Householders should receive a council tax discount if they garden sustainably, researchers have said.
Artificial grass and pesticides should also be banned to help protect the environment, according to a study by the University of Sheffield.
Professor Ross Cameron said gardens must be “full of plants to be beneficial to the local environment”.
The government is aiming for everyone to be able to access green space within a 15-minute walk from their home.
Some cities may have lost half of their green garden space over the past 20 years, with homeowners paving over areas for driveways and patios or replacing it with fake grass, the researchers said.
Prof Cameron said this leads to rising urban temperatures, because plants help cool the air around them.
“Gardens account for a third of all our urban areas and are vital spaces in terms of keeping our buildings and city environments cool in summer, absorbing rain to avoid flash flooding and providing an important refuge for wildlife,” he said.
“Many residents use artificial grass that kills much of the soil life underneath it, and when real plants are present, we wrongly assume we need to hit them with a cocktail of chemicals to keep them alive and free of pests.”
The study, published in the journal Urban Forestry and Urban Greening, calls for policymakers to introduce incentives to make sure gardens are well planted, such as money off bills for householders and financial rewards for people who plant trees.
