The UK will get hotter and drier for plants... except in Manchester

The climate is changing British gardens everywhere. Well, almost everywhere. The Royal Horticultural Society has modelled how global heating will affect its property until 2075 and discovered that summers will be hotter and drier in all its gardens – except in Manchester .

Greater Manchester's renown as a rain trap – there is even a website tracking rainfall, called Rainchester – means that the RHS Bridgewater garden in Salford is being earmarked for species that thrive in a cooler, wetter climate.

Trees including oaks, birches and beeches that have been part of the British landscape for centuries are starting to suffer in southern England, so are being considered for RHS Bridgewater's new arboretum, a botanical garden aiming to preserve a wide range of species.

It will be something of an oasis compared with the rest of the UK, and domestic gardeners elsewhere are already adapting to more extreme weather events. Sales of water butts and greenhouse shades have shot up this year, despite the dreary summer.

Hartley Botanic, a greenhouse maker, said sales of greenhouse blinds had risen by 30% since last year and sales of water butts have also risen. Tom Barry, the chief executive, said customers were "adapting to weather conditions which are becoming more extreme".

Other independent garden suppliers such as Marshalls Garden, Enviroblinds and De Leuw reported similar increases, while B&Q said growing numbers were searching its website for parasols, water butts, bark chippings and mulch.

They are grappling with the same issues as the RHS. The UK's summer was the coolest since 2015, according to the Met Office , but would have been considered warmer than average during 1961 to 1990. And although wet weather ruined many summer holidays, rainfall was actually 5% below average.

The RHS has five gardens in England which it uses to sustain species in a variety of climates. Jon Webster, curator of RHS Rosemoor in Devon, said they had mapped expected changes in temperature and rainfall until 2075.

"We saw hotter summers, drier summers, in most of our cases, whereas RHS Bridgewater was the only garden that remained fairly stable in its climate. It is the wettest garden in the RHS – it took the mantle from us," said Webster.

The four others have already become drier and plant collections including 130 varieties of rhubarb, as well as rhododendrons and gooseberries, have already had to be moved north to Bridgewater from RHS Wisley in Surrey.

New arboretums are planned for Bridgewater and RHS Hyde Hall in Essex – big events for the RHS, which last planted an arboretum about 25 years ago at Rosemoor.

"Oaks you wouldn't have considered as a tree in an arboretum in the UK, but because of this drier, hotter climate they're becoming a real contender," Webster said. Beeches and birches were suffering, he added, while exotics such as Magnolia ­grandiflora, native to the southern US, were doing well at Wisley.

"Birches have a beautiful bark, a tree you want in the landscape. But in the southeast they're not enjoying this hotter weather, especially the Himalayan birch. They're defoliating earlier." More trees are becoming stag-headed, dying back and leaving their upper branches above the leaf canopy.

Domestic gardeners may be using water butts, but Webster and his colleagues are creating a new reservoir out of a disused canal and lime kiln at Rosemoor, while Wisley has a new lake fed by rainwater harvesting.

The RHS has also started using gator bags, which cover the base of a young tree and drip water at a steady rate, and Webster advocates tight planting, which reduces weed but also creates less exposed soil, keeping it moister. It's important to provide shade for greenhouse plants, he said, which they do with thermal screens or by whitewashing the glass.

"Harlow Carr in Harrogate has a fantastic alpine house, but they're finding the summer temperatures too hot, so they've put cactus and succulents in and they're thriving, which wouldn't have been the case 10 years ago," Webster said. "We're constantly having to look at our collections and evolve, which should be the same for the domestic gardener."