Snapping off his headphones, Jose Hernandez excitedly held up a treasure he’d found in the dirt. “Una cebolla,” said Jose, brushing off a white bulb.

Jose had indeed found a wild onion, along with a greater appreciation of horticulture since joining Walton High School’s inaugural class of Green Teens this year. The new program teaches students about a range of environmental topics. It’s also instilled an appreciation of the outdoors, and school in general, in kids who haven’t usually cared about either.

“It’s a new experience for me,” said Ariel Francisco, 17, pausing from his job raking topsoil. “I never worked in this stuff before.”

Stephen Ritz, a dean at the Kingsbridge Heights school, started Green Teens after he observed students’ enthusiasm for parks during an event last year. Ritz knew of environmental programs for high performing students, but none for kids needing extra attention.

That’s true of many of the students at Walton, which struggles with severe overcrowding, violence, and low graduation rates. (Walton will receive one of the second largest allocations of dropout prevention funds in the Bronx next year.)

Ritz drafted a curriculum for the program with help from the Friends of Van Cortlandt Park, an advocacy group, and the Green Teens debuted last winter. Interested students had to interview for a slot. “Some of them came dressed up in shirts and ties,” said Mark Conley, a Walton teacher running the program with Ritz.

The group consists of 18 mostly male students who spend a portion of their day learning about ecology, horticulture and environmental science. They put those studies to use after-school and on the weekends while beautifying local parks, planting vegetables for a soup kitchen program, and examining Van Cortlandt’s flora and fauna.

“They are giving up their own free time to do this,” Ritz said.

Students are moving up from the basics — figuring out what weeds and poison ivy look like— to testing water quality and conducting advocacy. Junior Tavarez, 16, was initially bored by the work.

“I thought all we were going to do was dig in the dirt,” he said. “But I got interested when we started learning science.”

Kristy Figueroa, 18, tested her fledgling advocacy skills at a recent parks event with officials. “We are learning in a different way,” she said.

A major part of that difference is being away from the thousands of other students jammed into Walton. Kristy says the overcrowding is stressful and makes it hard for her to pay attention. Jose is burdened by the school’s gang problems. “It’s a tough environment,” he said.

Many Green Teens say they get along better outside. “In school, it’s just about the way you dress,” Jose said. “Here we interact about other things.”

The time also seems to allow students to cultivate more meaningful relationships with their teachers, and the school itself. Green Teens will be planting 150 trees and bushes outside the school before summer break. “It’s all messed up now,” said Ariel, noting that cars tend to drive over the grass.

Walton’s administration has been supportive of the program, but it isn’t always easy to get space for them. “It’s not the safest environment for storing things,” said Conley, noting that another student ripped out a sapling planted in his classroom.

Despite the bumps, Green Teens has far surpassed Ritz’ expectations. Its participants have maintained a 90 percent attendance rate, he said, compared to Walton’s average of 75 percent last year. To remain in the program, students must stay in good academic standing.

“I’m shocked,” Ritz said about their success. “You usually can’t get these kids to school, and look at all they’ve done.”

Ritz says that others are noticing the program’s merits, and Discovery High School, a small school housed within Walton, will probably start a satellite Green Teens.

Ritz would love to expand the initiative at Walton but is limited by how much staff time can be devoted to the effort.

“It’s a tremendous amount of organizing work,” said Ritz who is an energetic cheerleader for the Green Teens.

Jose is looking forward to going to a vocational school next year, and while not looking to make a career out of it, hopes to keep doing horticulture as a hobby.

“I wish I had this program when I was a freshman,” he said.