Cities worldwide struggle with a mental health crisis. Depression, anxiety, and stress are among the most common problems of urban residents.
Fortunately, the researchers from the University of Hong Kong have provided an answer to a question that city planners have been asking for decades: how much green space do we actually need?
The answer may be surprising. It is not always that more green is better for green spaces and mental health balance.
Urban planners have been working based on a straightforward assumption for years: the greener, the better. Cities were investing heavily in adding as many trees and parks as possible.
However, this new study reveals that attaining a moderate level of greenness is what actually yields the greatest mental health benefit. After that point, the addition of green spaces has little effect on green spaces and mental health outcomes.
The implication of this finding is quite significant. Cities with limited budgets can now decide to invest in reaching that optimal point instead of continuously expanding.
Places with insufficient green space will know exactly how much they need to increase it. Whereas neighborhoods that enjoy a moderate level of greenness can channel their resources to other areas.
The researchers looked at both ground-level views – what you see while walking along the street – and satellite images of whole neighborhoods. In both cases, the same pattern was observed: moderate greenness was the winner for improving green spaces and mental health.
Real Benefits for Real People
What implications does this have for cities? They are now in a position to set clear targets. Planners can work out the minimum green space required to safeguard mental health. They could also pinpoint the maximum limits beyond which additional greenery would no longer yield any benefits.
Another 2025 study that used wearable fitness trackers found that making parks 10% more accessible resulted in residents taking 107 more steps per day.
The effect was most pronounced for elderly people, Black and Latino communities, and less active individuals.
This is proof that the right amount and kind of green space is what can be the solution to those who need it the most, especially in the context of green spaces and mental health.
What the Research Found
A large-scale study published in November 2025 looked at 40 years of research from cities in different parts of the world. The team reviewed 69 different studies to gain insight into the relationship between green spaces and mental health.
One of their findings is that the correlation between greenness and mental health forms an inverted U-shape. In other words, there is an optimal amount of green space – not too little, and not too much – that offers the maximum mental health benefits.
The analogy with salt in cooking works well. A little bit makes food tastier. Too much spoils the dish. Green spaces are similar to our brains in that respect, especially when considering green spaces and mental health together.
How Green Spaces Actually Work
Green spaces enhance the mental health of the people through their different features. They offer places for physical activities, through which our brain releases its mood-enhancer chemicals.
Being in nature also helps one to get rid of stress and mental fatigue. Parks and gardens provide opportunities for people to meet and interact, thus, decreasing the problem of loneliness.
However, quality is just as important as quantity. A neighborhood park that is well-maintained and where people feel safe, will give more benefits than a larger but run-down green space.
Accessibility is important too. Green spaces should be within the walking distance and easy to get in for better green spaces and mental health impact.
What Cities Can Do Now
This study offers a clear plan to city leaders. They should first assess the current levels of green space in every neighborhood. Then, find out which areas are below the optimal threshold. And lastly, they should add targeted greenery in places where it will do the greatest good.
This could be the work of turning the vacant lots into pocket parks. In a street-tree-planting campaign, pick neighborhoods that are “concrete jungles”. Make rooftop gardens on public buildings. The secret is to get that level of moderate greenness in every place, not to green up the green that’s already there to the fullest.
For instance, Hangzhou, China, a city, is already benefiting from effects of this kind of work. The green space of the city grew at the rate of 1.8% yearly because of its “Park City” policy.
People there claimed to have had a great improvement in both their physical and mental health, strongly showing the role of green spaces and mental health outcomes.
A Path Forward
Mental health problems in cities are a serious issue that keeps getting worse. The good news is that we now have scientific proof of the role of the environment in solving these problems.
Moderate amounts of accessible, well-maintained green space provide measurable mental health benefits.
This is not about converting cities into forests. It is rather a matter of strategic greening that reaches everyone. Small neighborhood parks.
Tree-lined streets. Community gardens. These additions, placed thoughtfully throughout urban areas, can make cities healthier places to live by strengthening green spaces and mental health connections.
Message to residents is straightforward: make use of the green spaces present in your neighborhood. A walk in the park, time spent in the garden, or even a tree-lined street can actually lift your spirits.
City planners, on the other hand, have a clear goal now: make every neighborhood reach that optimal level of greenness when mental health benefits are at their peak.
Karan Shukla is a college student pursuing a Bachelor’s degree in Environmental Science, with a strong focus on sustainability and climate change. He is passionate about environments issues, biodiversity and greenery and he also conducts independent studies on them. Karan aims to educate and inspire others on pressing global issues.