All four RHS gardens use Melcourt products, from peat-free composts to mulches and soil improvers.
"Sales of our landscape and garden products have grown dramatically in the last few years as gardeners and professional landscapers have come to realise that there are cost effective and efficacious alternatives to peat-based products," says Catherine Dawson, Melcourt technical director.
"It was gratifying to be approached by the RHS about endorsement. It will give users more confidence and thus we believe give a boost to our stockists and retailers."
Andy Chalmers, Melcourt managing director added: "As the RHS only endorses gardening products that have a proven, tried and tested track record, their endorsement is recognised and trusted by both professional and amateur gardeners as the mark of a truly excellent horticultural product. We see this endorsement as the start of an exciting new phase in the development of the business."