The findings, which are the first from the charity's four-year Plants for Bugs research project, are published in the Journal of Applied Ecology. They suggest that gardeners wishing to encourage and support pollinators should plant a mix of flowers from a wide range of geographical regions.
While there should be an emphasis on plants native to the UK and the Northern Hemisphere, as more pollinators from a range of pollinator groups visited these plants, plants from the Southern Hemisphere such Lobelia tupa and Verbena bonariensis can play an important role. By tending to flower later than native and Northern Hemisphere varieties, Southern Hemisphere plants provide much needed nectar and pollen long after other plants have gone to seed.
RHS scientists found that regardless of the origin of the plant (native or non-native), the more flowering plants a garden can offer throughout the year, the greater number of bees, hoverflies and other pollinating insects that will visit.
Speaking about the study, RHS lead researchers Dr Andrew Salisbury and Helen Bostock said: "The UK's 1500 species of pollinator are thought to be under increasing pressure due to the loss of habitat and food sources. As more traditional habitats have been reduced the role of gardens as havens for pollinators and other wildlife is growing in importance. That said, up until now the role native and non-native plants play in sustaining wildlife in gardens has been unclear and confusing."
"Now, for the first time, gardeners can access robust, evidence-based information on the most effective planting strategy they can adopt if they wish to attract and support pollinators. These findings will help gardeners to confidently pack their borders, window boxes and allotments with flowers without getting hung up on the idea that they are somehow doing the 'wrong thing' if the plants are not all UK natives."
The findings of the first Plants for Bugs paper could have far-reaching implications, not just for gardeners, but for any organisation involved in ornamental plantings, including local authorities, who have a responsibility for parks, and the landscape sector.
Helen Bostock added: "Organisations that have a responsibility for green spaces, regardless of their size or location, will now be able to draw on conclusive evidence to help guide them as they work to support our pollinators."
The publication of the complete results from the four-year Plants for Bugs study will be released at staged intervals over the coming years. During that period different aspects of the research will be revealed.
Subsequent RHS Plants for Bugs papers will focus on terrestrial arthropods (above-ground invertebrates) such as beetles.