Fifteen years after Gardening in the Global Greenhouse, the RHS has launched Gardening in a Changing Climate, an update of the original document. The new report has been written in collaboration with researchers from the University of Sheffield and the University of Reading.
Specifically aimed at the horticulture industry, report authors including Dr Ross Cameron from the University of Sheffield recommend "greater use of locally sourced plant material to reduce energy associated with transport (and) greater use of transport hubs by industry to improve the efficiency of distribution".
The authors believe that artificial lawns, plants from arid countries and flower beds designed to cope with floods will be among future features of UK gardens as climate change kicks in. For the north of England, 2100 could be 2 degsC warmer with more winter rain, more extremes and more violent storms, meaning more robust plants are needed.
The report argues palm trees such as Chinese windmill palms; fruits such as grapes, peaches and apricots that will also help with shade; rosemary beetles; solar-powered lawnmowers; artificial lawns; New Zealand willow herb; verandas and more heavy rain showers will become prevalent.
But apples, cherries and pears will suffer from fewer chill days in winter. Drier landscapes may become easier to weed, busy Lizzies hit by downy mildew will suffer further, greenhouses and fences will have to cope with stronger winds, tulips will not bloom for as long because of warmer springs, oaks will suffer from oak processionary moths and box blight will spread in warmer weather.
Cameron says there are some positive messages for the industry. "Generally better growing conditions will aid growers, albeit having to deal with the unpredictability of more frequent droughts and flood events. There will be threats from new pests and diseases, but perhaps as a consequence a drive for 'locally-grown'. I personally think green spaces will be more highly valued by policymakers, due to their ability to help us cope with extreme weather. In terms of the domestic garden itself I think there will be some physical changes and alterations in planting style, but also a lot of impact due to changing lifestyles."
He says there will be more plant breeding for tolerance to stress and ability to flower in difficult conditions, such as "winter" pansies, repeat flowerers and smaller herbaceous perennials and trees.
There could be two trends in plant selection - tolerant stalwarts such as buddleia, berberis, and spirea; and specialist plants for specific locations such as primula cultivars for bog conditions and plants well-adapted for xeriscapes such as new cistus, helianthemum and Delosperma. In the drier south and east there could be even more emphasis on grasses and Mediterranean-style bulbs.
"In general, higher temperatures could increase the range of plant species offered by the garden industry," says Cameron. "This will be tempered by concerns over imported pests and diseases and possible invasiveness of any new taxa."
Low-energy solar or wind-generated electric powered tools could become more popular and there could be a "more relaxed attitude to the lawn" with less mowing and fertilising. The report also suggests "industrial bio-culture' of sphagnum derived products instead of peat.
Cameron says the garden industry may be boosted by people spending more times outdoors. They will use more barbecues, garden furniture, parasols, rain shelters and water harvesting, with a greater focus on the transitional nature of the patio and garden seeing a greater turnover of plant types. Ornamental plants may be more actively promoted by the landscape industry and garden centres for their functional traits - their services as well as their looks. This includes catalpas, paulownia, Fatsia and magnolia for shading, climbers on walls, pine and Picea for holding rainwater in their canopies and wildlife friendly plants.
Expert consultation on climate projections and phenology was provided by Dr Mark McCarthy (Met Office) and Professor Tim Sparks (Coventry University). The report findings will form the basis of a show garden at the new RHS Chatsworth Flower Show (7-11 June).