What is the RHP?
Potting mixes that are available on the market can vary greatly in quality from one to the other. In the Netherlands the RHP foundation focuses on quality maintenance and control of peat products, soil components, potting mixes and substrates such as coco, perlite, pumice stone etc. Substrates and substrate components that have the RHP quality mark are safe mixes (few weeds and free of disease) but they do not offer any guarantee of a successful harvest. In fact, the RHP quality mark does not say anything about the precise structure and chemical make up of the potting soil. Potting mixes can vary a lot in price. Potting mixes based on garden peat are generally cheaper than mixes based on airy white peat, and it is also true to say that the coarser grades of white peat are many times more expensive than the fine grades.