Christopher Coombs, executive chef of Dorchester's dbar, is going green from the top down. His rooftop garden, overlooking Dorchester Avenue on one end and the restaurant's patio on the other, is home to 23 different types of tomatoes growing on more than 65 plants. And Coombs swears that from Paris to Virginia, his homegrown tomatoes are the best he's had in his life.

"Flavor is what I grow up on that roof," Coombs said.

Tomatoes dominate the rooftop this month because they're in season, and Coombs said he will harvest more tomatoes than he can use in the coming weeks. So he has entered into an old-fashioned trade agreement with his meat purveyor, who will soon be selling Coombs's heirloom tomatoes at his shop in Newton.

Through trial and error, Coombs learns what thrives and what dies in the container gardens. Large fruits and vegetables like watermelon and squash are difficult to grow because of limited space, but peas and carrots do well on the rooftop, as do the extensive herb gardens which house everything from thyme to nasturtiums. From June to October, Coombs said he cooks solely with fresh herbs from the roof, saving the restaurant up to $400 a week.

Aside from saving dollars, dbar's rooftop garden saves energy and reduces the restaurant's carbon footprint. Last year, 23 percent of dbar's produce came from the rooftop and Coombs said he is shooting for 25 percent this year.

Coombs compares his harvest to raising a child and he encourages his staff to do the same. They don't burn and they don't waste, Coombs said. "That doesn't happen here ever because we have a deep appreciation for the vegetables and fruits and how much work we put into it."

"This is just the beginning," Coombs said of dbar's garden, noting that "no one else is doing this." Recently, he started working with Jim Hunt, Boston's chief of environmental and energy services, to learn ways to expand the restaurant's energy efficiency through its green roof.

"He and I want to work together so we can inspire more chefs and more restaurateurs to make this a common practice," Coombs said. "We could really save a lot of energy - think about the amount of rooftop space there is in the city."

As part of Mayor Thomas Menino's Grow Boston Greener campaign, the city is also looking to expand green roof coverage on municipal buildings. A $50,000 grant from the Department of Environmental Protection will fund a study to examine the benefits of green roofs and discern which already-existing city buildings are good candidates for green roof installations.

Hunt said dbar's "impromptu" green roof, born out of a chef's desire to grow local produce, has numerous environmental benefits. Green roofs serve to insulate buildings, reducing energy consumption and alleviating some of the "urban heat island effect" that makes inner-city neighborhoods more than 10 degrees hotter than other areas. The abundance of blacktop sidewalks, roads and rooftops in the city attract and trap heat, but rooftop vegetation cools as it absorbs the sunlight.

Lower temperatures also help alleviate public health threats such as heat stress, asthma and other respiratory problems, Hunt said. As natural drainage systems, green roofs lessen storm water pollution and locally grown produce cuts fuel consumption and costs.

In a country where the average piece of produce travels 2,000 miles before it reaches the table, Hunt said green restaurants like dbar have a lot to offer the neighborhood. Hunt expects that "we will continue to see an increase in our green restaurants," which means "more sustainable food, reduced costs and a healthy, locally grown product that's more sustainable."

Coombs admits that the green scene has become pretty "hip" this year, but it's something he personally enjoys as a chef and as a member of the community working toward sustainability.

"I do it because it's good for the environment, good for the restaurant, good for profitability, good for everything," he said.