Michael Ring usually doesn't have a green thumb. In fact, the fifth-grader's first foray into gardening was just last week, and it occurred eight stories above City Hall Plaza.
Michael and his science classmates from the Warren-Prescott School in Charlestown installed 25 planters as part of a growing green-roof project atop City Hall. The 1 1/2-hour outing was a small functional improvement for City Hall, and a hands-on education for the 25 fifth-graders.
"We learned that when it rains, chemicals wash off the building into the Boston Harbor," Michael said.
"I never knew it was like that before. I thought water was OK running off buildings, and now I learned that it's not, so we need to make planters to hold the water."
Ring and his classmates are the latest group of students to work with Plants Across Communities, a nonprofit group founded in 2005 to educate Boston public school students about environmental sciences and green building by installing planters at their schools and City Hall.
Cofounders Jeff Licht and Bruce Schwoegler have so far worked on projects with students from the Josiah Quincy School in Chinatown, the Curtis Guild School in East Boston, and two groups of students from Warren-Prescott.
"Our job is to try to use a variety of methods and materials to teach children science, especially children who are underserved in terms of science education in school," Licht said.
"We've found that students take a lot away from working on the green roof at City Hall, and from green projects in schoolyards at their schools."
City Hall officials hope the growing green roof on their building will be an education to more than just fifth-graders.
"When we talk to developers about green building as a part of the mayor's commitment to sustainability, green roofs are one thing that we recommend," said Bryan Glascock, director of the city's environment department.
New developments in the city of more than 50,000 square feet must be certifiable under the Leadership in Energy and Environmental Design rating system, meaning they must meet a standard of environmental friendliness calculated by amassing points for building techniques, such as using recycled materials, conserving energy, or installing a green roof.
There are already examples of innovative green-roof projects around the city. The park in Post Office Square is a green roof above an underground parking garage; the Seaport Hotel in South Boston features a green roof, as does a new utilities building at Northeastern University.
Licht stressed that the modest garden atop City Hall does more than soften the building's stark appearance.
One hundred of the 15-inch-square plant boxes are scattered over two floors, and Licht eventually hopes to install as many as 600 planters at City Hall and expand the program to more elementary schools in Boston.
The plants help reduce the building's cooling costs by protecting concrete from the scorching summer sun. They also keep water from overloading the sewer system during heavy rain.
Already, the boxes have drawn unexpected new residents to City Hall Plaza.
Glascock brushed his hands across a tuft of sedum plants last Thursday, revealing a pack of grasshoppers that had somehow found their way to the island of greenery in a sea of inhospitable concrete.
The insects have, in turn, attracted birds, such as warblers, that could be heard singing from nearby picnic benches.
"Once you get a little bit of an ecosystem, birds will come in," he said. "You get a little more diversity downtown -- not just pigeons."
Tina Champagne, a science teacher at Warren-Prescott, said she hopes to continue the project at both City Hall and the Warren-Prescott's schoolyard.
"What's really neat about the boxes is it really is cross-curricular," she said.
She plans to return to City Hall with more students in the fall, and to use the planters that students have installed around the school as a teaching tool.
"There's a math component that's really easy to implement," she said. "There's a science piece that I see extending well into next year."