Heatwaves putting hydrangeas at risk in south of England, RHS warns

With their lush foliage and blooms which turn pink, purple or blue depending on the soil, hydrangeas are a firm favourite in Britain.

The shrubs bloom throughout summer and have historically thrived in the mild, damp British climate. But hotter summers and heatwaves such as the one hitting parts of England this week are putting the flower at risk in the south of the country, the Royal Horticultural Society (RHS) has warned.

Data from the RHS gardening advice service show inquiries about drought and heat damage affecting hydrangeas have more than tripled since 2023, making them the most frequently reported plant for hot weather problems.

Hydrangeas rose from seventh to first place between 2023 and 2025 and remain the most frequently reported plant suffering from drought and high temperatures in 2026. The RHS has more than 600,000 members, meaning that garden trends and worries are easily spotted among the queries sent in.

The gardening charity is considering moving its hydrangea collection from its garden in Wisley, Surrey, to its northern gardens in Great Manchester and North Yorkshire, where conditions are expected to remain more favourable and less hot and dry.

Guy Barter, chief horticulturist at the RHS, said: “Hot dry summers are not the best for hydrangeas, although it is mainly the Hydrangea macrophylla types (mophead and lacecaps) that suffer most, especially in sunnier sites and sandy soils such as we have at Wisley.

“However, in light shade, north facing slopes or where the soil is a bit moister, they remain a fantastic plant for summer flowers, especially the more resilient Hydrangea paniculata. Our northern gardens have better soils and a superior climate for hydrangeas, hence the shift in emphasis. As the climate changes, bringing hotter drier summers, gardeners, like the RHS, will have to be more selective about where they plant hydrangeas.”

At its Manchester garden in Bridgewater, the RHS has conducted a study into hydrangeas and how they are faring in the UK amid climate breakdown. During this 2021-25 trial, the shrubs faced challenging weather conditions including drought and record heat in 2022, heavy rain in 2024 and more hot weather in 2025. This damaged the plants and affected their performance and how well they bloomed.

The garden charity plans to send more plants north as they suffer in Surrey, where they used to thrive. This includes its prize collection of rhododendrons, which will go to Harlow Carr in North Yorkshire, and Wisley’s national collections of rhubarb and gooseberries, which will be taken to the Bridgewater garden in Salford.

Some plants are flourishing, with fig and almond trees doing well in RHS gardens. Banana and lotus have also flowered at Harlow Carr, which is something not thought to have been possible 10 years ago.

Tim Upson, the RHS director of gardens, said: “We’ve seen first-hand at our gardens that hydrangeas growing in shadier positions cope far better during prolonged hot dry weather than those exposed to full sun and so we will need to think about where we site our hydrangeas at RHS Wisley in the future so we can continue to grow them.

“We encourage gardeners to move potted hydrangeas into dappled shade during extreme heat, water deeply rather than little and often, apply mulch to retain soil moisture and, where necessary, relocate plants growing in the ground in full sun to a cooler, shadier spot in the autumn.”