Beware garden thugs – invasive plants

"Baby's breath." The very name hints at gentleness, a perfect label for a plant best known for airy sprays of tiny flowers that act as a bouquet backup to more spectacular blooms.

So you're likely to do a double take at Camp Ripley (the National Guard training facility near Little Falls, Minn.) and around Park Rapids and Brainerd, where robust stands of baby's breath have popped up in the landscape. With a taproot and a tendency to break off and bounce across the ground like a tumbleweed, spreading seed as it goes, baby's breath has become enough of a thug at Camp Ripley that alarmed officials are spraying fields with herbicide.

Is baby's breath on its way to joining other once-valued garden plants that are now on the state's blacklist of invasives that threaten Minnesota's environmental or economic health? Possibly.

"I'm an avid gardener," said Monika Chandler, invasive plant expert with the Minnesota Department of Agriculture (MDA). "When we learn that a plant is invasive, it's a serious bummer for us, too. These have been really popular plants."

Over the past 200 years, several thousand foreign plant species have naturalized in the U.S., and about one in seven have become invasive, according to Cornell University. Many of those plants were imported for their value as landscape and garden plants.

Thirty years ago, pink-flowered crown vetch was widely planted to stabilize slopes along Minnesota highways and roads. Purple Japanese barberry, with its thorns and fascinating shiny oval fruit, was a fixture in foundation plantings around homes. Buckthorn hedges were common in older neighborhoods. And I bought supposedly sterile hybrid lythrum from one of the nation's best-known perennial merchants, planted it in my garden and loved the plant for its beautiful flowers and statuesque presence in the perennial border.

Today, crown vetch and buckthorn are on the MDA's restricted noxious weed list and cannot be sold or intentionally planted in the state. Lythrum, better known by its common name purple loosestrife, is on the MDA control list to prevent its spread. (My plants produced seedlings within a couple of years, of and I removed them.) And next year, Japanese barberry will join crown vetch on the noxious weed list. Birds eat and spread barberry seeds, producing brawny green barberries that naturalize in the woods.

While lots of plants romp through the landscape, for the MDA it's a matter of degree, she said. Siberian squill, the tiny spring-blooming bulb with nodding blue flowers that naturalizes in lawns, is considered an invasive by many but it isn't going to do much economic harm or hurt livestock, Chandler said.

Contrast that to the knotweeds, a plant that she's working to assess now.

Japanese knotweed (polygonum cuspidatum) is sometimes called hardy bamboo in Minnesota. The towering plants were a favorite landscape feature in 19th-century gardens. The problem, Chandler said, is that polygonums have no natural enemies. They are early plant colonizers after volcanoes erupt, can pierce hardened lava and, in more civilized landscapes, can break up asphalt, concrete and even house foundations.

The plant is considered a serious threat in England; removing it from the London site for the 2012 Olympics cost the equivalent of $120 million, Chandler said. Chemical treatment to kill the plants takes three to five years.

The MDA is investigating a mystery stand of knotweeds near Duluth, Chandler said. She thinks the plants are a hybrid of some kind, though it isn't clear where they came from or how they got there. The state collected flower and leaf samples last summer, and is conducting a genetic study to identify the plant and testing to see if viable seed is being produced.

"You can't figure out how to manage it if you don't know what you're dealing with," Chandler said. "After that, outreach and education is critical, and working with management plans."

So what role do gardeners play in controlling invasives? Chandler says they can build healthy landscapes by using information available at websites like the University of Minnesota's sustainable urban landscape information at extension.umn.edu/garden/landscaping/, and by paying attention to bulletins about plants like oriental bittersweet and buckthorn, which many people have removed from their yards.

Gardeners aren't alone in their efforts. Chandler said plant breeders are working on seedless varieties of plants like Japanese barberry, which were valued by landscapers and homeowners for their purple, maroon and red coloration and attractive form.

"Nobody wants to lose these as garden plants," Chandler said. "We would much rather see these stay on the market, but be safe."

As for baby's breath, the jury is still out. Chandler said it isn't clear if plants have spread from dried bouquets that had viable seed in them or from plants that are self-seeding. Baby's breath is already listed as a noxious weed in Alberta.

For more information on the state's efforts to fight invasives, check out the MDA website at mda.state.mn.us/plants/pestmanagement/weedcontrol.aspx.