THEY are derided as common weeds, their only fate to be torn up by the roots whenever they poke through the carefully cultivated soil of a gardener's flower bed.

But now experts say green-fingered flower enthusiasts should lay down their trowels when they spot a dandelion's bright yellow petals, as the plant may just be key to reviving the struggling fortunes of the nations bumblebees.

Bumblebee numbers have been on decline for more than a decade, with two species going extinct in the UK in recent years.

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Yet scientists say that the best way to help the much-loved insects revive is to plant meadows of common perennial plants that most horticulturalists would normally consign to the compost heap.

A team from the University of Edinburgh carried out a study of more than two million flowers typically grown in wildflower meadows by surveying sixty large plots in Edinburgh, Bristol, Leeds and Reading.

They found that the areas containing wild flowers such as rough hawkbit, wild carrot, common poppy, black knapweed and corn marigold 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, as well as butterflies coming out of hibernation.

Furthermore, their research also shows that a significant contribution to nectar and pollen early in the year comes from weeds such as dandelions and buttercups, which means leaving some of these to flower is likely to be important to early spring bees.

Bumblebees are great pollinators, and play a key role in producing much of the food that we eat. Through the pollination of many commercial crops such as tomatoes, peas, apples and strawberries, insects are estimated to contribute over £400 million to the economy.

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 at the Scottish Wildlife Trust, added: “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.”

David Jamieson, Head of Parks, Greenspace and Cemeteries, City of Edinburgh Council said: "We welcome these research results as they clearly show how as a local authority we can significantly improve the biodiversity where most people live, work and play simply by changing the way we maintain our urban parks and gardens. It’s a win-win for both wildlife and humans."

The research, Food for pollinators: quantifying the nectar and pollen resources of urban flower meadows, is published in the open access Journal