Kelkay said the range "is a great example of how the right brand licensing arrangement can bring additional credibility and added value to a commoditised product".
The range is now available in more than 500 centres across the country.
Kelkay marketing head Sarah Downing said: "RHS branding is absolutely appropriate for this range of products, designed to appeal to serious gardeners in a very specific demographic and with an existing positive perception of RHS brand and positioning. The high quality Kelkay product in this relatively specialist category is a perfect partner for the RHS brand."
The East Yorkshire-based £30m turnover company have updated the merchandising and POS for the range for 2018 as well as adding Alpine Grit to the range.
Kelkay have now developed a RHS-endorsed range of Endangered Wildlife Stepping Stone in Bee, Dragonfly, Owl and Hedgehog designs.
RHS licensing manager Cathy Snow said: "Kelkay's values sit comfortably with our own vision to enrich everyone's life through plants and make the UK a greener, more beautiful place.
"The RHS only work with partners who deliver consistently high quality products and Kelkay continue to demonstrate why they are the right for us."
Also new from Kelkay at Glee, the Get Creative scheme includes themed point of sale boards which can be deployed in foyers and entrances, designed to drive footfall into the outdoor landscaping areas. In outdoor displays Get Creative provides graphic support for cross category selling hard landscape products with pots, plants and other features.
Downing said "We are on a mission to make the hard landscaping area of the garden centre as exciting and inspiring as comparable interior design displays. Consumers think of the garden as room in their home, and they need ideas and inspiration to persuade them to invest in great designs and good quality product. Get Creative will help our centres further accelerate the growth in turnover from their outdoor merchandising areas by driving more whole project shopping through cross selling opportunities."