- The Washington Times - Tuesday, July 18, 2000

Ironically, plants you have loved and nurtured can turn on you. But it isn't their fault. It's yours.

You chose the wrong plant for the site and now it is taking over your garden, strangling the perennials and choking out the flowering shrubs.

What to do? You must heartlessly rip out that plant you once nurtured and redesign your gardens. This is known as learning about invasive plants the hard way. All the best gardeners have done it. These plants look innocent sitting there on display in a garden center. They are described in glowing terms in mail-order catalogs. And there are indeed excellent uses for them just not in your average residential garden.

Some invasive plants you might encounter:

• The granddaddy of all invasive plants has to be bamboo, which will take over everything in its path except maybe a large body of water. Even concrete will not stop common bamboo unless it is deep concrete. Bamboo in a side yard has been known to come up through the concrete floor of an adjacent garage. It has come up through a concrete runway at New York's La Guardia Airport.

Because bamboo also is one of the loveliest of rustling grassy plants, growers of ornamental grasses have cultivated new kinds of clumping bamboo that do not spread rampantly. Of course, if you have ever had to hack down and remove invasive bamboo, you probably will not be in a hurry to plant any variety of bamboo any time soon, but keep an open mind. Just be careful in selecting a variety that isn't invasive. These include the Fargesia varieties, two of which are umbrella bamboo and fountain bamboo.

• The perennial monarda, also known as bee balm, has more than a half-dozen varieties with pretty summer flowers in a range of colors that attract hummingbirds and look to be an asset to any sunny perennial garden. Be careful where you plant them. In a cottage garden of gentler perennials, monarda can turn into a space hog. It probably is best used in a mass by itself. This is generally true of almost all invasive plants.

The way you might tell ahead of time if you are selecting an invasive plant is by reading carefully the description in a catalog or on the plant tag in a garden center. The word "vigorous" is one giveaway. It is sort of a code word for gardeners.

I looked up monarda in the Wayside Gardens retail catalog, which lists six varieties, and in the Babikow Greenhouses wholesale catalog, which lists 10 varieties. Each lists the variety "Jacob Cline," a lovely plant with rich, red flowers. Wayside, which is based in South Carolina, calls it not vigorous, but "an exceptionally sturdy grower." Babikow, which is in Baltimore, calls it "a vigorous plant."

• Another pretty flowering plant that is innocent looking but ruthless when it comes to strangling neighboring plants is hypericum, commonly known as St. John's Wort. Wayside describes it this way: "This fast-forming shrub forms a thick carpet in one season, its 3-inch golden flowers blooming all summer. Plants grow 12 to 18 inches high and 18 to 24 inches wide." The tip-off here is "fast-growing," but even if that isn't warning enough, it's better than Babikow's description, which is simply, "Large yellow flowers with showy stamens."

Babikow's catalog is written for professionals, however, who know the assets and liabilities of hypericum. Its greatest asset is as a low-maintenance ground cover where erosion control is necessary or where it might take abuse, such as between a sidewalk and the street. It survives sweltering sun and drought, and is semi-evergreen in the Washington area with purplish foliage during at least part of the winter.

• Another invasive ground cover used effectively for erosion control is wintercreeper euonymus, usually in a shadier situation. In a residential garden, it will cheerfully choke out ornamental shrubs. On a bank that threatens to erode, however, it makes a nice, tough green cover as long as there is nothing planted in its path.

• Houttuynia is another deceptively pretty plant with heart-shaped red, cream and green foliage and small white flowers in June. It is invasive in that it spreads like a weed although it doesn't really strangle other plants. About 12 inches tall, it just overtakes everything, coming up in, around and through other plants.

Babikow sends a clear message about this one, saying, "Grows vigorously in moisture-retentive soil, spreading by underground stems." The plant does have good points it is relatively easy to pull out where it isn't wanted, and, because it has a mildly unpleasant aroma when disturbed, deer don't bother it. On the other hand, it is an unsightly mess of broken twigs all winter if you don't clear it out, and then it is late to leaf out in the spring.

• Another ground cover you must watch out for is aegopodium, commonly called bishop's weed. It is usually sold in a variegated variety with foliage that will brighten a shady spot but also thrive in the sun. It has white flowers in late spring or early summer. Wayside gives you the code word "Extremely vigorous." Babikow says, "Vigorous ground cover." While aegopodium will survive poor soil and is good for problem areas, it also is a favorite food of deer.

• One of the most useful invasive plants under certain conditions is liriope spicata, which will survive dry shade and is as deer-proof a plant as you'll find. It is most effective in a natural rather than formal garden, forming a dense evergreen border that weeps over the edge of the lawn, eliminating the need for edging and mulching.

This, however, is not the liriope most professionals favor, known as Liriope muscari, "Big Blue." While both have grassy foliage and flower stalks, "Big Blue" has prettier flowers than spicata and grows in a clumping rather than spreading form. In most situations, it is preferable to spicata, but deer will eat it.

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