For gardeners, who often joke that their hobby is an addiction, this time of year can be cold and cruel, indeed.

But horticultural obsessives can still indulge in that second-favorite pastime: planning far-away garden tours in the new year.

Like time-pressed birders and bicyclists, oenophiles and hikers who gravitate to vacation spots and organized experiences that enrich their passions, gardeners constitute their own niche travel market.

No one tracks the numbers, but everyone agrees this market is small, intense - and loyal.

Joan and Jack Harvey of Haverford have been on five garden tours with the Pennsylvania Horticultural Society: two to England, two to France, and one to Australia and New Zealand.

They've marveled at a sheep farmer's lowland plantings on New Zealand's South Island. They've reveled in the romantic green of Normandy. And they've felt like royalty among the border beds of Farleigh House near Bath, England, the home - "quite large," Joan Harvey says - of the Earl of Portsmouth and his oh-so-down-to-earth countess.

"So many memories and adventures," Joan says.

Though botanical tours don't involve trekking in the Andes or hiking in the nude, those who have taken, booked and guided gardeners on these leafy outings insist they're adventures of a different sort.

Vicky Mary, spokeswoman for the American Society of Travel Agents and owner of Victoria Travel in Cincinnati, explains how:

A normal tourist sees a plant and may remark, "Oh, gosh, that's a pretty flower," and continue on. A gardener comes upon the scene, stops dead, and exclaims, "Isn't that an amazing rhodo! Wow! Look at the shape of the flute, the size of the leaf. Feel the velvet! Look at the base. How much lime do you need in soil?"

And on and on.

Mary, a rhododendron freak, rhapsodizes about the first time she saw a 12-foot-tall rhodo, at Leonardslee Gardens south of London.

"Hel-lo!" she chirps. "And what do you get in Philadelphia, a blossom maybe three inches? This one was eight inches!

"This sounds corny," she says breathlessly, "but I started tearing up. In my life, I'd never seen such a beautiful plant. It was orange-ish, with a huge trumpet hanging down, and the smell was breathtaking."

Mary visited those gardens 15 years ago, during a layover between flights, but the memory is clear and thrilling still.

"It was an out-of-body experience," she says, "which a normal person wouldn't appreciate."

But Julia Fisher definitely would.

"You can't really compare walking through a garden on your own to walking through a garden with a gardener," says Fisher, who works at JPMorgan in Philadelphia and has done both.

For the last two years, she and her husband, Art, have taken garden trips to England, and they've already signed up for a third next year. All are run by the Pennsylvania Horticultural Society. PHS president Jane Pepper, Scotland native and tour guide, says the trips fill up as fast as they're offered.

"These people absolutely love gardens," Pepper says.

The society has groups going to Holland/Belgium and England next year. And more international trips are out there.

In 2008, Horticulture magazine will take groups to Southeast Asia, Portugal and Italy. The American Horticultural Society has planned jaunts to India, Costa Rica and England. Locally, Scott Arboretum's New Zealand trip in January is full, and Morris Arboretum, which offers a garden tour to Mexico in October, already has more requests than spots for its New Zealand trip in 2009.

A handful of private companies offer horticultural trips, too, including Expo Garden Tours in Connecticut, Copper Beach Garden Tours in California, and ICanGarden.com in Canada.

England is the most popular destination, because of the common language, shared gardening traditions, and proximity, the latter's importance looming larger due to rising fuel costs and the falling dollar.

But mostly, English gardens are the favorite simply because of their number, beauty and variety. It matters little whether they belong to Prince Charles or the postman 'round the corner.

"Gardening seems to be part of the English soul," says Ann Granbery, a landscape architect from New Vernon, N.J., who's been on a half-dozen PHS tours to the United Kingdom.

Granbery's group actually did visit a postman's garden in Boston, on England's east coast. The man himself greeted them in a blue, three-piece, pin-striped suit.

"I don't even think he was 5-foot-tall," Granbery recalls. "He had enormous shoulders, perfect for carrying a mailbag, and he was the kind of person you couldn't forget."

To say nothing of his garden. "It was so cleverly laid out, so dramatic," Granbery says.

Joe and Liz Flanagan, retirees from Whitemarsh, love to reminisce about their Morris Arboretum trip to China several years ago, especially the Humble Administrator's Garden in Suzhou, some ancient bonsais, and, along the legendary Silk Road, the marvelous Buddhist caves and tea plantations.

Mao Zedong's private garden was a delightful surprise. "We came to a small lake where the moon rose up," Joe Flanagan says, "and there was the most romantic setting I have ever seen in my life.

"Mao was definitely not romantic," he adds, "but this was exquisite."

Travelers have always sought out beautiful places, whether here or abroad, says Judy L. Randall, president of Randall Travel Marketing Inc. in North Carolina, who has studied travel trends for 20 years.

Now, what she calls "time poverty" - the crazy, overbooked existence most of us lead - helps drive the market. "The idea of going to a place that affords serenity and tranquillity sounds absolutely divine to a lot of people," Randall says.

And many Americans can no longer take the traditional two-week vacation or the time to plan their own adventures. Many garden tourists say that, despite the considerable expense, they like the idea of someone planning everything for them.

For all those folks, Randall says, "shorter, well-planned, cruise-ship-on-land kind of trips to a garden are a beautiful thing."

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