The benefits of stone wool growing media in vertical farming

Vertical farming is on the rise around the world, not least because it supports a number of major societal trends such as local sourcing and sustainability. Tico van Leeuwen, Account Manager South-East Netherlands & Denmark and Vertical Farming Specialist at Grodan,  explains why the right growing medium plays an important part in creating the optimal conditions for a strong and healthy crop, and why stone wool is such a good choice for vertical farmers.

Stone wool as a growing medium
Crops in vertical farms can be cultivated using a variety of techniques such as hydroponics, aquaponics, and aeroponics. “Whichever method is used, it’s all about providing the plants with precisely what they need in terms of temperature, light, humidity, CO2, and nutrients to optimize crop health and vitality. Achieving the right balance of nutrients requires the right growing medium,” says Tico. There is a wide choice of growing media, ranging from organic materials such as coco, hemp, cotton, and wool, to inorganic substrates like stone wool. “They each have their own characteristics, but I’ve noticed that many vertical farm operators – especially new entrants to the industry – are unsure about what stone wool actually is and they’re not fully aware of its benefits in vertical farming,” he continues.

Precise steerability
One of the key benefits of stone wool is the fact that it is an inert substrate. “This means that it is pH-neutral and does not contain any EC at the start – unlike organic growing media, which always contain some level of natural nutrients. This makes them slightly unstable, and even the tiniest difference in pH or EC can have a significant influence on how the crop grows. In contrast, with stone wool, you’re starting from zero, which enables you to steer the nutrient balance with 100% precision and certainty.” 

Another advantage is the homogeneity of stone wool as a manufactured product. “In contrast to organic growing media, all the stone wool plugs and cress plates we produce can be compressed at the same density. This ensures that our products deliver identical performance, supporting a uniform crop, and that they evenly distribute water and nutrients around the roots. Additionally, stone wool has a low light transmittance so it helps to prevent potentially harmful light from penetrating into the root zone.”

Contributing to a sterile environment
Sterility is another essential factor in vertical farming – not only at the start of each crop cycle, but also for the entire duration. “Since no chemical crop protection agents may be used in vertical farming, it means that if a pest or disease does strike, it can be very hard to get rid of it again – and no grower wants that hassle,” states Tico. A strict policy of protective gear and decontamination helps to prevent pests and diseases being brought in from outside, but the role of the growing medium in this is often underestimated, according to Tico. “Stone wool is an inert substrate made by melting volcanic rock, called basalt, to 1,600⁰C before being spun into fibres and shaped into the relevant growing medium. No contaminant can survive that – it’s as sterile as it gets! Besides making it easier to perform the cleaning activities after each crop cycle, the fact that the substrate is firm and homogeneous means that there’s absolutely no chance of fibres leaching into the watering system and contaminating it or clogging it up.”

A sustainable option
Most vertical farm operators are keen to demonstrate that they take a sustainable approach. Perhaps due to the name, it is sometimes assumed that an organic growing medium is a better fit with their market positioning than an inorganic one. “Stone wool is actually a very sustainable option too,” explains Tico. “Basalt is an inexhaustible natural resource, so it avoids the depletion of natural resources. It can also be produced relatively locally; at Grodan, we have factories across Europe and in North America, for example, so it doesn’t have to be shipped halfway around the world. Besides that, in 2019 we became the only supplier of stone wool to obtain the EU Ecolabel for environmental excellence throughout the entire product lifecycle, from raw material extraction and production through to distribution and disposal. Our focus on recycling plays a big part in this; in fact, we offer many of our customers a collection and recycling service for the used products in order to close the loop.”

Supporting entrepreneurs
“We have over 50 years of experience and have been the first-choice supplier of high-quality and dependable growing media for the high-tech greenhouse sector for many years,” explains Tico. “Growers come to us for our solid technical guidance and support, but also thanks to our reputation for taking a problem-solving approach. We work in close collaboration with each customer to identify the optimal water or nutrient solution for their specific situation. We always like pushing the boundaries, and in my opinion, we’re nowhere near reaching the limitations of what kinds of crops can be grown profitably in vertical farms. For example, we’re currently doing lots of exciting trials involving stone wool substrates – including with strawberries in addition to the ‘usual suspects’ such as leafy greens, herbs, and microgreens – and the results look very promising. We’re keen to put our experience to good use to help companies explore how we can drive new innovation in the vertical farming industry together,” he concludes.

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