The old Iris Brown was, like many of her neighbors, scared and alienated and living from moment to moment in the late '80s, in a North Philadelphia neighborhood no one ever imagined would be so hopeless. Then the horticultural society, the same people who put on the Philadelphia Flower Show, came around to the place where she lived.

The neighborhood had plummeted into a stunning cycle of failure, a cycle twirled by violent crack pushers and brazen whores, intermittent gunfights and wholesale urban flight. If the horticultural society people who came to the neighborhood were scared, they didn't show it. They were the opposite of hopeless.

Tentatively, then firmly, Brown was caught up in their ideas. She could learn to plant and tend trees. She could help make gardens bloom from trash piles. And: She could organize. She could be a leader. The new Iris Brown eventually exploded from out of the old one.

She tells me this after I've walked in on a session she's having with one of the people who has worked for a decade with the residents, Eileen Gallagher, a staff member for the Pennsylvania Horticultural Society's Philadelphia Green program. When I ask what the two of them are doing, Gallagher says without missing a beat, "Oh, we're planning the future," and she and Iris Brown burst into laughter. I do too - it's funny to hear someone say a sweeping thing so seriously. Even if it's probably true.

The future that the Pennsylvania Horticultural Society has been working toward, for decades, is here, now. PHS - that's what everyone calls the society - marked its 175th anniversary in 2005. It is the nation's longest-running group of big-deal horticulturists and backyard green-thumbers, plus tree huggers, flower lovers, ground kissers, and just plain hangers-on who like to be among its 12,000 or so members, and who get automatic tickets to the flower show.

For the last 40 years, the society has been on a trajectory that has taken it far from the traditional gardening advocate and directly into the daily life of the region - and particularly the city of Philadelphia. The horticultural society is no longer just about flowers and trees. It's about the way the city looks. It's also about the people who live here and what the city means to the quality of their lives.

The society does things for Philadelphia that other cities pay people to do or wish they could pay people to do. That's why Baltimore, Milwaukee, Atlanta, Cleveland, and Portland, Ore., have put their magnifiers over the society to try to figure out how its projects work. That's why Spring Garden Street's wide and once barren medians exude warm-weather green. It's why that long stretch along JFK Boulevard to 30th Street Station - a few years back, a solid monument to the way urban trash takes over - has a lush and vibrant look. It's why 40 city parks, large and tiny, are not former city parks.

The society makes some of this happen by teaming with corporations and foundations that can help pay for landscaping and maintenance. Pew Charitable Trusts, for instance, recently pledged $900,000 to the society for its strategy for making the city green, and keeping it that way. The society accomplishes the rest of its work in the city by getting residents organized, trained and working for their neighborhoods.

This community-building has changed the look of many low- and middle-income places, and not just that. It has imposed a new order on some neighborhoods, where the former plant society has taken off into many other improvement efforts. The society is the legacy of the activism, even the radicalism, of the '60s.

To its staff, reclaiming the broken parts of Philadelphia is not a mission but a passion. These are people who, in the turbulence of the '60s, could easily have plugged flowers into the muzzles of rifles. Now, they are plugging them into foundation grants and legislative proposals. And along the way, they reach people like Iris Brown, whose former urban hell is a lot more, now, like Eden.

If you need proof, drive down a narrow residential street like Palethorp, around the intersection of Dauphin Street, in North Philadelphia. Even now, when nothing blossoms in the winter freeze, you can see the sites of garden after garden on lots both vacant and owned. The people made the gardens. The society gave the people the courage to go clear them and the tools - and most of all, the organization and know-how to do it.

"The horticultural society is about people and plants," says J. Blaine Bonham Jr., the executive vice president who oversees the society's vast community projects, which generally operate under the name Philadelphia Green. People and plants, he says, and in that order.

The ideas that Bonham and his colleagues employ come directly from old-school community builders: Organize people. Give them gardening and tree-tending skills. Turn them into a network. Help them make "greening" part of a larger plan for the neighborhood. Be certain they have the resources and know-how to keep the gardens growing. Stake their relationship with the society by giving them more workshops, more hands-on training about community-building, not just planting.

Simple? Yes, at least on paper. In practice, it's a heady mixture of energy, commitment and people skills - and plans as intricately conceived as the veins of a leaf.

It doesn't always work, not right away. Marcy Hetelson, 34, a ward committee person and graduate student at the University of Pennsylvania, has been involved with the society for a year now, because she wanted to do something about the vacant lots in her neighborhood, around 25th and Christian Streets, south of Center City.

First, she joined Philadelphia Green's program called Tree Tenders, which has trained more than a thousand people, who then train others, to plant and maintain trees. Then she turned her attention to Garden Tenders, which has the same general idea:

"We train you to do it, you do it, and we keep the network going," says society education director Eva Ray. So far, Hetelson has managed to get eight tree-tending neighbors. This spring, they'll get three blocks' worth of street trees, and the society has trained them to cut the tree space in the sidewalks, dig the pits, plant the trees, and maintain them.

The trees and other planting materials are coming from both Fairmount Park and the society, which have built a remarkable relationship. That arrangement, from the society's point of view, is simple: We have an urban mission, skills and a track record, you have skills and needs. If the two of us blend our skills, we can help fill your needs.

As for gardens, Hetelson has so far struck out. Among the many skills the society must teach are bureaucratic ones - for instance, finding out who owns vacant land and getting permission to make it bloom. Hetelson has been stymied, because the owners of many lots will not let other people claim the land for gardening, even temporarily.

"It's tough, but we'll get there," she says, without an air of resignation. "I learned from PHS how to get the community together to do these things - what to do, how to do it, and what the benefits would be. They've motivated me. We've formed three different organizations just because they got us off the ground - a Tree Tenders, Garden Tenders, and a Town Watch. We're so excited about the neighborhood again. We've got a vibe going that hasn't been there before."

That vibe, powered by people but carefully set in place by the society, hums in many ways, some of which are classic horticulture endeavors and some of which might be called lessons in advanced flower power. You find it in a room at society headquarters, at 20th and Arch Streets, where about 75 people gather for a four-session course on the Latin names for plants. Or in the suburbs, where people may be learning to make and keep a trough garden, or may be hiking to learn the different trees. Or in its endeavors as a heavyweight in the world of horticulture, such as the Gold Medal award to recognize often underused plants of merit, and its Web site service that fields questions from gardeners.

You find it at the Friends Meeting House at Fourth and Arch Streets, where the society may be running a workshop on how communities can fend for themselves in a bear market when foundation and city budgets are pinched. That particular program is based on finding the talents and simple resources that people in a neighborhood already have, rather than "seeing your community as something always needing - needing, needing, needing," says Mindy Maslin, the society's chief of all Tree Tenders.

You can sense the vibe, of course, at the flower show, or at the more down-home harvest show in Fairmount Park each fall, or at the contests for the most beautiful gardens across the city. You sense it when the society takes on yet another project, as it did a few weeks ago; Fairmount Park announced that society-trained tree tenders would roam the city taking an inventory of many of its 250,000 street trees, whose individual characteristics must be put into a database so the park can begin an ambitious pruning program.

You sense it when you see the azalea garden behind the Art Museum, which the society maintains for the city, or the lush plantings along 26th Street approaching the airport, which the society installed in partnership with Sunoco. Or when you see society-trained volunteers, pruning shears in hand, on the Art Museum's grounds.

These alliances and projects raise important questions: Has the horticultural society become an unelected arm of city government? Shouldn't the city be taking on many of the projects the society is running? The questions become more relevant as the society becomes more relevant in the everyday life of Philadelphia - and begins to take a major role in the city's new war on blight. The recent $900,000 Pew grant to the society is partly for policy-making. With it, the society - not the park commission, not the planning commission, not the managing director's office - will lay out a long-term strategy for Center City's public landscapes.

Bonham says foundations often ask, before approving grants, whether the society is going to be doing work the city government should do. His answer: "If the city is in the kind of financial state it's in and this is an effort that demonstrates our potential, then it's worth doing. If it tries to completely replace a function the city needs to come to grips with, it's not a good way to go."

That seems a fine line, easily crossed.

"You can make the legitimate argument that things shouldn't have to be this way," says Ted Hershberg, the professor of public policy at the University of Pennsylvania who heads the issues-oriented Center for Greater Philadelphia. "The reality is, they're doing stuff we all benefit from, so given a choice of stepping back and having the city do whatever it can - I don't think we would want that."

Hershberg says the society is in the same league as the Center City District, which cleans streets and has taken on the marketing of downtown Philadelphia. Neither is part of government, officially. But they perform some of government's traditional roles.

"The cost of providing these things exceeds the revenue from all sources," Hershberg says. "You thank God you have all these quasi-public and nonprofit organizations to pick up slack."

In the case of the horticultural society, not only do people thank the heavens, they do not bad-mouth the organization. Reclaiming the earth and turning the ugly into the beautiful are apparently enterprises that people like - regardless of organizational charts and separation of powers.

"We want to try and help them as much as we can," says Edward C. Coryell, executve secretary of the Carpenters Union, whose members work at the Convention Center, where tales of imbroglios growing from union work rules have been making news. Coryell has only praise for the flower show. Ed Lindemann, the society's flower show chief, "has been great. He's a gentleman. We try to help him in keeping the cost down. We do as much with him as we possibly can to help them keep the cost down. PHS works for a good cause."

"Horticulture is universal," says Ernesta Ballard, the celebrated activist who turned the low-key horticultural society into a civic force after she took over in the '60s. "The whole point for (the new) PHS was, we'll show you. We'll bring the topsoil and we have the truck. You have to spread it. You have to plant it. And you have to maintain it."

Ballard groomed Jane G. Pepper, the current president (and a garden columnist for The Inquirer), who in the last 23 years has steered the society into the position of primary mover and shaker. Pepper has managed that with a growing staff, plus many trials and errors. ("We've developed and tested many models," Bonham says.) Pepper's style, and that of the society, is to consider an idea until the probable impact and the risks are understood as fully as possible. This takes time, and if you ask people at the society about the planning process, they are often given to chuckling because the process can be, well, exhausting. For Pepper's part, that is just fine.

"PHS is definitely a democracy and that's the way I like it," she says. "I don't have all the answers. Blaine doesn't have all the answers. I want to include people in all the decisions we make. And once we make them we move very fast. We are not a reckless organization. With Philadelphia Green, a lot of planning goes into what we do. There's no textbook."

This type of management - lots and lots of information-gathering, then an unwavering course of action - has given Pepper a reputation. "I believe Jane Pepper could manage a steel mill, I really do," says J. William Mills III, president of PNC Financial Services and a former flower show chairman, who has put her on his bank's board of directors.

Of the society's 103 staff members, 75 are women. Lots of people who work at nonprofit corporations are female, but the society's number seems high. When I asked employees how the culture of the place was affected by so many women, in every instance, the question was greeted with quiet bafflement. People had to think about it before responding.

"It's a question - I don't know, that's a hard question to answer," says Patricia Schrieber, who manages the society's outreach efforts into neighborhoods. "Maybe it's this: As conscientious as we are about getting bread and butter on the table and making a living, we have a strong sense of social responsibility." Says Eva Ray, the education director: "I don't think it does affect the culture. I see the men being inclusive as much as the women." Pepper says, "It's never really sunk in that way. Wouldn't you think that in a nonprofit, there'd be more women than men?" Ballard takes a no-nonsense approach. "It's nonprofits that have women leaders. I can't romanticize about it. They have the capabilities."

"It's not high on the list of things we recognize," says Michael W. Groman, the director of Philadelphia Green. That was generally the feeling - remarkable, in a sense, because the society may have achieved the sort of gender-blindness that activists also sought four decades back. It makes sense, really, at a place where people still live by a clear grassroots building concept. Literally. Figuratively, too.

I am with Iris Brown, upstairs in a meeting room at the Norris Square Neighborhood Project, to the far east of Temple University, tucked into the southern part of a swath of North Philadelphia called West Kensington. If I asked you to guess, realistically, how many vacant lots are in that single city neighborhood, where the residents are largely people who came here from Puerto Rico, you might say, oh, maybe 200 or 300. (And then think that you went too high.) Correct answer: 1,100. If I then asked how many of those lots the residents rescued after the horticultural society empowered them with solid gardening knowledge, plants, soil, tools and the skills to maintain their work, you might say, perhaps 100, maybe 200. (And then think that you went too high.) Correct answer: about 550.

The people of West Kensington have reclaimed nature in half their derelict spaces. They've also reclaimed their dignity, a connection with their neighborhood, and spaces bigger than vacant lots. Iris Brown is about to walk with me through Norris Square, near Second and Diamond. It's as big as Rittenhouse Square. Fifteen years ago, people called it Needle Park for obvious reasons and residents would not cross through, even to go to church on an early Sunday morning. Drug pushers and junkies owned the park, and a falling-down shack on its grounds was great for the sex trades. Trees were old and untended, and Brown remembers seeing large branches scattered after storms.

Brown helped the horticultural society round up enough volunteers to learn tree planting and maintenance - "the majority of people were afraid" to even consider the idea of wresting control over their large park and their treeless curbsides, she recalls. At one point, the city came in with its own plans for Norris Square. Officials told people they would be getting a fountain in the middle of the park. Iris Brown, whose native language is Spanish, was becoming more fluent in English, and she finally got mad, instead of her usual demeanor at meetings, which had been intimidated and silent.

"The city officials came to a meeting with their suits and all their drawings. I said, 'I hate to burst your bubble about these fountains, gentlemen. I am looking at these drawings for a fountain. Here is what I see. I see people taking showers. I see water, very dirty. I can see syringes in the water. I can smell the urine in the water. I don't see the wonderful fountain you have in those drawings.' With PHS, we knew we could sit down with the community and bargain. We already had respect for each other."

Brown and I bundle up in layers and walk the paths of Norris Square on a weekday morning that delivers the bitter sting of this Philadelphia winter. Almost no one is out. She points to the new trees, the tables for playing dominoes, the tile artwork at the entrances, the large playground that took the place of the proposed fountain, the art insets in the sidewalks, the pleasant landscape. The extreme chill becomes merely part of the invigorating context of the place.

Back inside the Norris Square Neighborhood Project offices, women of several generations are busy. The women are making the same costumes as those in a 10-day festival at Iris Brown's original home, the town of Loiza, Puerto Rico. Next week, for the eight days of the flower show, their work will adorn dancers at the central feature, executed this year by Robertson Florists of Chestnut Hill. The theme of the show is Festival de las Flores, or Festival of the Flowers.

If you have the reach of the horticultural society, so broad and diverse that it takes in the suburbs' most elite landscapers and the inner city's most struggling residents, you are going to have instant resources. So when Lindemann conjured the Latino theme for the 25th flower show he has designed and is directing, he needed only invite the society's friends, the women of Norris Square, to jump in. They were ecstatic. So was he.

A few weeks ago, society members and nonmembers from across the area signed up for an unusual behind-the-scenes flower show tour. First, they went to tony Chestnut Hill, where Bruce Robertson and his staff shared the secrets of the opulent main exhibit, whose flowers are being forced into springtime. Then, the group headed to North Philadelphia, to neat, reclaimed Norris Square, for "the culture that inspired the horticulture," as the society's events listing declared. Iris Brown and the women served a Puerto Rican lunch, then showed the fruits of the dressmakers' labors.

What began in 1827 as a bunch of local guys promoting gardening - with some big ideas, given the state's name in the title - first morphed into a group that served loosely aligned garden clubs across Philadelphia and do-gooders who ventured into "those" Philly neighborhoods to give the people some beauty.

It was "too much like Lady Bountiful," Ballard says. "I thought we needed young people in blue jeans, not the gardening-club ladies." She got them, and was able to keep the gardening-club ladies, too. She hired Pepper and Bonham, and the small staff helped with a window-box program, then expanded to vegetable gardens, and, by the late '60s, something called the Garden Mobile began roaming the city.

"Three-quarters of the people on a block would have to put up $5 to make a garden," Ballard says, "and we would come out and show them how. The Philadelphia Foundation gave us $7,000 to run the program." All along, the staff was putting more effort into making the flower show more visible and more important, at one point getting architect Vincent Kling to help design it. It began to make money, and with that money, the society was able to enlarge its idea of getting people to appropriate their neighborhoods.

Today, the society considers all of Philadelphia its domain for making nice things come from the earth, and even now that would not be the case without the flower show. It's true that money does not grow on trees, but the flower show is a proven exception. It has a budget of about $6 million, enjoys international recognition, generates about $25 million in peripheral revenues for the city, and nets about a million bucks for the society each year.

The $1 million profit is the seed money, so to speak, for the entire organization. It, along with membership fees, helps pays the rent on the headquarters, and pays for some of the handsome and significant horticultural library and the society staff. Most important, it provides the basic funding stream for Philadelphia Green. Philadelphia Green has had such an impact that nursery owners feel good paying a lot of money for the exhibits they create at the flower show, where they also get exposure in front of 275,000 passersby.

"Philadelphia Green is all of the community outreach programs PHS does, so by keeping the flower show viable, we're in turn doing our part to help that," says Michael Petrie, who designs the show's exhibits for J. Franklin Styer Nurseries in Concordville, the longest-running exhibitor; this will be Styer's 103d show. Four thousand people - count 'em - will come from all over the region this week and next to volunteer at the show, doing everything from leading workshops to helping people off the buses at the Convention Center door, a group people refer to lovingly as the Grumpy Old Men.

"The hottest ticket in town is to be able to volunteer at the flower show," says Morris Cheston, a law partner at Ballard Spahr who has been a society board chair. "Can you imagine that, 20 or 30 men volunteering to stand out in the cold on the sidewalk, getting gassed by exhaust from the buses, to help people off? You're not going to get that at Eagles games."

Foundations and corporations also want to be part of the society, and want to be visible at the flower show, because the show's proceeds make Philadelphia Green happen. This accounts for the society's $28 million in net assets - all its investments, all money coming in, and all promised grants.

The society is operating, this year, on a budget of $15 million, which includes the flower show, the citywide projects, everything. By contrast, Fairmount Park must manage its 8,900 acres and oversee all the city's street trees with a budget of about $14 million, which has been virtually flat and frozen for about two decades. No wonder the park and the society have grafted; at root, it's a combination of missions and resources.

In fact, the society has become so deeply ingrained in the city's fabric that people attribute to it all sorts of things. Need a tree planted at curbside? Folks think they can call the society and, magically, a tree grows in Philly. (It doesn't happen that way.) Want to visit Horticulture Center in Fairmount Park or hold a celebration there? (Sorry, call the owners, Fairmount Park. Not the society.) Won't the society come and clear this trashy lot? (No, but it will show you how - but first, please round up some friends to help you out.)

Given its reach already, now comes the hard part for the society. In a sense, the organization has realized many of its dreams and is involved in keeping them alive. And pumping them up. During the last mayoral race, the society was presenting papers that took in the scope of urban blight and addressed some solutions. The city has asked the organization to become a major player in its blight program, called the Neighborhood Transition Initiative, and the society is eager. Mayor Street calls the society a "vital partner" in the program and is quick to cite its "extraordinary contributions to Philadelphia." He and his staff have been meeting with the society to pinpoint the ways that it can manage more of the city's vacant land.

In the talks, the society is zooming in on at least six areas of the city it believes would benefit from intense projects. The even-closer partnership with government may force the society to write a new chapter in its textbook for making cities green, because these may be the group's biggest challenges yet. Certainly, the effort will mean that the society must expand, with more money, probably from government.

"We've spent 30 years getting here," says Bonham, the society's vice president. "We think we have a formula for the city that seems to work. Does it cost money? You bet. It's not like building a whole new housing project for $50 million - although it probably could cost that much in initial investment and maintenance. We'd certainly have to increase our capacity and we need the resources to do it.

"And we're the ones to do it. We've got the systems. We've got the knowledge base. We've got the capabilities." That may sound like braggadocio, but when you have an indisputable track record, you're also likely to take a can-do approach. Besides, when you're the Pennsylvania Horticultural Society, there's always new ground to cover.