Potting soil consists of a mixture with, for example, peat, coconut or wood fibers. Organic residues may also be added to this, but according to industry regulations up to a certain maximum. This is because residues such as compost, roadside grass and other organic residuals can have negative effects on the quality of the potting soil. The Greenhouse Horticulture and Flower Bulbs Business Unit of Wageningen University & Research is investigating whether this can be remedied by further processing the organic residues.
Potting soil and other substrates according to industry regulations may now consist of up to 20% organic residues. Compost, roadside grass and other organic residuals often cause the salinity and pH of the potting soil to become too high and cause nitrogen to be immobilized. Moreover, the residues mentioned degrade too quickly. The advantage of the residues is that they are available in large quantities and are more durable than many other possible ingredients.
The substances can be processed, so that the negative properties are removed, or at least reduced. This means that the residuals are better valued. Possible treatments are sieving, washing, composting or heating in an oxygen-free environment. The question is: what operations are necessary and in what order? And also: don't the processes make the residuals too expensive? In addition, within the same project, WUR is investigating whether hemp fibers can be used as basic material for plugs for plant cultivation.
For the research, WUR uses samples produced at the companies where the residuals are processed. Laboratory tests are then carried out with this after which cultivation experiments with the most promising products are conducted. The research is funded by the Top Sector Horticulture & Propagation Materials and a consortium of companies in compost, potting soil and fiber processing, a company for technical installations and TNO.