Compelled by civic duty, Addie Cooke decided she had to fix the problem. The pink flowers on the young magnolia tree outside her home in
Fort Stanton were blooming on only one side.

“Don’t be jealous,’’ the 82-year-old whispered to it sweetly. “Just because I pruned one side of you doesn’t mean I don’t like the other side of you.”

The dulcet affirmation delivered by Cooke isn’t just some quirk for her home garden. Cooke is a tree keeper, entrusted to watch and water — and maybe talk — to one of thousands of new trees planted across the District.

The arboreal army, with more than 1,000 volunteers, is the first line of defense in a city program to obscure the District’s skies with tree tops. And the dead of summer is the biggest battle season.

The air is thick, and the soil is dry. Fragile young trees need water, lest they perish, which would suit some neighbors just fine. A few houses down on 18th Street SE, Elizabeth Miles fumed about the tree planting.

“The last time I had a tree, the roots got all in my water line ,” Miles, 72, said. “Now some man came and put up a new tree. I don’t want it! I tried calling tree-one-one, I mean 3-1-1, and they couldn’t do anything.”

Cooke, who has loved nature since she was a little girl, tried to explain the worth of trees — their aesthetic beauty and how they help boost property values — to neighbors. She talked to her neighbors as sweetly as she would to Marie. Yes, the tree has a name.

“They think I’m a little weird,” said Cooke, laughing.

Tree cover has recently emerged as not just an environmental indicator but an economic one, with poorer places usually having less shade. Citing the many benefits of trees, the District is aiming to have 40 percent of the city covered in a tree canopy by 2035.

The goal has led to a blitz of saplings seen throughout the city. About $1.6 million in mostly federal funding was spent on planting more than 7,000 trees last year. Efforts were concentrated east of the Anacostia River and other neighborhoods where there isn’t much shade.

Planters haven’t always been welcomed, said John P. Thomas, the city’s supervisory arborist. Neighbors are concerned that trees will mean leaves to rake and bird droppings to wipe off cars, or a shadowy area perfect for drug deals.

“We’ve been yelled at and told to get off the property, but we only use city property,’’ Thomas said. “Some people have called their councilman. Some people have said they are bringing out a shotgun. We say, ‘We’re just planting trees.’ ”

Three years ago, the city created the adoption program to improve man-nature relations. It was cheap. The alternative was contracting a company to bring out a truck and water every new tree, driving up the project’s costs and its carbon footprint.

So city officials advertised the Canopy Keeper program on billboards outside liquor stores. They hired youths to fan out across neighborhoods with young trees, wrapping on cards that say “adopt me” and bar codes that can be scanned with a smartphone for information.

They spoke about the program at neighborhood meetings, which is where Cooke first heard about it. Still, Thomas said, they struggle to find people to adopt trees.

When it came time to sign up, Cooke said, she was the only person in her Southeast neighborhood to show interest.

Cooke still remembers how beautiful the District was when she first visited her aunt in Southeast in the 1940s.

“So rural,” Cooke said, “with trees everywhere.”

By the time Cooke became president of the neighborhood’s civic association in the 1980s, Fort Stanton was a crime-ridden world of low-slung brick houses with scattered oak trees planted in nearby swales.

Cooke planted hydrangea and chrysanthemums in her front yard. She helped start a community garden for seniors. Through it all, she insisted she knew nothing about gardening. In the olden days, her neighbors, who grew up in the country, mocked her for using a tablespoon to dig holes to plant tulips.

“You think the tulips are really going to grow?” she recalled them saying. “I told them God will make them grow. And they’ve come up every season.”

Now, her neighbors are the ones who don’t really understand gardening. Other communities have witnessed similar phenomena.

After trees were planted in Carol Casperson’s Fairlawn neighborhood in Southeast, a neighbor started spraying weed killer around the branches. He had a campaign of his own: to remove trees from near his property.

But when the tree stopped growing, the city just planted another. The neighbor gave up.

“Another person put six tacks in two trees to promote an event,’’ Casperson said. “Six tacks? Don’t they understand this is a living thing?”

Still, Casperson has said she thinks her neighborhood is “becoming convinced that the trees are good things.”

It’s easy to tell the new trees. Their trunks are smaller than a young child’s waistline, enveloped in a tub or a green bag for containing water. That’s where the tree keepers deposit water once a week, maybe twice if it’s especially dry.

“I just love my tree,’’ said Cooke, who is retired.

Last year, she lost her position as president of the civic association. She recently had to stop planting vegetables at the community garden because her back couldn’t withstand all the bending and pulling. So she delights in being able to turn on a faucet, drag out her hose and perform a public service, by encouraging Marie the Magnolia to bloom.