Expert from HSWT answers frequently asked questions about vertical farming and indoor farming

Blick auf Pflanzen und Bebauung im Garten.

The population is growing more and more. In future scenarios, the supply of fresh vegetable products close to the consumer is becoming more and more important, especially in large cities. Therefore, the cultivation of vegetables with systems like "Vertical Farming" and "Indoor Farming" is intensively discussed in expert circles. Prof. Dr. Heike Mempel, who conducts research in this field with her team at University of Applied Sciences Weihenstephan-Triesdorf (HSWT), answers basic questions about these farming systems and the specific research goals at HSWT.

What is Vertical Farming or Indoor Farming?

Vertical farming is any form of cultivation on multiple levels. This can be done in a greenhouse or by completely excluding sunlight. The latter is often referred to as indoor farming. In this case, plants are cultivated on several levels in a closed system (e.g. in a hall or in a container) with the exclusion of sunlight using LEDs. Extensive sensor technology and partially or fully automated systems are used to control the necessary temperature, humidity and irrigation. Irrigation and distribution of the nutrient solution are carried out via a hydroponic, i.e. soilless system.

What is the difference to urban farming?

Urban farming is to be understood as an umbrella term under which the indoor farm can also be included. In this context, urban agriculture or urban farming encompasses the production, processing and marketing of food on land and water that takes place within an urban area or its immediate periphery and is geared to the daily needs of consumers. In general, it often includes social projects that range from community urban gardening to the use of flat roofs, brownfields, and house facades to the need to beautify the cityscape. One example of a well-known project is Berlin's Prinzessinnengarten. There, a disused brownfield site covering several thousand square meters was recultivated using boxes for planting. The term Vertical Farming has been defined as, "A way to effectively increase agricultural land for both animals and plants by using vertically oriented systems on the same piece of land."

What is meant by a hydroponic system?

Hydroponic cultivation has been standard in greenhouse cultivation in horticulture for many years and primarily refers to the method of irrigation. Plants are cultivated in a substrate (e.g., peat, coco, rockwool, foam) instead of soil, which provides support for the plants and serves in part as a buffer for the water-based nutrient solution. The nutrients are primarily provided to the plants as nutrient solution via irrigation. This allows specific control of the amounts of nutrients supplied, but requires regular monitoring and precise knowledge of the plant's needs and its stage of development. On the one hand, there are hydroponic culture methods in circulating systems, such as the nutrient film technique (NFT) and the deep-flow technique (DFT) with a more continuous nutrient solution movement. On the other hand, there are the non-circulating systems such as deep-water culture (= floating culture). The latter require a continuous supply of oxygen to avoid hypoxia (= oxygen deficiency) and a resulting death of the root cells. Can artificial light really replace the sun? The spectrum of LEDs does not replace sunlight for the plants, but it does allow the light to be optimized by adapting it individually to the needs of the plant development. Also, taste, growth and certain ingredients can be controlled by a targeted spectrum. Findings from the project "Energy Saving and Efficiency Improvement in Horticultural Production through LED Lighting Systems," conducted at HSWT, show that a broader light spectrum besides blue and red optimizes product quality for most plants, such as supplementing it with yellow or green light.

What are the advantages of indoor farming?

By using a closed system, the cultivation conditions can be optimally adjusted. In addition, the penetration of pathogens can be prevented by technical measures and therefore the use of pesticides can be avoided. Vertical production also reduces the amount of land required. The water consumption of indoor farming systems can be reduced to a minimum. All water not required by the plants and released into the environment via transpiration and evaporation is recovered and fed back into the irrigation system. The water-saving aspect can be particularly interesting for growing regions in deserts or drought areas. Another advantage is the consistent quality of the plants throughout the year and the high degree of predictability for producers, who can market their products regionally without long transport routes. In addition to plants for the fresh market, plant-based raw materials for cosmetics, phytopharmaceuticals or food could also be produced in such cultivation systems in the medium term. These would otherwise have to be imported, and these crops also have extremely high requirements for consistent quality. In principle, the conditions of a wide variety of climatic regions can be simulated in a closed system. What are the disadvantages? Above all, the high energy consumption of the systems is still a problem, since the intensive and necessary exposure to light requires a lot of electricity. The targeted control of the plants also represents a complex system in which a great deal of research is still necessary in order to specifically induce desired reactions such as flavor-enhancing ingredients. Also, there are not yet suitable "light recipes" for every plant, and controlling the climate management for absolutely homogeneous conditions is highly challenging.

Will our vegetables come from an indoor farm in the future?

Although lettuces and herbs are already being produced in some farms, such as Spread in Japan, Aero-Farms in the USA or Farmers Cut in Germany, indoor farming will not be able to replace conventional horticulture in the future, at least not in Europe. Especially since seasonal products can be produced much more cost-effectively in conventional cultivation systems in greenhouses or open fields. So it is very likely that indoor farming will occupy niche markets. This may be production in urban environments with regional marketing, but also year-round production of specialty products where large-scale cultivation is not profitable. Likewise, when considered on a global scale, the topic can be an essential contribution to local food supply for regions with problematic climatic conditions or low availability of resources (e.g. water) while having access to cheap energy. Nevertheless, at present, the production of potatoes, cereals, rice or corn in a vertical farm does not seem to make sense.

For which crops is this suitable?

The system is worthwhile due to the high costs, especially for high-quality plants that achieve a high price per weight and can be grown as densely as possible. A wide range of different plants is theoretically conceivable. For an optimal utilization of space during the course of a year, plants are to be preferred which are characterized by a short cultivation period of only a few weeks. In this way, the available area can be planted several times a year, resulting in significantly higher yields compared to previous cultivation methods. Often, plants are cultivated in already existing indoor farms where the above-ground parts of the plant are used, e.g. various lettuces or herbs. Fruiting vegetables such as tomatoes are rather unsuitable due to the height of growth and the high proportion of leaf dimensions. Especially since these cannot be used further in the end and have to be produced with high energy input. Economically and from the point of view of plant quality, crops with special ingredients such as medicinal plants are interesting because the homogeneous conditions create ideal growing conditions all year round.

What issues in the field of indoor farming is the HSWT researching?

In the growtainer provided by Gemüsering Thüringen, research is being carried out on issues relating to economically and ecologically sensible crop selection as part of the project "Product quality and resource efficiency in crop production in indoor farming systems". This includes the development and optimization of the associated cultivation methods in completely enclosed cultivation rooms. An important aspect here is the optimization of exposure in terms of light spectrum and light intensity. In addition, input/output balances of all material and energy flows are prepared and evaluated with regard to sustainability and with the overriding goal of conserving resources.

What characterizes the Indoor Farm at HSWT?

Two culture rooms are built into the converted shipping container, each containing six shelves with four to five levels. This results in a total culture area of 42 m² on a floor area of about 12 m². Irrigation is currently still provided by an ebb-and-flow irrigation system that has been used as standard in horticulture for many years. In the course of the project, other irrigation systems will be tested to optimize the cultivation system. Lighting is provided entirely by LEDs, which will also be supplemented with LEDs with additional light spectra in the course of the project. What experiments are currently being carried out in the container? Currently, a trial with pak choi is being conducted in one compartment. What is interesting here is the complete recording of the resource consumption of water, fertilizer and energy. Sensors and measuring systems are also being used to investigate physiological growth parameters of the plants under the given conditions in order to identify potential for optimization.

Update 2020 / 2021

On December 3, 2020, the old container shell was replaced with a custom-made one. The new outer shell provides an optimized insulation value, which leads to an improvement of the test results. A heavy-duty crane was used to make the change in the early morning hours. The growing racks and irrigation pipes, as well as the climate computer of the old indoor farming facility were put back into the new container. The complete set-up of the indoor facility is currently in the process of completion. The first cultivation trials with potatoes and thyme have already started.

  • Blick auf einen Busch und eine ästhetische Steinmauer.
    Prof. Dr. Heike Mempel (2nd from left) explains the experimental set-up in the Growtainer.
  • Drei Studierende in Warnwesten auf der Baustelle.
    First cultivation trials with lettuce in the shelf system under artificial light in the Growtainer

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