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An empty lot in north Philadelphia, Pennsylvania

Mark Makela/The New York Times

This city fights crime with gardening

The best tool to fight crime may be a lawnmower. That’s the conclusion of a new study, which shows that sprucing up vacant lots by doing as little as picking up trash and cutting the grass curbed gun violence in poor neighborhoods in a major U.S. metropolis by nearly 30%.

“This is a really innovative study,” says Jim Sallis, a psychologist and behavioral medicine researcher at the University of California, San Diego, who was not involved with the work. It’s “a clear and convincing demonstration” that simple improvements to vacant lots help make urban neighborhoods safer, he says.

Vacant lots are abandoned property plots that often become overgrown with grass and shrubs and littered with trash and debris from illegal dumping. Across the United States, they make up about 15% of land in cities—an area about the size of Switzerland. But generally, each individual plot is no bigger than a tenth the size of a U.S. football field. Criminals exploit these neglected fields to sell and use drugs and as escape routes during police raids.

Previous work showed that new laws and treatment programs for criminals only sometimes made a difference in reducing gun violence. Charles Branas, an epidemiologist at Columbia University, wanted to try a new strategy. “We wanted to approach something that had a much deeper reach, something that would touch the very structures that we thought were driving firearm violence in the first place,” he says.

So he took aim at the dilapidated spaces that can lead to and spread violence and crime to other nearby places. Restoring vacant land was a potential solution that hadn’t been tested on a citywide scale with low-income residents, he says.

To find out whether renovating neglected lots could lower crime, Branas and his colleagues coordinated with the Pennsylvania Horticultural Society and Philadelphia Division of Housing and Community Development to enlist local contractors to clean up hundreds of the more than 44,000 vacant lots across Philadelphia, Pennsylvania. Some abandoned lots were transformed into parklike settings by clearing trash and debris, leveling the land, planting new grass and a few trees, and building a low, open fence in front of or around the space to discourage dumping and demonstrate that someone was taking care of the space. In other lots, contractors only picked up litter and mowed the existing lawn. The researchers compared this second intervention in combination with the first treatment with a third, control group of lots that stayed the same throughout the 3-year study. They also analyzed police reports and interviewed neighborhood residents during the 18 months before and after the green-up.

Compared with leaving the lots as is, transforming lots into parklike spaces or sprucing up them up with trash removal and mowing reduced overall crime by a modest amount, less than 10%. However, the effects were amplified in neighborhoods below the poverty line. There, landscaping vacant lots reduced overall crime by more than 13% and dropped gun violence by nearly 30%, the team reports today in the Proceedings of the National Academy of Sciences. Burglary and nuisance reports also plummeted in these neighborhoods by nearly 22% and 30%, respectively, thanks to the gardening.

Neighbors felt safer as well. Residents living near lots converted to parklike environments perceived less crime in their neighborhoods and reported feeling 58% less fearful of going outside than people living near unimproved lots. People who lived near renovated lots also used the spaces to relax and socialize 76% more than inhabitants near unmodified lots.

These trends themselves may reduce crime, researchers suggest. Seeing and interacting with people in your neighborhood on a recurring basis is “a powerful force” in helping people feel safe in their communities, says William Sullivan, a landscape architect at the University of Illinois in Champaign who did not participate in the work. Sallis adds that despite being small, the lots are suitable for socializing and bringing kids to play outdoors. “There’s just great benefits from being outdoors—socially, mentally, exposure to vitamin D, for example,” he says. And that means “we could expect benefits beyond the ones they documented.”

Not everyone was thrilled about the interventions. Some residents worried about gentrification and property tax increases. But Branas and colleagues did not find that the cleanups triggered gentrification, and for the most part, especially in poorer communities, the renovations seemed to be a welcome and overdue change to residents.

Branas and team designed the interventions to be cheap—only $5 per square meter in initial costs and $0.50 per square meter, or less than $255 per month per lot, in upkeep—and believe such citywide interventions can be scaled. But Sallis wants to know how. “Who would be responsible?” he asks. One possibility, he says, is that cities might acquire landscaping grants from the Department of Justice as a crime-fighting tool or health departments as a mental health promotion tool, because people feel less stressed when they feel safer.

Branas is cautiously optimistic about extending the results to other cities. “We tried to present a program here that … has a protocol to it,” he says, which other cities could adjust to fit their needs.

For Sullivan, the work shows that neighborhood landscapes matter. “Too many policymakers think landscapes are an add-on, frivolous, trivial,” he says. But research continues to demonstrate “that the way in which we treat the landscape is significant,” he says.