Mindy Maslin, quite literally, is rooted in her community.

Known as "the tree lady from PHS," Maslin began working for the Pennsylvania Horticultural Society 20 years ago, when - it's crazy to imagine now - she didn't know the difference between an oak and a maple.

But in 1993, she had an idea, one that played to her strengths as a community organizer, political and environmental activist, and social worker. Inspired by a fledgling group in Chicago called TreeKeepers, Maslin founded Tree Tenders, to help Philadelphia take care of its street trees.

PHS would train volunteers all over the city - initially to maintain the trees and eventually to plant new ones. It would also provide the trees, tools, and expertise.

Who could have imagined that by 2010, 3,600 Tree Tenders in 220 neighborhood groups would have planted 15,000 street trees in Philadelphia? Or that recently, 85 more groups would pop up in Bucks, Chester, Delaware, and Montgomery Counties and plant 5,000 more?

Tree Tenders also can be found in Pittsburgh, Harrisburg, and a dozen more metropolitan areas around the state, as well as in Moorestown and in Delaware. Flint, Mich., and other cities have expressed an interest in starting programs, too.

"Mindy is amazing," says Drew Becher, PHS president since June. "Her gift to the city is going to be one that, over the years, will only get better. That's the beauty of trees."

In 2007, Becher helped found MillionTreesNYC, which has planted more than 400,000 trees in New York City to date. He says he hopes to "rapidly expand" Tree Tenders outside Philadelphia.

Soon enough, the volunteer tree-planters will be busier than ever. In 2011, PHS plans to launch TreeVitalize One Million, with the goal of planting a million trees in Philadelphia, South Jersey, Delaware, and the rest of Pennsylvania by 2026.

"This has been an amazing journey," says Maslin, 50, of the city's Blue Bell Hill neighborhood, an unassuming tree geek who inspires intense loyalty.

"I'd walk miles for Mindy," says Marilou Regan, a Tree Tender in Springfield Township, Delaware County, whose group got 100 maple, locust, and river birch trees into the ground on Nov. 6.

To fans of all ages, she is, simply, "Mindy," according to Jane Pepper, Becher's longtime predecessor at PHS.

In an e-mail from Heathrow Airport in London, Pepper writes: "Quite often I come across people wearing Tree Tenders T-shirts, some dating back 10 or 15 years. I ask them how they became involved in a tree-planting project. Invariably, they answer with one word - Mindy!"

Maslin grew up in Lafayette Hill, in Philadelphia, the daughter of an insurance broker and a ballet teacher. She was shy and uncoordinated - no ballet career in her future, for sure.

But even as a youngster, Maslin had what she describes as "an environmental ethic" that has defined her life ever since. One early example: When she was 7, a summer-camp counselor took her aside to ask if she was too poor to afford a new paper bag every day for her lunch.

"I didn't have the verbal skills to explain to an adult why it was wrong to throw things away after only one use," recalls Maslin, who buys secondhand clothes and household goods to fulfill her commitment to recycling.

One other piece of the worldview: Maslin became a vegetarian at age 12, in consultation with Pal, her pet collie. Today, son Samuel, 8, is of like mind; husband Sid Ozer is "vegetarian-sympathetic."

With time, Maslin's self-confidence and leadership skills grew.

She joined a Jewish youth group; became a VISTA community organizer in Iowa; lived on a desert kibbutz in Israel for a year; canvassed for political candidates and environmental causes around the country; and earned a degree in social work from Temple University while working full-time at Big Brothers Big Sisters.

From those experiences came maturity and some insights: that she was organized and energetic; that she worked well with others, including kids with tough stories; and that she could be persuasive.

"I could knock on a door and get invited to dinner," she jokes.

Looking back, you might conclude that when she finally got the PHS job in 1990 as "youth tree educator," it made perfect philosophical sense.

To get the kids pumped about trees, Maslin created a classroom game called "Environmental Jeopardy," like the TV show, and recruited a local rap singer named "Monte G." She can still do the rap:

"Hey, everyone in the place to be

Listen up 'cause it's me . . . yeah, Monte G."

"The kids were paying attention!" Maslin says.

That doesn't surprise Julianne Schieffer, urban forester with the Penn State Cooperative Extension, who bonded with Maslin 20 years ago over trees and does Tree Tenders training with her.

"20,000 trees planted . . . that's a lot of good air. Mindy's literally given us a burst of fresh air," Schieffer says.

Though she knew little about trees when she started, Maslin was in the forefront of an urban tree movement that now flourishes around the country. "Tree Tenders is one of the oldest volunteer urban tree-care programs in the country," says Nina Bassuk, director of the Urban Horticulture Institute at Cornell University.

The impetus now, she says, is the result of heightened interest in sustainability, worries over climate change and loss of trees, and a realization that maintaining trees isn't enough.

"Trees have a life span. They die, and you have to keep planting for the future," Bassuk says.

That's the deal with Tree Tenders, which PHS's Barley Van Clief, who coordinates the suburban groups, describes as "a very big thing that is really cool.

"We have finally gotten to a point where there's critical mass," she says.

Speaking of critical, Maslin warns her Tree Tender volunteers at the outset: "You'll never again be able to walk down a street in peace."

That's because - of course - the trees need tending.

Read garden writer Virginia A. Smith's blog at www.philly.com/philly/blogs/gardeningEndText

Tree Tenders

Pennsylvania Horticultural Society's Tree Tenders program offers nine hours of hands-on tree-care training for residents of the five-county Philadelphia region. The training covers tree biology, identification, planting, and care.

The next classes will be held at PHS, 100 N. 20th St., fifth floor, on two Saturdays, Jan. 15 and 22, from 8:30 a.m. to 1:30 p.m.

Fee: $25. Preregistration is required. It can be done online at http://www.pennsylvaniahorticulturalsociety.org/

Courses in Philadelphia, Delaware, and Montgomery Counties will be held in spring. Evening dates to be announced. Fee: $25.

For more information, contact Mindy Maslin at 215-988-8844 (Philadelphia), or Barley Van Clief at 215-988-8793 (Bucks, Chester, Delaware, and Montgomery Counties).