Nectar production was measured in almost 200 species of plant by extracting nectar from more than 3,000 individual flowers.
Mr Tew, who is studying for a PhD in ecology, said: “We found the nectar supply in urban landscapes is more diverse, in other words – (it) comes from more plant species than in farmland and nature reserves, and this urban nectar supply is critically underpinned by private gardens.”
“Gardens are so important because they produce the most nectar per unit area of land and they cover the largest area of land in the cities we studied.”
The extraction process used a fine glass tube, with the sugar concentration of the nectar then quantified with a refractometer – a device that measures how much light refracts when passing through a solution.
In total, 29% of the land in urban areas comprised of domestic gardens – six times the area of parks and 40 times the area of allotments.
Mr Tew said it was vital for new housing developments to include gardens and called on gardeners to ensure their spaces are “as good as possible” for pollinators.
He suggested planting nectar-rich flowers, ensuring there is always something in flower from early spring to late autumn and mowing the lawn less often to let dandelions, clovers, daisies and other plants grow.
Gardeners should also avoid spraying pesticides as these can harm pollinators, and avoid covering their gardens in paving, decking or artificial turf, he said.
Dr Stephanie Bird, an insect scientist at the Royal Horticultural Society, said: “This research highlights the importance of gardens in supporting our pollinating insects and how gardeners can have a positive impact through their planting decisions. Gardens should not be seen in isolation – instead they are a network of resources offering valuable habitats and provisions when maintained with pollinators in mind.”
The paper, Quantifying nectar production by flowering plants in urban and rural landscapes, is published in the Journal of Ecology.