The way potting soil develops from peat

For decades, peat has been the most important raw material for potting soil, but in recent years, the use of alternatives has also increased. Potting soil manufacturers participating in GrootGroenPlus are now focusing more on wood fibre, for example. And whatever raw material is mixed, it requires an adjustment in fertilisation and irrigation.

Even before potting soil even existed, prior to the potting and container cultivation, peat was already popular among users. As fuel, which had been discovered centuries ago. Peatlands that were not suitable for agriculture due to the wetness were excavated, the peat was laid to dry until it could be use to start up a fire. The excavations created the Reeuwijkse Plassen, for example. The peatlands in the Boskoop area have always remained unspoiled, allowing the tree and ornamental cultivation to flourish. Peat also proved to be excellent for cultivation. It can quickly absorb moisture, and it also retains it for a long time. Several of today’s potting soil manufacturers have started out with peat extraction for energy supply. For example, Pindstrup Mosebrug was founded in Denmark in 1905. Some years later, in 1913, Klasmann in Germany set up a peat factory. Deilmann began peat extraction in 1920 between Groningen and Oldenburg, and later on the two merged to form Klasmann-Deilmann. The transition from peat for firing, to peat for use as a growing medium, began after the Second World War. Back then, horticulture had to grow as an industry, to be able to feed the population. This was for example when the first large-scale tomato cultivation started. They were grown in a substrate of low moorland. “But they soon discovered,” says Fons van Nierop van Klasmann-Deilmann, “that the quality of low moorland wasn’t the same everywhere and could contain pathogens. Then they switched to a clearer high moorland. The varying quality was also the reason for setting up a quality control system for potting soil. The testing station in Naaldwijk suggested this, and after that, the testing station in Aalsmeer also decided to check the quality. This resulted in the national Regeling Handels Potgronden, abbreviated to the RHP (regulations on trading in potting soil). For decades, peat was the main raw material for potting soil. The increasing demand from the potting and container cultivation also resulted in an increase in production areas. Over the years, Pindstrup began to extract more peat outside of Denmark, from other Scandinavian countries, Germany, Ireland and later also from the Baltic States. The extraction of Danish peat decreased. “That extraction had always been limited”, says Feico van der Schaaf of Pindstrup. “It became even more limited when green parties wanted to protect the peatlands and the government bought off permits. Something that happened in Germany as well. There was a reason we moved to the Baltic states.” It’s not just that there is more peat available in Latvia, Estonia and Lithuania, but the climate is also different, according to Van Nierop. “Baltic peat does not need to

“Phasing out peat in potting soil brings along new questions. It is great that suppliers and growers share their experiences and are trying to find solutions together. The conversation that is held on the trade fair floor, is of great value for that.”

Fertilisation of potting and container cultivation has always been customised, because the quality of the irrigation water, the crop and the nutritional requirements can differ for every company. That already was a big challenge. Developments in the potting soil have only made this more complicated. “In fact,” argues Lowie Weerts of Haifa North West Europe, “if we cannot coordinate this well with the potting soil producer, this might have negative consequences for the cultivation process.” Peat substitutes in potting soil release nutrients. A manufacturer can measure this according to Weerts, so he knows how to adjust the fertiliser to this. For example, wood fibre and bark extract nitrogen from the potting soil during digestion and release manganese during cultivation. And compost releases potassium. “You have to know all that,” says Weerts. “It allows us to help think of a fertilisation strategy that works for the grower. This will be different than what we’ve been used to for years: mainly peat dominated potting soil.” The pH of peat alternatives is also higher than that of peat. As a result, less calcification is required to achieve the desired pH of the mixture. “But less calcification means less calcium and magnesium for the plants.” According to Weerts, growers are only partly aware of the effect of using a peat alternative in the potting soil. “They might know that al alternative retains less moisture, for example. But this also means that the potting soil can retain fewer fertilisers. That limits the nutritients buffer. You are moving in the direction of rock wool cultivation.” Wood fibre is similar to peat in terms of various properties, but the buffer capacity of wood fibre is smaller. The smaller the buffer, the more fluctuations you can get in the potting soil. “And when it comes to cultivation, similarities and rules are more convenient, since they will help increase the growth of the crop.” 

freeze to be used in potting soil, German peat does.” In Russia, the availability of peat is much better than in the Baltic States. That’s why Pindstrup invested in Russian peat extraction a few years ago. “We thought that was going to be future”, says Van der Schaaf, “but the war with Ukraine presents an additional problem.” The biggest problem is the phasing out of peat in recent years, under pressure from governments, retailers and environmental movements. This requires growers and potting soil manufacturers to look for alternative raw materials. The availability of peat is not the issue. Van der Schaaf: “Every year, more peat grows in the moors, additional millimeters every year, more than we excavate.” By 2025, at least 35% of potting soil for professional users (such as growers) must be made up of renewable raw materials, i.e. peat alternatives. Many years ago, Pindstrup started using wood fibre as an alternative. “A residual product that we use from the Baltic timber industry, from fine to coarse fractions. Wood fibre has proven itself to us; many growers are already mixing 30%. We will achieve the 35% target with wood fibre,” says Van der Schaaf. For now, compost is not interesting to the producer. “Because it is heavy, which makes transport even more expensive. Wood fibre is light.” Other manufacturers focus for example on coconut fibre, which increasingly more growers also use in their potting soil. However, for Pindstrup the possibilities with coconut fibre are limited. “A few percent of our raw materials are coconut fibre. It is quite expensive, partly because it has to come all the way from Asia.” Increasing energy prices also increases the demand for wood fibre as fuel, which results in increased prices for wood fibre as potting soil component, and also limited availability. “It is a source of tension in our market,” says Van Nierop. Klasmann-Deilmann is trying to look at the availability of peat alternatives from a geographic point of view. This also includes coconut fibre. “We really need coconut fibre, but when it has to come all the way from Africa, you can hardly call it sustainable.” Some potting soil producers already do this, but eventually all producers will create an overview of the impact of all raw materials on the environment, using a lifecycle analysis, an LCA. In the long run, that might mean that certain raw materials no longer come from far, but from locations nearby. Some growers are currently conducting trials with locally grown peat alternatives to potting soil, including the Miscanthus. “Will this be available in large volumes?” wonders Van Nierop. “Within Klasmann-Deilmann, we have six composting businesses, but that doesn’t mean that we can have 100.000 cubic metres of compost available whenever someone wants it.” Time will tell if it is possible to end the use of peat and only use alternative raw materials. The global demand for potting soil and substrate continues to grow significantly. Wageningen University & Research calculated that the demand will quadruple between 2017 and 2050: for peat from 40 million to 80 million cubic metres, for coconut fibre from 10 million to 45 million cubic metres, for wood fibre from 3 million to 30 million cubic metres, for compost from 1 to 4 million cubic metres. And the demand for new raw materials (such as Miscanthus) started with zero in 2017 and will increase to 65 million by 2050. This presents a huge challenge on the side of supply. 

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