More than two million flowers in urban meadows across the UK have been studied to help conservationists work out which plants best boost the prospects of pollinators, such as bees and butterflies.

A team led by Professor Graham Stone, an authority on molecular ecology of insect-plant interactions, at Edinburgh University, carried out an examination of the flowers from annual and perennial species typically grown in wildflower meadows, and associated weeds. Sixty large meadows planted in Edinburgh, Bristol, Leeds and Reading were surveyed. The project involved working closely with city parks teams and local schools, who planted and looked after each meadow.

The results demonstrate that meadows made up perennial plants, that persist for more than two years, provide more food for pollinators than those made up of annual species, that die after one year and grow again from seed. High performing plants included rough hawkbit, wild carrot, common poppy, black knapweed, corn marigold and dandelions.

Perennial meadows contain more pollen and nectar and also flower earlier in the year, meaning they are best for spring flying insects such as the queens of some bumblebee species and many wild bees, and butterflies coming out of hibernation.

The research shows that a significant contribution to nectar and pollen early in the year comes from weeds such as dandelions and buttercups, suggesting that leaving some of these to flower is likely to be important to early spring pollinators.

The research also demonstrates that at some times of the year a single flowering lime tree can produce as much nectar as a single wildflower meadow covering 300 square metres.

Lead author Damien Hicks, from the Institute of Evolutionary Biology at the University of Edinburgh, said: “If you think of a garden or park as a restaurant for pollinators, then the flower species that are planted in it determine both what is on the menu and also when it will be open. Flowers vary enormously in the amount and type of useful food that they produce, and when it is produced.

“The results show that perennial plants can produce up to 20 times as much nectar and six times as much pollen. This could be used to help design habitats that are specifically aimed at boosting the pollinator community, and crucially, this method can be applied to any vegetation type.”

Dr Maggie Keegan, Head of Policy, Scottish Wildlife Trust said: “Creating wildflower meadows in urban areas is an important part of urban conservation projects such as Edinburgh Living Landscape. We want to create nature-rich spaces that provide as high a biodiversity benefit as possible so this research is vitally important.”

“With thought we can design high quality and connected green spaces in our cities that best combine urban wildflower meadows and trees. The right mix would provide a rich source of food over a long flowering season, packaged in flowers that suit a wide range of different types of pollinators.”