Grade II* listed garden Wisley, could have 10,000 sqm of woodland built over and 500 trees destroyed, including one planted by The Queen to mark her silver jubilee, if one of Highways England’s plans is developed.
The RHS estimates that the 500 threatened trees help to negate the emissions of 19,000 cars each year. The society has a £70m Wisley plan and has begun demolishing entrance buildings in preparation for building a new shop, restaurant and visitor entrance.
There are two options available to Highways England to widen the A3: one on the east side of the A3 and one on the west. The RHS has carried out highway studies and is calling on the Highways Agency to choose the east option, which does not build on RHS land and would "better improve road access to Wisley", which attracts 1.2 million visitors a year.
The RHS said: "Irreplaceable historic trees that are over 100 years old could be eliminated for a short-sighted road improvement scheme, which would increase air pollution and destroy the habitats of a wide range of wildlife, including birds, moths, badgers, beetles and moles.
"Losing the natural barrier of trees on Wisley’s boundary would be visually devastating and also dramatically increase noise pollution, which would impact negatively on the enjoyment of the garden as a peaceful place to escape, relax and be inspired."
Trees that would be lost include ‘The Queen’s Tree’, planted by RHS’ patron Queen Elizabeth II to mark her silver jubilee and five trees identified as threatened and endangered in cultivation by Plant Heritage’s Threatened Plants Project. Specimens of giant redwood (Sequoiadendron giganteum) would also be at risk.
Alan Titchmarsh, RHS ambassador, says: "This potential garden grabbing plan would be another unacceptable example of this government’s poor perception of horticulture and lack of appreciation of the vital role that plants play for the environment, for the nation’s health and well-being and for the UK economy.
"Wisley is the UK’s centre of excellence for horticulture and horticultural science and helps millions of people to garden and grow plants. I’m calling on the UK’s army of 27 million gardeners to make it known that a disregard for these important trees and lack of appreciation of the national importance of this garden would not be acceptable if the short sighted and environmentally damaging option was chosen. We must stand together and protect our gardens."
Sue Biggs, RHS director general, said: "It would be criminal for this irreplaceable woodland to be lost when another viable plan would avoid cutting down these century old trees and still meet the important need to widen the A3.
"We’re currently investing over £70 million into RHS Garden Wisley in horticulture, new laboratories, learning buildings and visitor facilities, making the garden an even more important centre for science, and a better place to visit.
"The role that these trees play in mitigating against pollution, giving a home to wildlife and providing a visual and noise barrier to preserve the peace and productivity of the garden cannot, and must not, be underestimated. We are seriously concerned how the noise of the A3 without the trees would impact on our visitors, and therefore, on the future of the garden."
Widening the A3 is part of the Highways England’s plans to improve Junction 10 of the M25 as well as the A3 and its access to Wisley. The agency said traffic queues to the gardens from the A3 were unsafe at times. It is considering and has consulted on building a new access road as part of improvements to junction 10 of the M25, with a decision on its preferred route within the next month, followed by an application to the planning inspectorate, another public consultation, and potentially work starting in 2020.
It said: "Both the options we consulted on in the winter include better, safer access to Wisley gardens and we will continue to work closely with RHS Wisley as we take the project forward. We look forward to announcing the results of the consultation soon."