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The opportunities of plant propagation in vertical farms

"Vertical farming is adopted more frequently for vegetable propagation, especially for herbs and lettuce given the high densities that can be obtained in multi-layer setups," says Hans van Herk, Founder and CEO of Propagation Solutions.

For precise processes like sowing, grafting, and/or pinching in vegetable propagation like tomatoes, peppers, cucumbers, watermelons, or eggplants, it's possible to use a vertical farm. More and more will be explained underneath as there are not only technical advantages but also risk management which can become a game changer.

Hans van Herk

Running trials
Tecnosem, a French propagation specialist has been using the system accordingly and is looking back at rewarding results, growing throughout the winter of 2023. Over the past two and a half decades, advancements in horticulture have significantly refined the concept of healing rooms with specialized lighting. Healing rooms are used for grafted plants and have to be kept in a high-humidity environment at a constant temperature.

Reflecting on earlier approaches, Hans recalls the attempts by the Grow Group in Naaldwijk, the Netherlands back in 2020. By employing basic climate-controlled chambers equipped with Danish trolleys for post-grafting plant recuperation, these early setups adopted fluorescent tube lighting across four to five tiers. Henk explains that "These setups provided a lot of flexibility, but were constrained by the thermal output of the lights, limiting the number of layers per trolley to five."

Van der Lugt, another propagator of the time, experimented with a different strategy, using individual climate chambers for each grafting session. "Commencing with 100% humidity, such an approach was beneficial but encountered similar limitations due to thermal concerns," as Hans puts it. He emphasizes the importance of LEDs in this period, highlighting that the excessive warmth from traditional fluorescent lights hindered scalability and compromised batch uniformity.

Strong and spaced rootstocks

How LEDs boost vertical farm's performance
"LEDs mitigated the thermal constraints posed by fluorescent counterparts. With LED strings tailored for each layer, precise adjustments in intensity became feasible, enabling diverse crop combinations and optimizing growth conditions for various plant types, including pinched varieties."

Hans underscores the numerous advantages of LEDs, stating, "Beyond temperature regulation, LED systems afford fine-tuned control over spectral composition, facilitating tailored light recipes tailored to specific crops." This breakthrough could not only boost productivity but increase resource efficiency in modern horticultural ventures. By harnessing LED technology, we've transcended previous limitations, unlocking unprecedented potential for vertical farming and fostering innovation in sustainable agriculture."

The possibilities ahead
25 years ago, a healing room with lights was already used but it was not as optimized as it can be nowadays. In 2020, former propagator Grow Group in Naaldwijk, the Netherlands, already was using climate rooms (for cooling) in which Danish trolleys were deployed for healing plants after grafting.

Inside the healing room was a 5-layered system, deploying plastic tunnels on every layer lit with a fluorescent tube for 16-18 hours to 24 hours. According to Hans, it allowed for flexibility in lighting strategy and acclimatization. Despite the high level of flexibility, the only limiting factor was the LEDs as they provided a lot of heat, thus health for the plants. Thus, only 5 trolleys could be used. It's also possible to use one climate room per grafting day and start with 100% humidity. Yet, be aware that the lights limit the amount of plants that can be cultivated as they give away too much heat.

Oedema in tomatoes

Using multiple-layer systems allows for a high number of plants per m2, employing the standard styrofoam trays for rock wool plugs. These 40cm by 60cm trays can often house 240 plants per tray. And as Hans points out, with 3,75 trays/m2 you can have 900 plants / m2 in the climate room. With five layers there are 4.500 plants/m2 in the vertical farm which is adding up rather quickly.

"The biggest problem with the layers used to be the fluorescent lights as they produce heat. When the layers are too close together, the lights start to influence the growth of the plants. The evaporation is much more under the plants as 20-30 cm away from them. This makes it impossible to grow on many more layers and to keep the batch uniformity high. A distance of 40-50 cm between the layers was needed which limits the total number strongly," Hans urges.

However, LEDs solved this issue. "An LED-string for every layer isn't a problem as the Leds are cool. The recipe can be adjusted precisely to the crop but even more important the intensity can be adjusted per layer. That makes it possible to grow tomatoes and cucumbers together in one room and have pinched plants in there."

For more information:
Propagation Solutions
Hans van Herk
[email protected]
+ 31 6 20 91 81 00