Stephanie Cohen's moment arrived more than 30 years ago, during her homemaker period, when she left teaching to stay home with her three children. One day, her husband came home from work to find her sitting on the bedroom floor, arduously polishing the furniture hinges with Brasso using a toothbrush.

He said something like, "It might behoove you to go back to school."

Cohen, now 70, doesn't remember much more, except that eventually she ended up at Temple Ambler taking a class or two about plants. "I loved it right away," she says.

With family obligations, it took Cohen five years to add a two-year horticulture degree to a resume that already included a B.A. from Temple University and five years teaching junior high school English and geography in Camden. She would soon earn a master's degree in environmental studies from Beaver College.

Now, Cohen is a nationally known author, speaker and horticulturist with special expertise in perennial plants.

Until she retired from the classroom in 2001, she had a long association (21 years) with Temple Ambler, teaching advanced perennial design, ecology and, occasionally, entomology and soils. She also was instrumental in establishing the school's Landscape Arboretum in 2000, serving as its unpaid director for the first five years.

"In many respects, Stephanie has been the face of the arboretum," says Phil Albright, cochair of the arboretum advisory committee and another key player in its development.

But it's perennials that have stoked Cohen's career. "When I hit herbaceous perennials in class, it was a meeting of the minds," she says.

Obtuse-sounding though their name may be, herbaceous perennials are simply plants that are all green and soft, unlike trees and shrubs, which have wood. Coneflowers, asters and black-eyed Susans are some common ones, much loved because they die down to the ground in winter and sprout again in spring.

Reliable and easy, herbaceous perennials are the mainstays of many gardens.

Cohen is so enamored of these plants, she's known as the "Perennial Diva" or "the Dr. Root of Perennials," a nod to Dr. Ruth Westheimer and their similarly short statures.

At 4 feet 7 inches, Dr. Ruth is a veritable sprout compared to Cohen, who's 4 feet 11 inches. So there. Still, the height thing seems to have lent a discomfiting definition to Cohen's identity in gardening circles.

"After all these years, I still get short jokes," she says with a sigh.

So she beats the jokers to the punch. She calls herself "The Dwarf Tornado." She champions "vertically challenged gardening," and the sign beside her driveway in Collegeville reads "Shortwood Gardens."

"Because Longwood Gardens is taken" is her stock one-liner. It never fails to draw a laugh.

Cohen lectures around the country and is a contributing editor for Fine Gardening magazine. She's written two books, the first of which - 2005's The Perennial Gardener's Design Primer (Storey Publishing), with Nancy J. Ondra and photographer Rob Cardillo - has sold 60,000 copies.

Not bad for a gal who, times being what they were, once faced three realistic career choices - secretary, nurse or teacher - to complement her "M.R.S." degree.

"I thought, 'I can't type, and I can't stand the sight of blood. I guess I'll be a teacher,' " Cohen recalls.

Perhaps inspired by her uncle the lawyer, or maybe too much Perry Mason, she initially thought she would make a decent lawyer. But a male pre-law instructor discouraged her.

"Which is why I told my own kids to be whatever they want to be," says Cohen, who is married to Dick Cohen, a dentist. They have three children - two daughters and one son, ranging in age from 36 to 43 - and granddaughters 2 and 5.

Till she was 5, Stephanie Sherman lived in New York City with her parents, who moved the family to Camden to work at RCA. Being native New Yorkers, Cohen says, they weren't too "green," but they did reflect the trends of the times: They grew vegetables in a victory garden and marigolds and zinnias from seed, and African violets filled the windowsills inside.

Next door was an open field, where Stephanie roamed to a degree unheard of now, especially in a city. Early on, she also loved reading the classics and writing. "I was a weird kid," she says.

Not so much weird as smart. And, as an adult, more serious than some might think. "Everyone knows my silly side. They know I can be pretty irreverent," Cohen says, "but I actually have a very serious side."

Nancy Beaubaire, a horticulturist and communications director at Bowman's Hill Wildflower Preserve in New Hope, has seen more sides of Cohen in their 30-year friendship than almost anyone else. She was Cohen's editor years ago at two gardening magazines. She took Cohen's perennials class at Temple. And, in 1998, she met her husband, Steve, through the Cohens. (He's Dick's brother.)

"Stephanie uses humor to draw people in. That, plus her experience, makes her one of the top horticultural speakers in the country," Beaubaire says, citing her sister-in-law's gigs at garden clubs, trade and flower shows, professional organizations, and schools.

And Cohen easily speaks her mind in the horticultural world, which is just as full of hot air, vested interests and commercial hype as any other. When a professional plant-grower asks her to "trial" or test a new plant, she says, "they get the good, the bad and the ugly."

Cohen called a new daylily bred by a well-known hybridizer "a real bowwow," and has no problem advising gardeners to take a pass.

"If it's crap, I'll say it's crap," she says.

John W. Story, general manager of Meadowbrook Farm in Abington, which grows indoor, garden and exotic plants, says Cohen is "highly regarded for her teaching and knowledge. Everybody knows Stephanie. She lays it on heavy."

She's a pistol, all right, and a favorite with former students, of which the Philadelphia region has many.

Shelley Dillard, Morris Arboretum's plant propagator, studied with Cohen in the 1990s and delights in knowing that "now we're colleagues."

"Stephanie's turned a lot of people on to perennials," Dillard says.

And not just in the classroom. Last year, Storey published Cohen's second book - Fallscaping, again with Ondra and Cardillo. She's working on a third, for Timber Press, about mixed borders, and will likely do many more before she hangs up her trowel.

"Gardening is not rocket science," Cohen likes to say. "It's a skill."

One, it seems, even a perennial diva had to learn.

Virginia A. Smith writes about gardening at http:// go.philly.com/kisstheearth