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Vacant city lots with overgrown weeds and trash are ugly, for sure, but research shows there is yet another reason to clean them up and make them green: It lifts residents’ moods and feelings of self-worth, according to a new study.

The study, published last month in the Journal of the American Medical Association, found that when empty spaces in Philadelphia were improved – at a cost of between $1,000 to $3,000 per lot – there was a significant jump in overall mental health for nearby residents, particularly for those struggling economically.

“There’s a growing body of evidence that green space can have an impact on mental health, and that’s particularly important for people living in poorer neighborhoods,” said Eugenia South, an assistant professor of emergency medicine at the Perelman School of Medicine at the University of Pennsylvania and one of the authors of the study.

The harm of a blighted neighborhood has been well-documented, with studies showing that it’s bad for our health. Even walking by overgrown, trashy patches can quicken heart rate and signs of stress.

Research also shows that when a once-neglected lot is cleaned and greened, it becomes a less appealing place for crime, causing a drop in gun violence and vandalism.

This latest study shows that if cities are willing to remove trash, plant trees and grass and put up a short wooden fence, it is likely to make people feel less depressed and worthless.

When studying empty lots, researchers have plenty to choose from: About 15 percent of urban land lays vacant, according to the Brookings Institution.

In Philadelphia alone, there are more than 43,000 vacant lots. Researchers examined 541 of them, randomly chosen across the city, and divided them into three groups.

One group got the full treatment: trash removal, land grading, planting new grass and trees and installing a low wooden fence around the perimeter. A second group got limited beautifying: trash cleanup and some grass mowing. The third control group got nothing.

The study surveyed 342 randomly chosen residents living near the lots. They approached the residents 18 months before and after the cleanup, asking how often they felt nervous, hopeless, restless, depressed and worthless.

Neither the survey team nor the residents knew that the survey was about vacant lots; they were told only that the study was about improving understanding of urban health.

Results showed that when a patch got an investment of between $1,000 and $3,000 – the full treatment – residents living nearby who had incomes below the poverty line said they felt happier. Specifically, their feelings of depression decreased by more than 68 percent.

For those living in neighborhoods where residents’ income was above the poverty line, feelings of depression decreased by more than 41 percent after vacant lots were greened.

People living near lots that had only trash removed, but were not greened, showed no significant improvement to their mental health. This is probably because no additional green space was created, the researchers argue.

South said the findings show that “there’s something that’s actually important about the green space,” and that the mental health benefits stem not just from trash removal, which signals increased investment in a particular neighborhood.

The enhancements to the lots in the study were performed by the Pennsylvania Horticultural Society, which since 2004 has been “cleaning and greening” vacant areas across Philadelphia, helping to create thousands of parks and community gardens.

Researchers stressed that this is a low-cost way for cities to help improve residents mental health – it costs an average of $1,600 to green a vacant lot, plus $180 per year for maintenance – and is also a way to promote health and safety.

“It’s a relatively low-cost intervention … and it’s a pretty simple intervention,” South said. “It’s very simple to replicate. It’s not complicated and could be easy for a city that hasn’t done this.”

And because it is affordable for cities, South hopes that vacant-lot greening would be an attractive measure for policymakers looking to tackle urban blight in cities everywhere.

“I think this paper gives policymakers who are interested [in greening urban spaces] more evidence and backing to put more resources into this,” she said.

One of the most important takeaways from the study, South said, is that “we can make a dent on health disparity.”

“We know that health outcomes are different in different neighborhoods,” she said, and by making changes to the physical environment that lead to improvements in mental health, “we can make an impact on the entrenched health problems that we have.”

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