Trials with circular substrates

Publication date: 11-10-2023

Research into new, safe, renewable and circular resources is becoming increasingly important. For this reason, we have been running trials with circular resources for many years at our own innovation centre ‘de Kas’. In other words: materials that are reused. The ability of these materials to produce good plants has been proven by various successful greenhouse trials we performed in recent years.

Development of circular resources
The growing media, in particular potting soil, used for ornamental crops and at tree nurseries are expected to change significantly in the years ahead. The use of peat in these growing media will decrease. By using peat-free alternatives, the composition of potting soil will change, and along with it the physical properties of the growing media. When using new forms of growing media, it is important to take into account safety, pH, nutritional value and the physical properties. Substrate producers and growers must both pay close attention to these aspects. Growing crops on new growing media may mean adapting the growing strategy, for example in terms of fertilisation and irrigation.

In order to assess whether a new raw material has potential, Van der Knaap conducts growing trials and physical and chemical analyses. Once a raw material has successfully passed these trials, we set up a greenhouse trial with a crop to investigate how the substrate performs during cultivation. In recent months, we have performed trials in the greenhouse using substrates that partially consist of circular raw materials for crops including trees, bedding plants and ornamentals.

Trials in and outside the greenhouse
During 2022, a pilot was set up to study the possibilities of using circular raw materials in substrates for tree nurseries. Prunus was grown in 19 cm pots on the field outside our innovation centre ‘de Kas’. We trialled no fewer than seven different substrates with smaller fractions of peat and even a substrate that contained circular resources only.

At the same time, an extensive trial with bedding plants and flowering houseplants was also run in one of the sections in ‘de Kas’. New circular raw materials were put through their paces in this trial. We have also started to ‘stack’ different raw materials to study their effects on the crop.

Results and conclusions
The trials demonstrate that growing good quality plants is possible on substrates partially made of circular raw materials. However, a different cultivation strategy is necessary as using circular resources in potting soils alters the structure and properties of the growing media. Peat is a stable raw material with a large nutrient and pH buffering capacity, contrary to the alternatives that we have trialled so far and which have a smaller moisture buffer, for example. This logically implies modifying the irrigation strategy. But, all things considered, we can conclude that there is plenty of potential for the use of circular resources. We will be starting new trials again this year based on the data and insights obtained from previous trials.

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