Why untidy gardens make the best habitat for wildlife

People who want to turn their gardens into wildlife refuges should relax and let the grass grow tall, the flowers turn to seed and the hedges, shrubs and trees expand skywards.

A detailed study of biodiversity in town and city gardens has found that they offer a vital refuge for animals and plants – provided that those responsible for their upkeep are not too fastidious as gardeners.

It has also found that many of the preconceptions about wildlife gardening are not true. Small gardens are just as good as big gardens at attracting wildlife, suburban gardens are not always better than city gardens and non-native plants are not always harmful to native insects and birds.

Britain's 16 million gardens are a haven for hundreds of species of animals and plants that would find it impossible to survive on intensively farmed land, said Ken Thompson of Sheffield University.

"Gardens are amazingly diverse even compared to natural habitats that are good for wildlife. Gardens are more interesting on a small scale because they are so variable. All the wildlife responds to these variables," Dr Thompson said.

"Compared with an equivalent area of modern intensive farming, gardens are much, much better in terms of everything you measure, whether it is spiders, bugs or birds," he said.

"It sounds heretical, but from a biodiversity perspective most farmland would be improved by having a housing estate built on it," he told the British Science Festival.

Dr Thompson was involved in the first detailed study of the wildlife inhabiting British gardens when he and his colleagues surveyed 61 gardens in Sheffield between 1999 and 2002. They found an "astonishingly diverse" array of flora and fauna.

They also identified a range of simple measures that improved a garden's habitability for wildlife. "The top thing is to grow more big shrubs, trees and hedges," Dr Thompson said.

"These massively increase the volume of vegetation in your garden and a lot of vegetation means a lot of places to live and a lot of stuff to eat," he said.

"Don't be too tidy: don't be in a hurry to clear up everything when the garden stops flowering. Just leave a bit of stuff lying around.

"There's a mistaken belief that wildlife gardening is something special, something different, something odd and that a wildlife garden needs to be untidy, messy and not something you'd be proud of, but that's not true," Dr Thompson said.

The best gardens for wildlife needn't cost lots of money, and many of the "wildlife" products sold in garden centres are unnecessary, he said.

"Decking is a disaster. One of the findings of the Sheffield study was the very clear relationship between hard surfaces of any sort and less wildlife. It doesn't matter what it is – as long as it's hard, it's bad," he added.

How to get a more natural garden

*Plant large shrubs and let them grow big. Shrubs and trees produce more vegetation where wildlife can live and eat.

*Allow at least some flowers to turn to seed and the lawn to grow tall. Don't be in a hurry to clear up fallen leaves.

*Create a pond for insects, frogs and toads. Think before stocking it with fish which will eat insect eggs and larvae.

*Don't illuminate your garden at night with bright lights. This will disturb many nocturnal creatures, such as moths.

*Create a compost heap – they are miniature nature reserves in themselves. Compost also enriches the soil.