Pearson is to present evidence from scientists engaged in botanical research at Kew Gardens suggesting that rising temperatures are sharply altering the growing patterns of many British plants.
The worst effects, he believes, will be felt by British gardeners with their fondness for luxuriant and thirsty plants such as roses and wisterias.
“The UK’s climate is changing and this is having a big impact on our gardens as well as our natural ecosystems,” Pearson said.
“The growing season for plants is now a month longer than it was 100 years ago, and many of the impacts from climate change will have significant effects on how we manage our gardens in the future.”
Long term, some of the most traditional English garden plants may become impossible to grow in southern England, including ferns, rhododendrons, poppies and rhubarb.
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Gardeners are also being advised to avoid cutting their lawns too short to help the grass to survive, and to plant lavenders, marigolds, cistus, salvias and even cacti.
It rained less in London last year than it did in such sunny hotspots as Tunis and Jerusalem, and this year the southeast has been hit by drought and water restrictions.
Kew has established a dry garden to promote water conservation, and next year it is opening a new Mediterranean garden focused on gardening with minimal water. Growers in Kent are cultivating walnuts, usually a scenic feature of the south of France.
At Winterbourne Botanic Gardens, the experimental climate change site run by Birmingham University, traditional English blooms are being replaced by alternatives such as agaves, the tough succulents from the deserts of California and Mexico.
Alison Darby, the Winterbourne curator, said she was also testing heat-tolerant alternatives to grass such as camomile and thyme.