Further research into how gardens help cool city air temperatures may have to come from overseas or non-traditional horticultural bodies, the RHS has said.
The society's latest report Gardening Matters: Urban Gardens brings together UK and international research showing how important urban gardens are at reducing temperatures. Plants also bring down energy consumption by providing shelter and insulation, reduce the risk of flooding by absorbing rainwater and support increased biodiversity, it found.
Areas where further work was needed were identified, such as in plant physiology research into evo-transpiration and insulating buildings.
RHS science head Dr Roger Williams said: "We hope to do a bit but it is a much bigger problem than we can tackle ourselves. This puts a marker down that we want to work with others. It's difficult because of cutbacks, which is why we need to look beyond the UK and areas not traditionally related to horticulture. There might be sources of funding in well-being or mitigating the effects of climate change."
He added: "We are concerned that with current trends for building apartment blocks and houses with smaller gardens the benefits from private gardens will decrease to the detriment of people living in cities. We hope this report will highlight the need to keep green spaces for the benefit of the environment and future generations."
Research showed that urban environments were prone to heating when vegetated areas were replaced with impervious surfaces. Pavements and roads absorb more heat and reflect less than planted surfaces. This results in urban air and surface temperatures being significantly hotter than rural areas.
However, lead author Dr Tijana Blanusa added: "Gardening can contribute indirectly to carbon emissions through the use of powered tools and the manufacture and transport of horticultural goods. And the use of water in gardens is predicted to rise over the coming years."
Percentage increase in impervious surfaces in Leeds over a 33-year period