When it comes to filling the concrete urns on either side of his front door, Ralph Mariani is a man for all seasons. He plants roses in spring, mums in fall, and tiny conifers at Christmastime.

Right after Thanksgiving, he trekked to Waterloo Gardens in Devon to buy two potted dwarf Alberta spruce trees, which by now he has plunked in the urns and decorated with festive red lights.

"They're pretty," Mariani, a lawyer from King of Prussia, says of his miniature trees. "It's something we do every Christmas."

Whether others do, too, is hard to say precisely. While the industry tracks sales of cut and artificial Christmas trees, no one apparently knows with statistical certainty whether Mariani is part of a growing trend. But those who study tree-buying habits in academia and observe it firsthand in garden centers believe he is.

"These are the new mums," says Tim Mountz, nursery sales manager for Waterloo in Devon, pointing to a bunch of potted Christmas trees ranging from 18 to 54 inches tall and selling for $14.99 to $80.

Dwarf pines, cypresses and spruces grown in pots for the holiday are certainly smaller and lighter than live trees whose roots are balled and covered with burlap. A 6-foot "B&B" hemlock can cost $129 and weigh as much as 250 pounds.

That's the equivalent of a Donovan McNabb. Imagine hoisting him into the back of your SUV!

So you understand why Mountz declares, "People got sick of all that. 'Balled and burlapped' trees are just too heavy. Sales are dying off."

Container-grown Christmas trees, on the other hand, were huge with Waterloo Gardens' customers last year, he says, and promise to be just as big this year.

Looking at these potted midgets, you might wonder at an emerging niche market that takes a centuries-old symbol of a favorite holiday, shrinks it to a perfect triangle, maybe attaches lights to it so you don't have to, then sells it to stick on top of a table or outside in an urn.

Clearly, this is not about sentiment. It's about convenience.

"They're a lot smaller and easier to handle, you don't have to cut the base of the tree, and they do very well in a condo or townhouse or smaller setting," says Nicholas Polanin, agricultural agent with the Rutgers University Cooperative Extension in Somerset County.

Problem is, Polanin and others say, most consumers treat their potted Christmas trees like "expensive annuals." They're supposed to be planted outside after Christmas; that's why they have intact roots. And that's part of the appeal: After you enjoy your Christmas tree inside, you do a good deed for the environment.

But more often than not, come January, the container trees get tossed on the poinsettia pile.

Even if you plant them, their future is iffy.

People may not care for them properly, forgetting to water, or put them in the ground at the wrong time. And a lot of the potted Christmas trees sold in this country are grown in places like Denmark and the Netherlands, so they won't survive in our climate no matter what you do, according to Ricky M. Bates, associate professor of horticulture at Pennsylvania State University.

"Somebody in Pennsylvania planting one of those outside after Christmas, thinking it'll be a nice landscape plant in their yard, doesn't have a chance," says Bates, who has been studying potted Christmas trees for three years.

So consumers need to look on the tag to see where the tree was grown, or ask the seller. Though it doesn't need to have been grown locally, the tree does need to be hardy to Zone 6 or 7, meaning it can survive winters in this area. (The trees sold at Waterloo Gardens should handle this climate just fine.)

Winter hardiness isn't a problem for Mariani's dwarf Albertas, those perfectly shaped, upside-down ice-cream cones that grow at the glacial pace of about an inch a year, up to about 10 or 12 feet.

But spider mites could be.

These tiny critters tend to be worse in hot, dry conditions, so Bates recommends planting the ever-popular Alberta spruce (Picea glauca) in a semiprotected spot with full sun through midday and shade in afternoon.

"You want a spot that doesn't really fry in the afternoon sun," he says.

This is starting to sound tricky, especially for folks like Carol Manning of Berwyn, who last year went shopping for simplicity. She and her husband had always had a live Christmas tree, but as the years went by they found that harder and harder to manage.

So Manning broke down and bought a "permanent" tree, a clever euphemism (like "preowned" car) for artificial tree. It's prelit, doesn't need water, and looks nice.

It also has no fragrance, its arms weigh a ton, and the box is enormous - 6 feet long. "You're not going to just take this to the attic," Manning says. "Who has room?"

But it was a $400 euphemism, and after such an investment, Manning feels she should hang in there and get her money's worth.

So while she's thought of getting a container tree, she's going to wait.

"Maybe when I'm 80," she says.

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Contact gardening writer Virginia Smith at 215-854-5720 or vsmith@phillynews.com.