WASHINGTON, D.C. — Volunteers in the Mount Pleasant neighborhood of Washington, D.C., installed a pocket garden of native plants on a street median to support pollinators and help cool an urban heat island. The plot is one of more than 30 neighborhood tree boxes known as pocket gardens across the city, part of a broader trend of native-plant plantings in urban areas.

The tiny plot contains golden alexander, phlox, and columbine, among other plants that bloom throughout the year. John Burnham, a retired federal worker and volunteer gardener in Mount Pleasant, contributed an additional species to the bed. Stella Tarnay, executive director of Capital Nature, a local nonprofit assisting in the neighborhood effort, said the plant's spreading habit is part of its appeal for gardeners hoping to attract bees, butterflies, and other beneficial insects.

"I brought some mountain mint, which was the Plant of the Year last year for native plants," Burnham said.

"Once you plant it, it's going to spread. But it's one of the best plants that you can plant in your yard if you want to support pollinators," Tarnay said.

The area where the garden was installed is an urban heat island, a zone that gets hotter than surrounding areas because of heat-absorbing materials like asphalt and concrete. Adding greenery can lower temperatures in such locations. Tarnay said the benefits of native plantings extend below the surface as well.

"When you put in the native plants, they create these wonderful little root systems that aerate the soil. They attract insects, beetles, worms, not only the charismatic pollinators. And they also bury into the earth," she said.

Tarnay described the transformation of a strip of pavement that most pedestrians cross without a second thought. "This is basically just a hop-over median on the way to the liquor store for many people," she said. "But in this little box, there's so much life that's starting to go on."

Kate Brown, an environmental historian at MIT and the author of "Tiny Gardens Everywhere," said small green spaces can play an outsized ecological role in built environments. "Mostly because these tiny, green spaces dotted throughout an urban and suburban territory offer refuge for all kinds of birds and animals and insects that they don't get in the countryside, which is continually being bombed by things like insecticides and pesticides," Brown said.

For Burnham, the motivation is also a neighborhood one. "Can't we create a little bit of joy in our own neighborhood here? That's the idea," he said.