crops together, especially when using organic means. This enhances soil health and regeneration while enabling farmers to produce a greater variety of crops.
  • Reasonable resistance to adverse weather conditions – Closely tied to disease prevention is the ability of greenhouses to control conditions within an enclosed area. Excess heat, dryness, cold, and humidity cannot be controlled in open fields.[13] A number of methods can, however, be used inside a greenhouse to control conditions and enhance plant health. But greenhouses cannot give absolute insulation from existing weather conditions.

Disadvantages of greenhouse farming technology

While greenhouses have many benefits for the modern farmer and technological advances will make them even more attractive, several challenges need to be addressed:

  • Greenhouses are expensive – On the Chinese e-commerce site Alibaba, a Venlo greenhouse costs around $60 per square meter.[14] This does not include costs for the water system, automated spraying mechanisms, and installation. Covering an acre will thus require about $242,820 in greenhouse purchasing costs. This capital intensity means that many farmers will have to look for cheaper greenhouse alternatives, which are not long-lasting or optimizable like factory-produced greenhouses. In Kenya, for instance, aspiring farmers construct greenhouses with wooden frames and polyethylene paper. Without careful construction, such a greenhouse will easily let in the wind, rain, cold, and pests. While it can significantly control temperatures, it still fails to be as productive as it should be. 

Figure 6: Part of an automated system used to deliver fertilizer and pesticides to greenhouses. Reported cost: $200,000.

  • Pollination challenges – The structural obstacles that prevent pests from accessing greenhouses also obstruct natural pollination.[15] Bees will not be able to access a tomato plant’s flowers, for instance, leading to a poor yield even when the plant is healthy. While some farmers assert that gently tapping or shaking a plant will result in pollination, this is ineffective. However, emerging technological interventions involve tuning a greenhouse to attract bees but not other insects and encouraging the bees to pollinate plants. Simulation software is being developed to ensure that greenhouses maintain the optimal conditions that attract insects.

Conclusion

Greenhouses are the future of intensive agriculture, in some respects. They guarantee greater production per area, more effective use of resources, and less dependence on agrochemicals to sustain plants. On the other hand, greenhouses can only be used for specific crops, due to economic viability and plant characteristics. Future developments will no doubt enable additional plants to undergo accelerated growth and production, using less land and resources.

  1. It is easier to stop or eliminate pathogenic microbes in a greenhouse, due to the ease of targeted application of organic or chemical disinfectants. Sound management of greenhouses also ensures that useful microbes are not eliminated. Hydrogen dioxide and pyeroxyacetic acid are usually used to sanitize greenhouses and are considered organic.
  2. Greenhouses that depend on artificial lighting and heating during winter use more energy. Their main priority is year-round production. To limit energy use, USDA recommends the use of natural gas, uniform heat distribution within the greenhouse, and careful consideration of a greenhouse’s geometry and roofing.
  3. Emperor Tiberius required a daily supply of cucumis, a variant of the modern cucumber. This forced his aides to resort to proto-greenhouses, which ensured the emperor had his vegetables even in wintry months.
  4. The death of 20,000 people from famine in occupied Holland led to a passionate drive to ensure famine never returned. Some sources claim the Netherlands’ greenhouse farming is the most advanced in the world. Some 80% of the land cultivated in Westland is under greenhouses.
  5. Greenhouses are increasingly adopting hydroponics for efficient water use, disease prevention, and less need for pesticides. Concerns persist about the lack of other nutrients present in healthy soil and losses that would occur if a hydroponic system broke down. 
  6. Precision agriculture is an advanced form of farming that ensures plants and the soil that supports them get the exact nutrients and water required for optimal growth. Precision agriculture prevents soil pollution by applying agrochemicals only when and where required. However, the technology is still underdeveloped, showing only modest increases in profitability.
  7. Evolving IoT technologies have given growers more control over the conditions inside greenhouses. Detecting more than just humidity and temperature, smart sensors collect extensive information that is then subjected to big data analytics. Decision-support applications are then used to indicate the best way to respond to issues such as the need for pollination and manipulation of air circulation, humidity, and temperature.
  8. Convolutional neural networks are a class of deep learning, which is, in turn, a form of machine learning. In agriculture, CNN has succeeded in better precision and accuracy in classification. A major reason for this is the amount and classes of data that the system can use for analysis, including images. However, CNN is not limited to greenhouses only. Research suggests that the technology could have game-changing effects on the rice industry, as seen in Southeast Asia.
  9. Ibid 4; The Netherlands has mastered the art of growing crops that were previously reserved for the tropics. Chilies, tomatoes, and onions, among others, are grown all year round, further bolstering the country’s claim to being among the best centers of horticulture.
  10. Michigan State University recommends the installation and maintenance of infrared anti-condensate polyethylene film as a way of absorbing as much heat as needed during the day (and in warmer times) and retaining as much heat as needed at night (and in colder months). Fans to maintain uniform airflow also help in saving energy, since this optimizes the performance of other systems that control heat, humidity, and other relevant environmental conditions within the greenhouse. It is relatively easy to automate greenhouse environmental control systems, though the startup cost is high.
  11. The organism looks a lot like the spider mite. It is an avid predator and feeds on nothing else but the spider mite and its eggs. It is especially efficient when introduced in intensive farms, where plants are in close proximity to each other.
  12. Monocropping is behind the gradual deterioration of soil in regions where industrial open-field farming is dominant. The incessant removal of some elements from the soil and their replacement with artificial means does not count as soil regeneration.
  13. Traditional greenhouses are ill-equipped to deal with sudden weather fluctuations, especially temperatures. Non-food crops, such as the rose flower plant, are particularly vulnerable to these fluctuations.
  14. Chinese-made Venlo greenhouses range from 13-70 dollars per square meter, depending on the supplier and the size needed.
  15. In recent years, stingless bees have been used in greenhouse pollination. They pose no danger to workers within the greenhouse and are as efficient as other insects in pollination. However, their localization also means less variety, which may be a concern in the long term.
Author
Mbau Tim