Disease-resistant St. Croix elm making its way to Twin Cities garden centers

American elms once were known for their glorious leafy canopies spreading over city streets. But after the arrival of Dutch elm disease, elms became associated with garish blaze-orange rings painted around their trunks and the buzz of chain saws. The once-beloved tree quickly fell out of favor.

Now a new disease-resistant, homegrown option — the St. Croix elm — will be available in some local garden centers this growing season, although demand is expected to outstrip supply.

"I wish we had more plants," said Debbie Lonnee, a horticulturist with Bailey Nurseries, the wholesale grower that introduced the tree under its First Editions plant series. "We'll have a larger quantity next year. We think it's a great tree — we're very excited about it."

After years of testing, the tree has proven itself a survivor of Dutch elm disease, the scourge that has wiped out thousands of boulevard and back-yard elms in the Twin Cities and elsewhere.

"It's not immune," said Lonnee of the St. Croix elm. "It gets affected, but it has excellent disease resistance. And it's rock-solid hardy here in Zone 4."

The new tree has more than local roots. It also has an intriguing back story that attracted attention even before it hit the market, during the years it was being tested by University of Minnesota researchers.

The parent tree, a gigantic century-old elm, was discovered on a hobby farm in Afton.

Owner Chris Bliska had bought the property intending to start an organic orchard. The site was filled with elm trees, many infected with Dutch elm disease. But there was also one huge healthy elm, with a massive trunk about 75 inches in diameter. Bliska wanted to protect the tree, so he hired arborist and plant pathologist Mark Stennes to do preventive treatment. Stennes became convinced that Bliska's tree was something special and brought it to the attention of U researchers who were working on disease-resistant elms.

Over the next few years, U researchers tested the St. Croix's resistance to the max. They cloned seedlings of the tree, drilled holes in the bark at the base of the seedlings and filled the holes with a lab-concocted culture of Dutch elm fungus. Some of the young trees died quickly. But while others wilted and dropped leaves, they recovered.

"It's performed pretty well, comparable to the Princeton elm," said U plant pathologist Ben Held, citing another American elm species that has demonstrated disease resistance.

And unlike the Princeton elm, which hails from New Jersey, the St. Croix elm is ideally suited to Minnesota's growing conditions.

Disease-resistant elms are a hot topic among plant researchers and developers.

"Demand for shade trees is always increasing, and the American elm is an iconic tree, a very romantic tree," said Chad Giblin, research fellow in the U's department of forestry. U researchers are testing other promising elm varieties, including two American elms discovered on municipal land in Eden Prairie and the smaller native elm species Red elm and Rock elm.

Elms remain a nostalgic favorite of those old enough to remember the landscape before Dutch elm disease. "My generation, who grew up in the city with boulevard elms forming a shady tunnel, we remember that era," Lonnee said.

Dave Schulte, owner of Schulte's Greenhouse and Nursery in St. Michael, quickly ordered 10 St. Croix elms when he spotted them in Bailey's catalog last summer. He plans to grow the bare-root trees until they're a little bigger, around 6 feet, then sell them in August for $79.99. So far, his customers haven't been clamoring for the tree. "They don't know about it yet," he said, but a few of his peers have expressed interest. "Some other nurseries have called me, asking, 'How'd you get those? I didn't get any,' " Schulte said.

Gertens also expects to have some St. Croix elms later this growing season. They'll be potted, at 8 to 10 feet tall, and offered for sale at $99.99 in August, said Robin Dennison, tree specialist and nursery manager.

Don't bother looking for the tree at big-box retailers, at least not for a few years. "You're not going to see it in Home Depot or Lowe's right out of the gate," Lonnee said. "It will be in independent garden centers."

The St. Croix elm will have more regional than national appeal, Lonnee said. "This will sell for us best in the Upper Midwest. It was found in our back yard, and that will help this plant take off. Princeton elm is really well known and has a lot of legs on it. But it doesn't have the local back story."

The St. Croix elm's merits, in addition to disease resistance, are its abundant shade, vase-like shape and rapid growth habit, Lonnee said. "It's very fast-growing. It's a beautiful stately shade tree." And it's relatively low-maintenance. "It will need some pruning in the early years, then it's easy-peasy," she said. "It's not a messy plant," she added, noting that it produces small seeds, as opposed to the larger "helicopters" shed by maples.

Lonnee recommends planting St. Croix elms on a boulevard or in a big back yard, if you have one. But don't plant a small forest of elms in hopes of re-creating the leafy landscapes of the past. Today's smart landscaping is all about diversity and avoiding monocultures. "That's when you get into trouble," Lonnee said, citing the emerald ash borer's recent assault on ash trees.

"Who knows what the next thing will be?" said Held, making the case for genetic diversity.

For Bliska, it's satisfying to see the tree finally coming to market. (Stennes, who discovered and championed the tree, died last year.) "It's been a long haul," Bliska said. "I have high hopes for it."

He doesn't expect the tree to make him rich. "I spent some money getting it patented, and I would like to recoup that. I'll be happy if [the tree] gets out there."

Even though the tree has attracted some pre-release attention, it's unlikely to be a huge seller on the scale of an Autumn Blaze maple, Lonnee said.

"Good designers and landscape architects and city foresters looking for diversity in species will pick up on the tree and utilize it," she said. But it won't be the sexiest tree at the garden center. "It's not the most compelling tree from a color standpoint," she said. "It's a green tree that turns yellow in fall. It doesn't lend itself to today's retail scene, where people want to see the color."

But for those who covet a big spreading shade tree, the St. Croix elm may help bring elms back.

Meanwhile, the original St. Croix elm is still thriving, Bliska said. "It's great. I'm looking at it right now. It's still fabulously healthy."

Kim Palmer • 612-673-4784