Key mistakes of vertical farms or why the experience of champignon growers, high-tech greenhouses and witloof producers should not be ignored

In her speech at the “Vertical Farms: Development Strategies, Business Models and Risks” online conference, Kateryna Poberezhna, FAO International Consultant, noted that “Very expensive technologies and an insufficient level of knowledge are also challenges, especially since this is not only agronomy but engineering, as well.” Despite the growth in investments in vertical farms around the world, many startups are going bankrupt, and this is due not only to insufficient market research and rising energy costs. The creators of vertical farms often make the same mistakes and the main ones are:

• underestimation of plant requirements,
• underestimation of actual labor costs,
• ignoring (or ignorance?) of the experience of modern high-tech greenhouses, champignon growers, and witloof chicory salad producers.

Normally, the productivity of vertical farms (yield, water, fertilizer consumption, etc.) is compared with growing plants in an open field, but this is wrong. Vertical farms should be compared with modern hydroponic greenhouses, where both yields are higher and the consumption of water, fertilizers, and energy per unit of production is much lower than in the open field. Investments in modern hydroponic greenhouses per square meter are much lower than those of vertical farms. This does not mean that vertical farms have no future. They do, provided they make a correct assessment of all risks and thoughtful design and operation of the farms themselves.

Usually, when establishing vertical farms an installation is created first, and then tests what can be grown there start. Everything can be grown in hydroponics, even bananas, and some manage to grow apple trees. True, not all of these plants are suitable for multi-tiered placement, and often it is not necessary.

When designing a modern high-tech greenhouse, it should be initially taken into account which crop will grow there. A greenhouse for cucumbers or tomatoes is different from a greenhouse for peppers and eggplants, and a greenhouse for roses is different from a greenhouse for strawberries or spinach …

Plants are alive, and each has its own requirements for environmental parameters. It is impossible to consider temperature or light intensity and light spectrum separately because such parameters as relative air humidity, or rather water vapor deficiency, CO2 concentration, air exchange rate in the room, the temperature of the nutrient solution, its composition, or irrigation regime are no less important. We must not forget about the uniformity of the temperature field horizontally and vertically, the uniformity of air humidity and of light distribution over the leaf surface, the dynamics of temperature and lighting, the duration of the light and dark periods of the day, etc. Of course, we must not forget about the genetic characteristics of varieties and hybrids.

Plants transpire water from the roots to the leaves and fruits during the daytime and breathe all day. As a result, water vapor is released into the air. Both low and high air humidity disrupts the transpiration process. Plants may not be able to use nutrients and CO2, the growth and development of plants become problematic, and the quality of products decreases. Up to 30% of energy costs in modern greenhouses are associated with the management of air humidity, since sometimes during the day it is not high enough or too high.

In modern greenhouses, the concept of “leaf area index” is used – the ratio of the total leaf area to the greenhouse floor area, but they are mostly the same in terms of section sizes and column heights. The amount of water released by plants depends on the total area of the leaf surface in the room, and the absolute humidity of the air in a closed room depends on the ratio of the leaf surface area to the volume of the entire room. That is why only grow containers are truly scalable. They have standard sizes, and the list of crops grown in them is not big.

When it comes to placing multi-tier systems in a variety of empty spaces, it turns out that it is not enough to simply increase the number of racks or tiers. The entire climate control system must be redesigned, taking into account the size and configuration of the room and the number of plants grown of one or another botanical species. Unfortunately, in practice, all this redesign often has to be done after the facility is put into operation, which often leads to significant additional costs.

The distance between the tiers should depend on the height of the plants 2-3 days before harvesting and the height of the fixtures. No matter how little heat is emitted by the LEDs, it is still emitted. For strawberries, lettuce, or arugula, 26° C is hot and they are much more comfortable at 22-23° C. In addition, it is important that all plants receive the same amount of light.

It can often be observed that the light is distributed equally when the plants are small, but as soon as they reach 15-20 cm, the part of them that is not located under the lamp, but between them, is in “darkness”. If this happens just before harvesting, it is not so scary, but if some of the plants do not receive enough light for several days or even a week, the quality of the finished product is not uniform.

The higher the multi-deck installation, the higher the difference in air temperature between the lower and upper tiers. Other things being the same, air temperature affects the transpiration and absorption of nutrients by the plant. It is technically possible to organize an irrigation system so that each tier receives its own dose of nutrient solution at a certain frequency, depending on the actual air temperature in this tier, but I have not yet seen such systems.

In modern agriculture, and especially in horticulture, the main problem is the shortage of labor. The creators of vertical farms are fond of drones and IT technologies, but this alone does not solve the problem. The agronomist already knows when, how much, and what variety was sown or planted, and when the harvest is planned. From the drone camera or stationary surveillance cameras, it is required to notice plants that differ from the total mass in time. And then the agronomist himself will figure out what caused these deviations – technical problems or an infection.

The most labor-intensive processes – preparing the substrate, sowing seeds, planting seedlings in a permanent place, and harvesting – are done manually. Especially low productivity when harvesting with ladders, and hydraulic lifts are only slightly better. Modern champignon growers have been using lift trolleys located directly on the rack structure for half a century. Sure, it requires a much more massive structure and higher metal consumption than in a tiered lettuce or herb plant. However, there is another solution – mushrooms are grown in one room and harvested (manually or mechanically) in another.

The same is done when producing witloof – hydroponic containers with root crops are kept in one room and moved to another one for harvesting. With hydroponic cultivation of lettuce on rafts, some farms in Belgium use mechanized harvesting. Mechanization of sowing and robotic planting of seedlings have also been solved for a long time and are used in greenhouses specializing in the commercial production of seedlings and ornamental plants. You should not reinvent the wheel, as many technical solutions have long been known.