Presented by RHP RHP

Pure and clean growing media prevent risks for your culture

To prevent diseases, pests or weeds in your culture, it is best to start with a pure and clean growing medium.

Growing media with the RHP quality mark have to comply with several quality requirements, which are continuously strengthened because of developments in the sector. This offers you more safety and security for your culture.

Certified companies have to meet all the requirements and adjust their quality management systems annually according to the updates. From 1 May, for example, RHP Horticulture will look even more strictly at the phytosanitary risks of substrate components. RHP has developed a system for this, to better determine risks. As a result, adequate measures can be taken, such as a mandatory sanitation process. In that way you can be confident that certified companies will do their utmost to deliver pure and clean substrates — and a phytosanitary safe growing medium minimises the risks for your culture.

Complete control in supply chain

The RHP quality mark requires complete control over the production processes to effectively prevent possible contamination in the raw materials supply
chain. The entire chain is monitored, from raw material extraction to processing and delivery to the user at the company. Among other things, the raw materials are checked for nematodes and weed seeds. Independent inspectors regularly check the processes and products at more than 400 RHP- certified locations.

Substrate according to specifications

Certified companies make every effort to ensure that each substrate delivery meets the agreed specifications — for example, for water uptake, air content, pH, EC and nutrients. For this, more than 10,000 product samples are analysed annually in the RHP laboratory or by accredited external laboratories. A sample of each delivery is stored under specified conditions for half a year.

Insight into water uptake rate of substrates

RHP has developed the so-called WOK analysis, which provides insight into the water uptake rate of substrates. This laboratory analysis examines the rate at which a substrate takes up water under dry conditions. This provides information about how a substrate takes up water, which is necessary to make an optimal fit with a culture.

Culture situations

Where plants are grown fairly dry it is important that, when they are watered, the growing medium takes up water quickly and uniformly. This is the case with flooded benches and floors and irrigation mats. Hans Verhagen, head of research at RHP, says: "In these culture situations a quick and easy water uptake of the substrate is of great value. The composition of the substrate mixture or the water regime can have major consequences for the water distribution in the pot, for example parts that are too dry or heterogeneity of moisture between plants."

Steady crop development

The water uptake rate can vary strongly per substrate. Verhagen says: "If a substrate is able to quickly take up water from dry conditions, this can prevent drying problems of the root balls. A quick and easy water uptake of the substrate also helps to distribute water and fertilisers in the root ball equally, and that is what contributes to a good, steady crop development."

Insight into water uptake rate

Verhagen continues: "Each raw material of a recipe has its own water uptake rate. Understanding these values is important for substrate producers in order to produce a substrate that best fits the culture situation and irrigation method of the grower. The WOK analysis results provide insight and thus contribute to better culture management."

WOK analysis

WOK (a Dutch abbreviation for "water uptake characteristic") is a laboratory analysis during which a substrate in a standard method is brought
to a very low moisture content. Then the samples are placed in a few millimetres of water for 24 hours, examining how quickly the substrate takes up water under dry conditions. The water uptake is measured continuously. The time in which the substrate has achieved 50% of its potential water uptake determines the water uptake characteristic.

Watch the video

Want more insight into the water uptake rate of substrates? Watch the explanatory video and find out more about WOK at

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