Gardeners are being asked to "do nothing for nature" this May by leaving their lawns to grow to help bees and other wildlife.
Conservation charity Plantlife has launched the No Mow May campaign to allow wildflowers to bloom in gardens around the UK, providing more food for pollinators.
Towards the end of the month, gardeners can enter the Every Flower Counts survey, which records the number of flowers by species and pollen count.
The charity has warned of the impact of climate change on the nation's plantlife, with spring droughts devastating the wildflower blooms.
Last year, after the driest May since 1896, the Plantlife survey saw huge drops in the number of common spring flowers in gardens. Dandelions had declined by 56 per cent compared with 2019, and daisies by 40 per cent.
Dr Trevor Dines, a botanical specialist from Plantlife, said: “Along with the browning grass, Every Flower Counts provides evidence for the first time that spring drought periods affect the timing and quantity of flower production on lawns, as early flowers wilt and summer species bloom earlier.
"With ongoing climate change, this could have important implications for delicate plant-pollinator relationships – 56 per cent less dandelion flowers could have a serious impact on early emerging bumblebees for example - and these changes will be felt across other grassland habitats such as flower-rich meadows and road verges.”
Other species saw dramatic declines last May, including the germander speewell and bird’s-foot-trefoil.
Some high-nectar producing species, such as white and red clovers, bloomed early due to the heat, so the overall 19 per cent drop in flowers was not matched by the drop in nectar.
After a very dry April this year, the best thing to do for a lawn suffering drought is to allow the remaining flowers in the soil to grow, Dr Dines said, adding that a mix of wildflowers and plants is most effective.
“If you want to have a drought-resistant lawn you want a good mix of native plants because they will often have deeper roots that go down further and can tap into scant water resources,” he said.
Plantlife has also asked councils to leave parks and road verges to go wild in May. Highways England announced in December they were working to improve soil fertility on road verges to encourage the growth of wildflowers.
Dr Kate Petty, Plantlife's road verge campaign manager, said seven out of 10 councils were now working to encourage wildflowers on verges.
Of the 3,200 gardeners who took part in last year's Every Flower Counts survey, 36 per cent said they had left their lawn unmowed for the month, up from 15 per cent in 2019 and 21 per cent said they had not mowed all year.
Participants recorded 97 different species of pollinators on their lawns, including 21 different bees and 26 butterflies and moths.
The gardens left growing all year attracted the highest number of pollinators, with an average of 3 per square metre.
Britain's 15 million gardens could also be vital in combating the loss of flora seen down the last century.
On a single day in summer, an acre of wildflowers can contain 3 million flowers, enough to produce 1kg of nectar sugar, Plantlife said.
Wildflower meadows in the UK have declined by 97 per cent since the 1930s, with an area more than 1.5 times the size of Wales now lost.
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