How to control overbearing plant species in your home garden

This horror story starts so innocently. You bring home from the nursery a pretty little flower or a pert green vine. You give this new plant a home in your garden. Water it, feed it and watch it grow.

And grow and grow. It's wondrous how it thrives.

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But then, this single plant overwhelms its neighbors, expanding like magic to wipe out the competition. It strangles bushes, topples fences and can invade the house as it grows out of control.

"The British have a term for them: garden thugs," said Don Shor of Redwood Barn Nursery in Davis, Calif. "That's exactly what they are."

Many ornamental plants fall into this category. The most notorious: bamboo and mint.

When they sprout into wilderness areas, they become truly invasive, a danger to native species and a public nuisance. According to PlantRight, a program to fight invasive species, protecting California from such species costs more than $80 million a year.

Shor has a lifetime of experience with these green thugs, especially bamboo. His father was president of the American Bamboo Society.

"That's the No. 1 question we get: How do you control bamboo?" Shor said. "The bad answer is, plant the right kind of bamboo to begin with."

Bamboo comes in running and clumping species. The first send out underground runners that sprout anywhere. The "clumpers" stay contained.

"Everybody's brother-in-law has a horror story about running bamboo," Shor added. "If you plant clumpers, you can get the look without the headaches."

Shor suggested Alfonse Karr clumping bamboo as an example of a well-behaved variety. "It gives you that look that people want, but stays in one place."

Ellen Zagory, horticulture director for the University of California, Davis, Arboretum, has neighbors with running bamboo, which means she has bamboo shoots constantly coming up in her own yard.

"It's really scary," she said. "I've seen concrete patios where every little crack and seam had bamboo coming up. When I see some come up, I dig a big, long trench down as far as I can go and get as much as I can."

Running bamboo may be contained by root barriers, solid sheets of fiberglass or other material buried 2 to 3 feet down.

"But you've got to monitor the barriers," Shor added. "The runners can go right over or under them."

As for mint, Shor planted one spearmint from a 3-inch pot. "It now covers an area 10 feet wide -- all from that one tiny plant."

"Mint is No. 1 (among problem plants)," said Joan Coulat of Capital Nursery, based in the Sacramento, Calif., area. "I had a dilly of a time with mint. I'm smarter now. People shouldn't put it in to begin with."

"Powis Castle artemisia (or wormwood) is another that really gets going with low water," Shor said. "It's a cute little plant in the herb garden, but it can really cover the ground."

Cardoon -- "like artichokes on steroids" -- can be a vegetable gone wild.

"Four seedlings turned into more than 200 plants," Shor said. "They're pretty but very invasive by seed. My removal technique consisted of three teenage boys, each with two machetes. The seedlings persisted for two to three years and were dispatched immediately with a shovel."

Bee balm is another herbal thug.

"If you really like to divide plants and share them with others, you can grow bee balm," said Judy McClure, coordinator for the Sacramento County University of California Cooperative Extension master gardeners. "But if not, it's incredibly invasive."

Master-gardener hotlines get lots of calls about controlling invasive plants, especially in spring when new seedlings grow like crazy.

"Vinca major and blackberries are always problems," McClure said.

So is Bermuda grass: "You always have roots left no matter how much you dig," Zagory said.

According to University of California Master Gardener Bill Pierce, the false strawberry (Duchesnea indica) -- a cute ground cover with little yellow flowers and berrylike fruit -- has many Sacramento gardeners pulling their hair out as it rapidly invades lawns and flower beds. Instead, concentrate on pulling out the runners.

"They're pretty shallow-rooted," McClure said. "You've got to be diligent."

Several of these thugs had been recommended for low-water, low-maintenance gardens.

"In particular, there's a lot of concern over Mexican feather grass (Nassella tenuissima or Stipa tenuissima)," McClure said. "It's now considered an invasive plant (and a danger to wildlife areas)."

Pampas grass also falls in that category; its feathers broadcast seed everywhere.

With its pretty pink blooms, Mexican evening primrose became an instant hit in low-water gardens.

"It's so beautiful, so tough and doesn't need any water," Zagory said. "But if you put it where it has water, it will take over the whole yard."

California fuchsia is another low-water native that rapidly expands with regular irrigation.

"It will overtake anything shorter," Zagory said.

Lantana -- usually a low-growing, colorful shrub - will do the same thing, swallowing its neighbors if given too much water.

Native roses -- the California wild rose (Rosa californica), in particular -- spreads rapidly via its roots.

Santa Barbara daisy -- an UC Davis Arboretum All-Star -- also can go out of control if overwatered.

"People plant natives for low-water use," noted McClure, "but are still watering too much."

Blooming bulbs or corms can delight hummingbirds and offer loads of cut flowers. But alstroemeria -- the Peruvian lily -- multiplies like crazy.

"Their spreading ability makes people very unhappy," Zagory said.

Arum lily, commonly called white calla lily, has a similar growth habit.

"If you plant one, it's for life," Coulat said. "I finally had to sift all of my soil. That was the only way I was going to get rid of it."

Vines are notorious stranglers. They're popular because they grow fast and thugs for the same reason.

Ivy -- particularly the English or large-leaf Algerian varieties -- are infamous for their ability to fill a large garden bed, then climb house walls and strip off paint. Ivy can pry apart fences with its powerful growth.

"It looks beautiful in the landscape, but it's high-maintenance," McClure said. "If you let it go, it's a nightmare."

Japanese honeysuckle, too, can quickly leap its boundaries to climb anywhere. So can creeping fig (Ficus repens) and wire vine (Muehlenbeckia). Kudzu -- another Asian ornamental that went wild -- is outlawed in several states.

Fast-growing Himalayan blackberry threatens habitat and crowds out other plants -- including native blackberries.

Blue Dawn morning glory reseeds so prolifically, it comes back year after year -- like it or not.

Pink jasmine (Jasmine polyanthum) has a beautiful scent and charming flowers, but look out. Said Zagory, "I saw it coming out of the eaves of my roof! It got inside my walls."

"The shoots just take off," Shor said. "It roots as it goes. It's a shame. It's so pretty. You wait to pull it out because it's in bloom. But you'll really regret it later."

(Email Debbie Arrington at darrington@sacbee.com.)
 

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