PHILADELPHIA -- Everywhere you look these days, bamboo stuff is for sale -- cutting boards, pizza paddles, paneling. And bamboo flooring is all the rage.

But bamboo in the back yard? Whoa! Where'd everybody go?

A lot of gardeners run for cover when the word is mentioned. But Phil Schumacher, a true "bambusero," just grins.

"They're kind of mystical plants," he said.

Mystical and lithe and lush in a way that other plants just aren't. Their canes sway in the slightest breeze, creating dancing shadows and a whooshing sound that hints at paradise and serenity. And blooms are mysteriously rare.

But bamboo also has a deservedly menacing reputation. More accurately, the bamboos that spread aggressively, simply doing what comes naturally. It's their keepers who fail to control the rhizomes, or underground stems, which can shoot out as many feet as the plant is tall in just a month or two.

"You just need to understand the plant," said Schumacher, a retired engineer who has about a dozen bamboos -- aggressive and not -- in his half-acre garden in Wallingford, Pa., outside Philadelphia.

That's the key to understanding bamboo, which is classified as a grass: the difference between aggressive and not.

Running bamboo, which includes many in the Phyllostachys genus, is the aggressive kind. You don't want to plant it close to anything else.

Schumacher has one by his garage, called Sasa veitchii, that's pushy -- and pretty. It's three feet high, shrublike, with large broad leaves that turn creamy around the edges in winter.

For a dozen years, he also grew a striking Phyllostachys nigra, or black bamboo, that was 18 feet high and 6 feet in diameter, with jet-black canes. Like many runners, it was evergreen and, Schumacher said, "breathtakingly beautiful throughout the year, particularly in winter."

The sight of snow against the black canes and green leaves is "almost a transcendent experience, so lovely," he said, "especially when the sun hits it right."

(After 20 years, Schumacher has given away his black bamboo and many others. They'd become a lot of work, and he's moving slowly toward another horticultural fixation: camellias.)

Clumping bamboo, which includes many Fargesias, isn't invasive or necessarily evergreen, and its canes are often shorter and smaller. It typically expands outward four to six inches a year, like an ornamental grass, with new canes pushing up close to the clump.

All bamboos produce canes or shoots, called culms, in spring. They get their legendary strength from silica, which is produced by decaying bamboo leaves and stems on the ground.

Harder than oak, bamboo has been known to pop chains off a chain saw and dull the sharpest blade. It has withstood hurricanes, and groves of it survived, with scarring, the 1945 atomic blast in Hiroshima.

Still, bamboo's beauty is what hooks most gardeners.

Fifteen years ago, Jim Shannon planted two small clumps of Phyllostachys vivax, a runner, on his 1 1/3 acres in Perkiomenville, Pa. He'd found them in a field across the street.

Today, those modest clumps are a 35-foot-tall grove held in check by a hard-plastic rhizome barrier that goes down about three feet. Shannon has hacked a path through it all, and even on a recent rainy day it was magical.

No rain penetrated the fluffy canopy, but wind tripped lightly through the canes. Leaves fluttered in the muted rush. Lots more had fallen, making a mat so thick my feet wobbled as we walked along, as if on a big soft bed.

Shannon, whose company, Bamboo Habitat, sells bamboo products, chatted on about the nutty taste and celery-like consistency of fresh white bamboo shoots, which he cuts just beneath the soil, like asparagus, peels back and eats right there in the yard.

"I like bamboo a lot," he said, grinning the same way Schumacher does when he talks about this stuff. (In fact, I'm thinking, like so many things in the seemingly placid world of gardening, bamboo is sounding more and more like a cult.)

Shannon sells bamboo poles, wall coverings, fencing, thatching and plants. He emphasizes that the live plants, also available at some garden centers and big-box stores, remain "a little niche market. Bamboo's not for everybody."

But more and more folks are wanting it. They often call Shannon after they've seen running bamboo somewhere and are knocked out by its dramatic look and size. It grows so fast, and so tall, they're thinking that in about three years it'll be a perfect privacy screen.

JoAnne Wyman, president of the American Bamboo Society, said that's "the most popular thing in bamboo right now -- the screening for privacy. People are really out for something that will block their view of a neighbor, especially in suburban developments."

Trouble is, without a high-density polyethylene plastic, concrete or water barrier, running bamboo will soon leap out of control, overpowering your daylilies and causing war with the neighbors. No joke: You'll need a backhoe to rip it out of the ground.

"If you put it in without a barrier, you're asking for problems," Shannon said.

Clumping bamboos are an alternative screening, although their slower growth and generally shorter stature may not satisfy some, said Michael Bartholomew, a founding member of the bamboo society's Northeast chapter, which includes Pennsylvania and New Jersey.

"If somebody's looking for that bamboo look, they're not going to get it as well from a clumping bamboo," he said. "You really only get that from a running bamboo."

Bartholomew, a consumer horticulturist with the Cornell University Cooperative Extension in New York, grows 20 bamboos on his 13 acres in Albany. Nothing mystical about it, he insists in a telephone interview.

"They do give you a kind of, almost like a feeling," he said slowly, "from the sound and the look, a very nice feeling."

Sounds like a grin to me.