It’s not just easy to miss, but often downright hard to notice. A simple patch of greenery in a city may seem like a blip in the concrete jungle, but it’s an extremely powerful way to solve a bunch of problems at once: Studies have shown that green spaces improve urbanites’ mental health, make summers more bearable, and prevent flooding by soaking up stormwater.

When these plots are planned — as opposed to letting vacant lots grow wild, which is valuable in its own right — they become extra powerful. You may have even enjoyed one without knowing it: the “pocket garden.” Tucked into spaces accessible to pedestrians, like sidewalks, hospital grounds, and campuses, they can be engineered to turn heat-absorbing concrete into air-cooling oases packed with vegetation and seating for people to escape the metropolitan bustle.