Scientists says that new research confirms that the lawn can be a significant source of the greenhouse gases that contribute to global warming.

Grass lawns soak up carbon dioxide, which is stored in the soil after the cut grass rots and so, like trees, they are considered good for the planet. But Dr Chuanhui Gu of Appalachian State University in the US says that once the energy expended by mowing, fertiliser use and watering are taken into account, lawns actually produce more greenhouse gases than they soak up.

In a paper for the Journal of Environmental Management, he and his co-authors said they had found that a hectare of lawn in Nashville, Tennessee, produced greenhouse gases equivalent to 697 to 2,443kg of carbon dioxide a year. The higher figure is equivalent to a flight more than halfway around the world.

Dr Gu said the findings would vary based on the local climate, but the general message would apply to most areas. Nashville gets about the same amount of rain as Glasgow and temperatures range from 30C in summer to below freezing in winter.

“Climate change emissions from urban lawns and gardens are often kind of neglected by people, even scientists,” he said. “We found that the urban turf grass system actually contributes to global warming. It’s a lot. It’s about two-thirds of the carbon emissions from agricultural fields of the same area.” This contradicts previous beliefs that urban lawns generally absorb more carbon dioxide than they produce and are therefore good for the planet.

 “We had to find a balance between aesthetic concerns and environmental concerns,” Dr Gu said. “On the one hand, we want to reduce fertiliser use, but on the other hand people want to have a nice, green, beautiful lawn in their garden.”

His team developed a maintenance plan that he said typically reduced the emissions by up to 70 per cent, while still producing a pleasant effect. He said mowing should be done about half as frequently – perhaps once a fortnight instead of once a week – with watering kept to a minimum.

And fertiliser, which produces nitrous oxide, a greenhouse gas about 300 times more potent than carbon dioxide and uses a lot of energy to produce, should be used sparingly - ideally only when the grass is newly planted. Instead, grass cuttings should be left on the lawn as a natural alternative.

“Clipping recycling is a very good way to save the environment and also potentially save people money. It’s a win-win situation,” Dr Gu said. “Grass clippings are a perfect nutrient source for turf grass. It’s actually better than fertiliser.”

Guy Barter, chief horticultural adviser to the Royal Horticultural Society, backed the general approach. Mowing less often was a “good idea” and leaving cuttings on the lawn was also sensible, although he suggested using a mulching mower that chops up the leaves so they can sink down into the grass.