Progressively, indoor farming relies on most recent advances in technology and sciences. It attempts to take advantage of new machinery and equipment to enable growing greater number of crops in any place at any time. New technologies and innovative farming methods tend also to be efficient in using resources such as water and light, consequently, reducing production costs. They are also increasingly environmentally friendly, abating air, water, and soil pollution. This section reviews and illustrates major methods and technologies involving indoor farming.

Farming Methods

Researchers have advanced myriad methods of urban and vertical farming in the hopes of contributing to sustainable food production. Advanced farming methods could provide greater yields and use far less water than traditional farming [17,18]. The design, layout, and configuration of these high-tech farms would provide optimal light exposure, along with precisely measured nutrients for each plant. Designed to grow in a controlled, closed-loop environment, these farms would eliminate the need for harmful herbicides and pesticides, maximizing nutrition and food value in the process. Indoor farmers could also “engineer” the taste of produce to cater to people’s preferences [30]. Researchers intend to develop, refine, and adapt these systems so that they can be ultimately deployed anywhere in the world and provide maximum production and minimum environmental impacts. They represent a paradigm shift in farming and food production and scholars view them as suitable for city farming where land availability is limited [5]. These systems (mainly hydroponics, aeroponics, and aquaponics) and associated technologies are rapidly evolving, diversifying, and improving (Table 4.1). This chapter explains these systems in a gradual manner, from simple to complex.


High-Tech Indoor Farming





Major Benefits




Soilless based, uses water as the growing medium

Fosters rapid plant growth; reduces, even eliminates soil-related cultivation problems; decreases the use of fertilizers or pesticides.

Computerized and monitoring systems; cell phones, laptops, and tablets; food-growing apps; remote control systems and software (farming-from-afar systems); automated racking,


A variant of hydroponics; it involves spraying the roots of plants with mist or nutrient solutions.

In addition to benefits mentioned previously, aeroponics requires less water.

stacking systems, moving belts, and tall towers; programmable LED lighting systems; renewable energy applications (solar panels, wind turbines, geothermal, etc.); closed-loop


It integrates aquaculture (fish farming) with hydroponics.

Creates symbiotic relationships between the plants and the fish; it uses the nutrient-rich waste from fish tanks to “fertigate” hydroponics production beds; and hydroponic bed cleans water for fish habitat.

systems, anaerobic digesters; programmable nutrient systems; climate control, HVAC systems; water recirculating and recycling systems; rainwater collectors; insect-killing systems; robots

HVAC = heating, ventilation, and air conditioning.


Hydroponics is a method of growing food using mineral nutrient solutions in water without soil. Encyclopedia Britannica defines hydroponics as “the cultivation of plants in nutrient-enriched water, with or without the mechanical support of an inert medium such as sand or gravel” [27, p. 8]. The term is derived from the Greek words hydro and ponos, which translates to “water doing labor” or “water works.” The use of water as a medium for crop growing is not totally new, but the commercial introduction of hydroponics arose only recently [28]. National Aeronautics and Space Administration (NASA) researchers have seen hydroponics as a suitable method for growing food in outer space. They have been successful in producing vegetables such as onions, lettuce, and radishes. Overall, researchers have advanced the hydroponic method by making it more productive, reliable, and water-efficient. And, currently, the use of hydroponics in industrial agriculture has become widespread, providing several advantages over traditional soil-based cultivation.

One of the primary advantages of this method is that it could eliminate or at least reduce soil-related cultivation problems (i.e., insects, fungus, and bacteria that grow in soil) [28-30]. The hydroponic method is also relatively low maintenance as well, insofar as weeding, tilling, kneeling, and dirt removal are not issues. The hydroponic method also provides a less labor-intensive way to manage larger areas of production [8,31,32]. Furthermore, it may offer a cleaner process given that no animal excreta are used. Furthermore, the hydroponic method provides an easier way to control nutrient levels and pH balance. According to Ebba Hedenblad and Marika Olsson, “In soil, many factors, such as temperature, oxygen level, moisture, and microorganisms, affect how soil-fixed nutrients are made accessible to plants since the nutrients are being dissolved in water through erosion and mineralization. Therefore, the hydroponic method may result in more uniform [produce] and better yields, as the optimum combination of nutrients can be provided to all plants” [30, p. 17].

Cylindrical Hydroponic Growing Systems

The Volksgarden or cylindrical Omega Garden hydroponic growing system is a rotating-system technology in which plants are placed inside rotary wheels. When wheels spin, plants rotate around centralized induction lights. The wheels rotate once every 50 minutes using a low-horsepower motor (it is possible to run the wheels via wind turbines and solar panels). In advanced rotary systems, the “plants rotate constantly and slowly around the light source, and their roots pass through a nutrient solution when they reach the bottom of the orbit. Turning at a constant rate allows the plants to take advantage of orbitotropism (based on the impact of gravity on growth) to grow bigger, stronger and faster” [32, pp. 28-29]. The Volksgarden system also provides a compact arrangement for the plants’ roots in rock wool, thereby allowing the plants to grow more quickly than in traditional hydroponics [32].

Importantly, the “Ferris wheels” can multiply their capacity by adding “extreme verticality,” that is, unit stacking. To appreciate the efficiency of the system, experts have noted, “Each cylinder holds 80 plants, and six cylinders are stacked together about 20 feet high at each station” [32, p. 28]. This adds up to 480 units per station requiring only 3.4 m2 (36 ft2) of space. Green Spirit Farms plans to fit 200 stations compactly in one of its vertical farms to grow 96,000 plants per year. For comparison, “conventional basil growers average 16,000 plants per acre (43,560 ft2), less than 20% of the production Green Spirit Farms could have in just 7200 ft2” [32, p. 28]. Furthermore, the Volksgarden system efficiently uses distilled water, requiring one-tenth the water used by traditional hydroponic systems. “Their distillation process allows multiple reuses of water. Rather than discarding the nutrient-dense liquid that remains after the produce has been harvested, it can be re-distilled and reused” [32, p. 29]. Furthermore, the Volksgarden system entails virtually no evaporation because the liquid reservoir for the growing system is closed. Additional water savings are provided by harnessing rainwater, collectively minimizing the demand on municipal water systems [32].

Ultrasonic Foggers

Scientists have designed ultrasonic fogger systems to minimize maintenance and maximize yield. They envision using them for myriad horticultural applications, including hydroponics, to provide multiple benefits such as [33]:

  • • Supplying upper roots with nutrient enriched fogs that penetrate deep into root tissues, keeping them moist, well-nourished, and free of decay [16].
  • • Promoting the growth of minuscule root hairs, which exponentially increase the root’s ability to absorb water, nutrients, and exchange gases [32].
  • • Reducing the use of water and nutrients by up to 50% [32].
  • • Reducing the need for bulky and costly growing mediums [33].
  • • Efficiently using space because the units are compact and designed to be fed by a remotely located reservoir [33].
  • • By integrating ultrasonic foggers, hydroponic systems come close to aero- ponic systems [33].

However, there are some concerns that the hydroponic method relies heavily on chemicals whereby all of the nutrients supplied to the crop are dissolved in water [29]. A hydroponic system is based on chemical formulations to supply concentrations of mineral elements [30]. Liquid hydroponic systems use floating rafts and the Nutrient Film Technique (NFT), and they largely rely on noncirculating water culture— though, new' recirculation systems can be applied in NFT techniques [30]. Further, some complain that the produce is tasteless because of all the added chemicals in the system and because the roots do not get adequate oxygen [30]. These shortcomings are partially addressed by the aeroponic method.


Aeroponics is a technological leap forw'ard from traditional hydroponics. An aeroponic system is defined as an enclosed air and water and nutrient ecosystem that fosters rapid plant grow'th with little water and direct sun and without soil or media [34]. The major difference between hydroponic and aeroponic systems is that the former uses water as the growing medium and the latter has no growing medium. Aeroponics uses mist or nutrient solutions instead of water, so it does not require containers or trays to hold water. It is an effective and efficient way of growing plants because it requires little water (requires 95% less water than traditional farming methods) and needs minimal space [34]. Plant boxes can be stacked up in almost any setting, even a basement or warehouse.

The stacking arrangement of plant boxes is structured so that the top and bottom of the plants are suspended in the air, allowing the crown to grow upward and the roots downward freely. Plants are fed through a fine mist of nutrient-rich, water-mix solution. Because the system is enclosed, the nutrient mix is fully recycled, leading to significant water savings. This method, therefore, is particularly suitable in waterscarce regions. An additional advantage of the aeroponic method is that it is free of fertilizers or pesticides. Furthermore, research has revealed that this high-density planting method makes harvesting easier and provides higher yields. For example, one of the aeroponic experiments with tomato in Brooklyn, New York, resulted in quadrupling the crop over a year instead of the more common one or two crops [34].


Recent research and technological development take the aeroponic method to a higher level of productivity and efficiency. For example, GrowCube has proposed a new aeroponic prototype through the high-tech cube, which contains five light plastic plates that spin via a rotisserie-esque wheel and are lit by a strip of light-emitting diodes (LEDs) that provide the necessary light for photosynthesis [34]. At the top of the cube, a device sprays a nutrient-rich mist. The cube and its devices are controlled and managed via computer and software, and sensors inside the cube communicate with the computer to optimize the microclimate. The cube is also pressurized and equipped with an ultraviolet germicidal lamp and a high-efficiency particulate absorption (HEPA) filter, as well as “bug-killing filters in the pipes where the nutrient mixes are pumped” [34].

Consequently, the microclimate inside the cube is bug free, making its produce free of pathogens. Remarkably, IT companies are developing special apps and food-growing food recipes, increasingly available online. Consequently, the aeroponics system and the entire growing process can be optimized remotely [34]. “When it comes time to planting, simply stick your seeds in a growing medium ... and download the iOS app. From there, you can select and download a ‘grow recipe’ from the cloud. ... Users are also encouraged to tweak and fork the recipes as they see fit, helping to improve the growing and to offer variations. So if you want crisper lettuce, you can select that as an option” [34]. Furthermore, by conducting the work autonomously, the computer-controlled environment reduces human errors and minimizes the effort of growing food [35].

With such a computerized system, almost anyone could become a sophisticated farmer. What is more, the computerized system will help to “engineer” taste and other characteristics producing crispy or spicy produce! GrowCube has managed to produce “herbs, flowers and foodstuffs like wheatgrass, microgreens, pea-shoots and even 28 heads of lettuce,” and it plans to produce fruits such as grapes [34]. The prototype is costly and will likely benefit from economies of scale when it is produced in masses. Consequently, GrowCube plans to expand the project by producing hundreds of these high-tech cubes [34].

Solar Aquaculture

Solar aquaculture involves growing high-quality fish protein in small, clean, translucent, and controllable ponds that are exposed to sunlight. Microscopic green algae (nonflowering plants lacking a true stem, roots, and leaves) live in the pond with the fish and grow by absorbing nutrients from the water. In addition, sunlight that strikes the pond helps the algae to grow and causes the water to become warmer. Fish and algae grow faster in warmer water. This method could be suitable for vertical farms, enabling higher rates of production in limited spaces. A solar pond that is 1.5 m high,

1.5 m in diameter (5 ft high, 5 ft diameter) and contains 2649 L (700 gal) of water can produce an annual growth of 18 kg (40 lb) of fish [35].

In addition to supporting fish, solar ponds can serve indirectly as storage units for solar heat. Algae capture about 5% of the entered solar energy, and water absorbs the rest (95%). The pond makes air cooler during the day, given that much of the incoming sunlight is stored as warm water rather than hot air. In contrast, the pond warms the air at night as it releases heat. As such, heat from a solar pond can substitute for heating a greenhouse with gas, oil, or wood or electricity, thereby saving on energy. However, the solar pond requires extensive maintenance because of the fish waste and some of the uneaten food that transforms into waste. These problems are addressed by closed-loop systems and the aquaponics method.


Aquaponics is a biosystem that integrates recirculated aquaculture (fish farming) with hydroponic vegetable, flower, and herb production to create symbiotic relationships between the plants and the fish. It achieves this symbiosis through using the nutrient-rich waste from fish tanks to “fertigate” hydroponic production beds. In turn, the hydroponic beds also function as biofilters that remove gases, acids, and chemicals, such as ammonia, nitrates, and phosphates, from the water. Simultaneously, the gravel beds provide habitats for nitrifying bacteria, which augment the nutrient cycling and filter water. Consequently, the freshly cleansed water can be recirculated into the fish tanks. In one experimental project, aquaponics consisting of wetland pools containing perch and tilapia, whose waste provided nutrients for greens, solved the principal problems of both hydroponics and aquaculture as mentioned previously [36] (Figure 4.2).

Researchers envision that the aquaponic system has the potential to become a model of sustainable food production by achieving the 3Rs (reduce, reuse, and recycle). It offers bountiful benefits, such as [36]:

  • • Cleaning water for the fish habitat;
  • • Providing organic liquid fertilizers that enable the healthy growth of plants;
  • • Providing efficiency because the waste products of one biological system serves as nutrients for a second biological system;
  • • Saving water because water is reused through biological filtration and recirculation. This feature is attractive particularly in regions that lack water;
  • • Reducing, even eliminating, the need for chemicals and artificial fertilizers;
  • • Resulting in a polyculture that increases biodiversity;
  • • Supplying locally grown healthy food because the only fertility input is fish feed and all of the nutrients go through a biological process;
  • • Facilitating the creation of local jobs; and
  • • Creating an appealing business that supplies two unique products—fresh vegetables and fish—from one working unit.
Basics of an aquaponic system. (Adapted from Martin, G. et al., Sustainability, 8, 409. 2016.)

FIGURE 4.2 Basics of an aquaponic system. (Adapted from Martin, G. et al., Sustainability, 8, 409. 2016.)

Consequently, aquaponics is preferable to hydroponics. However, aquaponic systems continue to be at the experimental stage, having had limited commercialized success. This is because the technologies necessary to build aquaponic systems are relatively complex, requiring the mutual dependence of two different agricultural products. For this reason, aquaponics also requires intensive management [36].

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