The surprising effects trees versus grass have on your mental health

Everybody knows that being around nature can make us happy, healthy, and even improve our mental well-being – but we’re human, and we’re inexplicably picky. Not all foliage is created equal when it comes to having a positive effect.

In a study published last week in JAMA Open Network, researchers at Australia’s University of Wollongong attempted to figure out what sort of green space in any given city would provide the biggest mental benefit. Would it be a giant park? A small little patch of grass with a bench? A community garden? Rooftop gardens?

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For the study, the researchers compared three types of green spaces: tree canopy (mature trees whose leaves and branches provide coverage of the ground when viewed from above), grass, and low-lying vegetation (like shrubs).

Almost 47,000 Australian adults over 45 reported whether or not they lived near these different types of green spaces, but also their self-reported mental and general health. They were surveyed twice, with the second survey six years later.

Researchers found that exposure to nature can definitely have positive mental health benefits – but it depends on the type of greenery.

Tree canopy was the best. Exposure to 30% or more total green space that included tree canopy is associated with 31% lower rates of psychological distress. The people who reported living near tree canopy reported living one mile from it.

Exposure to only low-lying ground vegetation, however, has no effect. Sorry, shrubs.

Grass wasn’t especially helpful – exposure to 30% or more of grass was associated with 71% higher odds of psychological distress. The researchers noted that the study was based on self-reported surveys that did not show the full spectrum of participants’ mental health.  They warned that “this finding not to be interpreted as evidence for removing existing grassy areas or defunding the planting of new open grassy areas.”

Yes, let’s please leave the grass alone. As poet Walt Whitman wrote in Leaves of Grass, “Do anything, but let it produce joy” – the true lesson for spending time in nature.

Meanwhile, in a related study just released, researchers have began to create a framework for how city planners and municipalities worldwide can measure the mental health benefits of nature, then merge those into plan and policies for cities and residents.

The study was led by the University of Washington and Stanford University.

“Thinking about the direct mental health benefits that nature contact provides is important to take into account when planning how to conserve nature and integrate it into our cities,” said Greg Bratman, lead author and an assistant professor at the UW School of Environmental and Forest Sciences.