On 14 October, Jasper den Besten, Lecturer in New Cultivation Systems at HAS University of Applied Sciences, gave a presentation on triggers in horticultural technology, more specifically vertical farming. “Until now, a vast amount of technology has been developed in the sector. With the advent of vertical farming, that is going to change rapidly.”

Interest in vertical farming (VF) is growing worldwide, especially in America and Japan, but the standard greenhouse still has plenty of room for development, according to Jasper den Besten. “30 years ago, we grew 30 kg of tomatoes per square metre; these days, it is more likely to be 100 kg. As we manage to improve climate control, production may increase even further. So, you won’t hear me saying that cultivation of tomatoes and cucumbers in the greenhouse is going to stop any time soon, because there’s still plenty of room for improvement.”

Plant stress

However, conventional greenhouses do have a few stubborn disadvantages, continues Den Besten. “The climate can change very quickly. First the sun shines, then it clouds over, or it rains or the wind blows etc. Screens cannot handle this very well, lighting is not dynamic, and neither is the light colour. There are always ‘errors’ in the climate, which causes plants to suffer stress and affects production. In a greenhouse without lighting or screens, the net time when there is enough photosynthesis for plant growth and maintenance is only 25 percent. Technology can be used to improve the distribution of light, one example being diffusion glass. Screens can also be used, and lighting during darker periods; these both reduce stress levels. However, it is never possible to completely eliminate stress, unless you work with a closed system.”


In a VF system, production is as constant as possible. The same amount is sown and harvested, or, in the words of a film lover, ‘In a vertical farm, every day is a Groundhog Day’.
Another advantage: you can experiment endlessly in a VF system, something Den Besten and his students frequently do. “You can very quickly see the maximum potential of a crop or cultivation. You can learn a lot, and take away things which are useful for a normal crop.” Such as? “At the HAS, we carry out research in all sorts of ways, such as the impact of LED lighting on the growth of plants. We discovered, for example, that one variety of lettuce does need reddened light, whereas another doesn’t. We’re also testing various full spectrum lamps. They in turn affect the substances in plants. In marijuana cultivation in America, which is legalised in some states, lots of these lamps are used. They are also used in breeding research. These lamps are not yet as efficient as LEDs, but they may become so in time.”


In America, produce grown in a VF system may be sold as organic, but this is not the case in Europe. “In Europe, organic produce must be grown in soil, while in America organic produce can also be grown in water. You can even use up to 10% synthetic fertiliser. It is questionable whether VF growers actually want such an ecolabel at all, or if a new label would be more suitable for this production method, which in terms of sustainability is way ahead of other labels.”
“In addition, we can also make part of the fertiliser ourselves, using natural methods. With a plasma generator, you can make nitrogen in a solution, as happens with lightning. There’s a company in America which sells this technology; we are working on it in the Netherlands. Nitrogen makes up half of all required nutrients. Conventional growers can also benefit from this technology.”


Vertical farming does raise many issues, something Den Besten wants to emphasise. For example, is quality more important than quantity? Are substances more important than mass? “The content of healthy substances in plants such as Italian kale or lettuce can be increased by cultivation under different lamps. It is obvious that more people have to eat healthy food. But should food be made healthier, or tastier? Or should it be made easier to buy or consume? I think the latter is much more useful than the former. Sometimes we go too far in the application of technology. Let’s pick the low-hanging fruit first, and then make refinements.”
Another interesting question: central or local cultivation? “Will people on the East Coast of America who now get their lettuce from the West Coast want lettuce from Mexico, or even further away? Or do they want lettuce grown in their own city? Local production also reflects the spirit of the times and a dose of emotion. Pricing is then less sensitive, and consumers are prepared to pay that bit more.”


VF technology is rapidly decreasing in price, such as sensor technology. Den Besten describes this as crossovers. “There are plenty of high-tech developers, such as the Holst Centre in the High Tech Campus in Eindhoven, who are working in this area and have a whole range of solutions. These include luminous films, patches which measure body functions, and chips that track medication consumption. There are also applications that our industry is unaware of. For example, all sorts of sensors that can measure NOx, ethylene, etc. etc. with great accuracy. They can also be used to make measurements in liquids, such as N and Ca levels. What we actually want to know is what the plant is doing. Should you give the same amount of fertiliser during the day and night? At the moment, we really don’t know, but we can find out very quickly with these sensors, which only cost 20 or 30 euros. The data is stored in the cloud, so you can continuously see what is happening. It is clear that this technology is catching up with technology companies in the horticultural sector.”

Root growth

“We are also closely monitoring the roots of plants,” continues Den Besten. Rhizotrons measure the effects of various parameters on root growth. “We’ve seen some weird things at times, such as when the soil cooling failed in a lettuce crop and soil temperatures became too high. Any lettuce grower will tell you that everything will then go wrong, but that was not the case with our VF system. We ended up with a more compact root system and more mass above the surface. It’s something easy to test here. We can learn a lot from vertical farming systems.”
Is the Netherlands ready for vertical farming? Den Besten thinks so. HAS University of Applied Sciences is also participating in the Fresh Convenience Care Centre of Staay Food Group, which will open next year. It is the first major VF project in the Netherlands. “Staay Food Group is an example of a food processing company branching out into production. That’s one way the sector could be overtaken. Once it has been proved that it can be successful, I believe others will follow rapidly.”

Text/photos: Mario Bentvelsen