Nick Carne
Mowing urban lawns less often or less severely increases biodiversity, saves money and reduces pests, according to research from the British Ecological Society.
A meta-analysis of data from North America and Europe found strong evidence, the researchers say, that greater mowing intensity at home, in parks and on roundabouts and road verges has negative effects, particularly on invertebrate and plant diversity. Pest species thrive, however.
“Even a modest reduction in lawn mowing frequency can bring a host of environmental benefits: increased pollinators, increased plant diversity and reduced greenhouse gas emissions,” says Chris Watson from the University of Quebec at Trois-Rivières, Canada, lead author of a paper in the Journal of Applied Ecology.
“At the same time, a longer, healthier lawn makes it more resistant to pests, weeds, and drought events.”
The reason, Watson says, is that regular mowing favours grasses, which grow from the base of the plant, and low growing species such as dandelion and clover. Other species that have their growing tips or flowering stems regularly removed by mowing can’t compete. {%recommended 6627%}
“These findings support a lot of research done by the turfgrass industry that shows that the more disturbance a lawn gets, the higher the likelihood of pest and weed invasion,” he adds.
For their meta-analysis, the researchers identified 14 studies undertaken in urban areas between 2004 and 2019 that measured mowing intensity (either height or frequency) as an experimental factor. They also included three unpublished studies of their own.
A separate case study was used to estimate the economic costs of high-intensity lawn management – which are known to be considerable.
Previous studies have shown, for example, that the cost of allergies to ragweed, which is common in North America and Europe, is around CAD$155 million per year in Quebec and €133 million a year in Austria and Bavaria.
As it has a more rapid reproduction than other species, the researchers say, ragweed is able to colonise disturbances caused by intense mowing.
You can also save money more directly. In their case study, Watson and colleagues analysed mowing contractor data from the city of Trois-Rivières. They estimated a 36% reduction in public maintenance costs when mowing frequency was reduced from 15 to 10 times per year in high use lawn areas and from three times to once a year in low use areas.
Watson acknowledges that people worry that leaving grass long attracts ticks and rodents but says there is little evidence to support this.
“The presence of ticks are more strongly related to host populations, like deer, than type of vegetation,” he says. “With respect to small mammals, some species prefer longer grass, whereas others do not.”
The plan now is to expand the research and begin applying the findings to improve lawns.
