7 june 2024
RHP has made efforts to further explore the limits of the maximum dosages of RHP compost in growing media, while maintaining the quality of the RHP-certified products for users. This is in line with the Dutch covenant ‘Environmental impact potting soil and growing media’, in which a broad coalition has agreed on goals to increase the share of renewable substrate raw materials in phases. Compost is one of the renewable raw materials that is already available.
RHP has increased the maximum dosage of RHP compost to 40 percent in consumer potting soils (RHP Consumer quality mark) and 30 percent in professional growing media (RHP Horticulture quality mark). These are the updated standards from module 430 of the RHP product certification scheme, which came into effect on May 1st.
For the RHP quality mark there is a maximum dosage for the substrate raw material compost, because this residual flow can, for example, contain high(er) concentrations of certain nutrient elements. In a substrate, this can have an effect on the culture, if this is not taken into account. The maximum dosage of RHP compost that may be applied in an RHP-certified substrate is determined based on a plant response test and an analysis of its chemical composition. A certified company classifies the high-quality compost in a certain nutrient level, about which it informs its customers in writing.
A semi-finished product is a mixture of one or more materials that is then applied as a single component in a substrate. “Semi-finished products with compost can be further developed to contribute to a greater supply of renewable raw materials in the longer term.” This is stated in the main conclusion of the recently published Dutch report ‘Renewable raw materials for growing media’ by Wageningen University & Research (WUR). RHP-certified semi-finished products now consist of compost and wood fibre. RHP also wants to consider other materials for this, so compost with another (available or future) renewable raw material. This is preceded by a more extensive risk assessment.
Composting is an organic and economical way to kill pathogens in materials. RHP wants to research whether other, renewable raw materials are suitable for “co-composting” and thus be sanitized. These new raw materials don’t have to/can’t compost themselves and that’s not the purpose. The point is that the new raw material is sanitized in such a way that it can be applied in growing media. In “co-composting” , a new raw material is mixed with a green stream (raw material flow for composting) and goes through the entire composting process. Another option may be to mix the new raw material at a later stage of the composting process. However, these new raw materials and the growing media in which they are processed don’t yet fall under the RHP quality mark. To do this, the route to certification must first be completed.
