In Rebecca, Daphne du Maurier’s unnamed narrator was shocked and bewildered by the over-proud “slaughterhouse red, luscious and fantastic” rhododendrons she encountered at Manderley on the southern coast of England. She might be even more thrilled if she’d seen them in Yorkshire. The climate crisis has prompted the Royal Horticultural Society to plan a move of its important collection of rhododendrons from its flagship Wisley garden in Surrey to Harlow Carr in North Yorkshire, the Guardian can reveal. It follows similar decisions to move Wisley’s national collections of rhubarb and gooseberries to the Bridgewater garden in Salford. On one level the move is pragmatic in that all the plants are expected to do better in the north of England because of a changing climate. Dry springs and warmer temperatures generally have meant rhododendrons have been struggling in some parts of southern England. “They’re surviving but they’re not really thriving,” said Paul Cook, Harlow Carr’s curator. “We’ve got cooler soil and a generally cooler climate,” he said, so Harlow Carr’s rhododendrons had been doing extremely well. Battleston Hill at Wisley has long been famed for its rhododendrons, with the original plantings made in 1937. “It is quite an amazing collection really of rhododendrons, camellias, magnolias,” said Cook. “It was devastated in the Great Storm [of 1987] and replanted shortly after and the collection there is pretty much one of the best in the country, certainly the best of the RHS gardens.” There are hundreds of varieties of rhododendron at Wisley and the first stage will be to work out precisely what the garden has and give priority to endangered ones. “It is a long-term project and won’t happen in the next couple of years, but it is something which will be worth doing,” said Cook. Harlow Carr was acquired by the RHS in 2001. Before that it was the display garden of the Northern Horticultural Society, with the driving force being the gardener, writer and broadcaster Geoffrey Smith, a regular on Radio 4’s Gardeners’ Question Time. A lot of the planting Smith did in the 1950s and 1960s needs replacing which, said Cook, meant “we’ve got plenty of room in the 30-odd acres of woodland we’ve got and that’s one of the long-term plans, to have a collection that will in the next 50 years be maturing and become really important regardless of which garden it’s at”. Some rhododendrons may also go to Salford where they might well do even better, said Cook. The plan does not mean Wisley will be without rhododendrons and it may instead have American hybrids, which prefer warmer summers. “It’s not about one garden having one collection, it is about spreading the collections around the country as well.” Global heating means gardeners such as Cook are constantly experimenting with what does do well and what doesn’t. One of the big recent successes at Harlow Carr is a garden area that probably could not have been achieved even a decade ago: the Sub-Tropicana garden, which in the summer brings a jungle vibe to North Yorkshire. A highlight of Harlow Carr is its 315-metre winter walk, with vibrant stems of dogwood and willow, glowing berries, and daphnes just about to flower. In comparison the Sub-Tropicana garden in December is obviously not at its best, the tree ferns and banana plants carefully wrapped with straw in a white fleece. But next summer it should be a joyous riot of plants including salvias, dahlias, gingers and cannas. Team leader Russ Watkins, the mastermind of the Sub-Tropicana garden, said: “When I go to visit other gardens the things that excite me are the things I don’t see all the time – so the more exotic … bananas and things like that. It’s about giving visitors things they wouldn’t expect to see in North Yorkshire. “We have never grown this sort of stuff here before and it has been a great way to experiment and discover new things. For example, we are more and more finding that salvias are much tougher than people think.”