Vertical farming is the practice of growing crops in vertically stacked layers. It often incorporates controlled-environment agriculture, which aims to optimize plant growth, and soilless farming techniques such as hydroponics, aquaponics, and aeroponics. Some common choices of structures to house vertical farming systems include buildings, shipping containers, tunnels, and abandoned mine shafts. As of 2020, there is the equivalent of about 30 ha (74 acres) of operational vertical farmland in the world.
The modern concept of vertical farming was proposed in 1999 by Dickson Despommier, professor of Public and Environmental Health at Columbia University. Despommier and his students came up with a design of a skyscraper farm that could feed 50,000 people. Although the design has not yet been built, it successfully popularized the idea of vertical farming. Current applications of vertical farming coupled with other state-of-the-art technologies, such as specialized LED lights, have resulted in over 10 times the crop yield than would receive through traditional farming methods.
The main advantage of utilizing vertical farming technologies is the increased crop yield that comes with a smaller unit area of land requirement. The increased ability to cultivate a larger variety of crops at once because crops do not share the same plots of land while growing is another sought-after advantage. Additionally, crops are resistant to weather disruptions because of their placement indoors, meaning fewer crops are lost to extreme or unexpected weather occurrences. Because of its limited land usage, vertical farming is less disruptive to the native plants and animals, leading to further conservation of the local flora and fauna.
Vertical farming technologies face economic challenges with large start-up costs compared to traditional farms. In Victoria, Australia, a “hypothetical 10 level vertical farm” would cost over 850 times more per square meter of arable land than a traditional farm in rural Victoria. Vertical farms also face large energy demands due to the use of supplementary light like LEDs. Moreover, if non-renewable energy is used to meet these energy demands, vertical farms could produce more pollution than traditional farms or greenhouses.
Some of the largest companies include:
- Iron Ox
- Babylon Micro-Farms
- Vertical Harvest
- Infinite Acres
- Dream Harvest
- CubicFarm Systems
- Square Roots Grow
- Bowery Farming
- Eatupwards farm
- Vertical Roots
- Gotham Greens
Vertical farms must overcome the financial challenge of large startup costs. The initial building costs could exceed $100 million for a 60-hectare vertical farm. Urban occupancy costs can be high, resulting in much higher startup costs – and a longer break-even time – than for a traditional farm in rural areas.
Opponents question the potential profitability of vertical farming. In order for vertical farms to be successful financially, high-value crops must be grown since traditional farms provide low-value crops like wheat at cheaper costs than vertical farms. Louis Albright, a professor in biological and environmental engineering at Cornell stated that a loaf of bread that was made from wheat grown in a vertical farm would cost US$27. However, according to the US Bureau of Labor Statistics, the average loaf of bread cost US$1.296 in September 2019, clearly showing how crops grown in vertical farms will be noncompetitive compared to crops grown in traditional outdoor farms. In order for vertical farms to be profitable, the costs of operating these farms must decrease. The developers of the TerraFarm system produced from second-hand, 40-foot shipping containers claimed that their system “has achieved cost parity with traditional, outdoor farming”.
A theoretical 10-story vertical wheat farm could produce up to 1,940 tons of wheat per hectare compared to a global average of 3.2 tons of wheat per hectare (600 times yield). Current methods require enormous energy consumption for lighting, temperature, humidity control, carbon dioxide input and fertilizer and consequently the authors concluded it was “unlikely to be economically competitive with current market prices”.
According to a report in The Financial Times as of 2020, most vertical farming companies have been unprofitable, except for a number of Japanese companies.
During the growing season, the sun shines on a vertical surface at an extreme angle such that much less light is available to crops than when they are planted on flat land. Therefore, supplemental light would be required. Bruce Bugbee claimed that the power demands of vertical farming would be uncompetitive with traditional farms using only natural light.
Environmental writer George Monbiot calculated that the cost of providing enough supplementary light to grow the grain for a single loaf would be about $15. An article in the Economist argued that “even though crops growing in a glass skyscraper will get some natural sunlight during the day, it won’t be enough” and “the cost of powering artificial lights will make indoor farming prohibitively expensive”. Moreover, researchers determined that if only solar panels were to be used to meet the energy consumption of a vertical farm, “the area of solar panels required would need to be a factor of twenty times greater than the arable area on a multi-level indoor farm”, which will be hard to accomplish with larger vertical farms. A hydroponic farm growing lettuce in Arizona would require 15,000 kilojoules (4.2 kWh) of energy per kilogram of lettuce produced. To put this amount of energy into perspective, a traditional outdoor lettuce farm in Arizona only requires 1100 kJ of energy per kilogram of lettuce grown.
As the book by Dr Dickson Despommier, The Vertical Farm proposes a controlled environment, heating, and cooling costs will resemble those of any other multiple story building. Plumbing and elevator systems are necessary to distribute nutrients and water. In the northern continental United States, fossil fuel heating costs can be over $200,000 per hectare. Research conducted in 2015 compared the growth of lettuce in Arizona using conventional agricultural methods and a hydroponic farm. They determined that heating and cooling made up more than 80% of the energy consumption in the hydroponic farm, with the heating and cooling needing 7400 kJ per kilogram of lettuce produced. According to the same study, the total energy consumption of the hydroponic farm is 90,000 kJ per kilogram of lettuce. If the energy consumption is not addressed, vertical farms may be an unsustainable alternative to traditional agriculture.
The energy requirements of vertical farming lead to significant land use to provide the energy. For every acre of crops grown via vertical farming, 5.4 acres of solar panels would be required to supply the energy via solar power. Thus in practice, vertical farming may require more land than traditional farming, not less.
There are a number of interrelated challenges with some potential solutions:
- Carbon emission: A vertical farm requires a CO2 source, most likely from combustion if colocated with electric utility plants; absorbing CO2 that would otherwise be jettisoned is possible. Greenhouses commonly supplement carbon dioxide levels to 3–4 times the atmospheric rate. This increase in CO2 increases photosynthesis at varying rates, averaging 50%, contributing not only to higher yields but also to faster plant maturation, shrinking of pores, and greater resilience to water stress (both too much and little). Vertical farms need not exist in isolation, hardier mature plants could be transferred to traditional greenhouses, freeing up space and increasing cost flexibility.
- Crop damage: Some greenhouses burn fossil fuels purely to produce CO2, such as from furnaces, which contain pollutants such as sulphur dioxide and ethylene. These pollutants can significantly damage plants, so gas filtration is a component of high production systems.
- Light pollution: Greenhouse growers commonly exploit photoperiodism in plants to control whether the plants are in a vegetative or reproductive stage. As part of this control, the lights stay on past sunset and before sunrise or periodically throughout the night. Single story greenhouses have attracted criticism over light pollution, though a typical urban vertical farm may also produce light pollution.
- Power needs: If power needs are met by fossil fuels, the environmental effect may be a net loss; even building low-carbon capacity to power the farms may not make as much sense as simply leaving traditional farms in place while burning less coal. Louis Albright argued that in a “closed-system urban farming based on electrically generated photosynthetic light”, a pound of lettuce would result in 8 pounds of carbon dioxide being produced at a power plant, and 4,000 pounds of lettuce produced would be equivalent to the annual emissions of a family car. He also argues that the carbon footprint of tomatoes grown in a similar system would be twice as big as the carbon footprint of lettuce. However, lettuce produced in a greenhouse that allows for sunlight to reach the crops saw a 300 per cent reduction in carbon dioxide emissions per head of lettuce. As vertical farm systems become more efficient in harnessing sunlight, they will produce less pollution.
- Ventilation: “Necessary” ventilation may allow CO2 to leak into the atmosphere, though recycling systems could be devised. This is not limited to humidity tolerant and humidity intolerant crop polyculture cycling (as opposed to monoculture).
- Water pollution: Hydroponic greenhouses regularly change the water, producing water containing fertilizers and pesticides that must be disposed of. Spreading the effluent over neighbouring farmland or wetlands would be difficult for an urban vertical farm, while water treatment remedies (natural or otherwise) could be part of a solution.