Looking at the skinny elm sapling reaching for the sky in his backyard, James Bryant said that he hopes he lives long enough to be able to sit under its canopy and read a book in summer.

Bryant’s neighborhood in Charlottesville has the dubious distinction of being the hottest in town. Walking the blocks around the intersection of 10th and Page streets, it’s easy to see why—trees that could offer some shady relief from the broiling summer sun are few and far between.

“We couldn’t sit out until late evening to have cookouts because it was so hot,” he said.

Like many communities across the Chesapeake Bay watershed, Charlottesville and its nonprofit partners are trying to change that. Bryant has a new crape myrtle in his tiny front yard and a pair of nascent shade trees out back, courtesy of volunteers with the Charlottesville Area Tree Stewards. This fall, the city’s Tree Commission is going door to door in the neighborhood looking for at least 20 more homeowners willing to have...