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.  “This increasing prioritization of creating green spaces in unexpected spots and underutilized spaces in communities is not only going to be making our communities more…