Beware Of The Aggressive Plant

 By Jane Berger

Associated Press

Beware plant geeks bearing gifts. They may be bearing enemies instead of friends.

I learned my lesson the hard way, from a true plant geek who lived next door. Hubert’s garden was filled with varieties he came to know in his native Britain, hunted down from obscure sources all over the United States, and then ordered by mail. He also loved to propagate plants and share them with friends and neighbors.

I had no problem with the espaliered fig tree and the towering pink crape myrtle he gave me, but I rue the day he came trotting over with a little piece of “extra” spurge that he was certain I would love to have in my garden.

I was not familiar with this particular euphorbia, but then, Hubert had hundreds of plants in his garden that even avid American gardeners would never know.

I planted it in the herb garden, hoping it would help fill in some of the empty space between the sage and the chervil. And did it ever! Within a few years, it had carpeted the herb garden, jumped across the path to a perennial bed, and popped up several yards away under the dwarf nectarine tree. Even after the garden was completely renovated, the spurge sporadically appeared in the middle of the new lawn.

Hubert was not sure of the botanical name of this euphorbia, but it turned out to be Cypress spurge (euphorbia cyparissias), a European immigrant that is now considered invasive in many states. It is a beautiful plant, with soft green needle-like foliage –– you would almost think it was some kind of a dwarf evergreen –– and in summer it has small yellowish-green bracts that later on turn to a reddish hue. I hate to say it, but I actually would plant this euphorbia again, but only in an area between two slabs of concrete or in a container.

Another well-intentioned friend gave me the rapacious lemon balm (melissa officinalis) and the tenacious tansy (tanacetum vulgare), which she insisted that I try because of its quaint old reputation as the “strewing herb” –– strewn about the ground in olden times to disguise repulsive odors. I think it is known as the “strewing herb” because it strews its seeds all over the yard.

The lemon balm has a pleasant, lemony smell, but it is a lemon of a plant. It, too, is coming up all over my yard, and although its leaves can be used for a delightful tea, I have so much of it I could almost go into the herbal tea business.

Plant catalogs and nurseries almost never warn you that a plant might be problematical. One prominent mail-order house notes that tansy leaves can be used as an insect repellent, and another observes that the obedient plant (physostegia virginiana) gets its name from the ability of the blooms to stay put if pushed around the stem. It will not stay put in the garden, however, unless you buy the cultivar Miss Manners, which is far better behaved than its aggressive cousins.

Most nurseries and growers are in the business of selling plants, and they tend to emphasize desirable, rather than undesirable, plant traits. Before you plant anything, you should obtain a copy of the “invasives” list that is kept by your local county extension agent, or check out individual plants in reference books or on the Internet.

Not all aggressive plants are necessarily problematical. Part of it depends on the kind of look you want your garden to have.

Philip McClain, a landscape designer in Washington, D.C., welcomes a number of plants that seed themselves around his expansive yard. “How do you tie your garden together,” he said, “unless you do it with plants like forget-me-not, creeping phlox, or even Siberian bugloss.” Mr McClain uses these spring spreaders as a carpet under many different kinds of spring-flowering bulbs.

Mr McClain even uses the despised goldmoss stonecrop (sedum acre), which he notes that many gardeners would prefer to pull and then burn to a crisp.

Someone gave him a handful of it several years ago, and he loves its effects in the garden. “It’s great creeping in among the stones,” he said, “and besides giving you mustard yellow flowers in spring, it’s got a tight evergreen presence in winter.” After it blooms, Mr McClain “pulls it up by the handfuls” and throws it away –– and that keeps it well under control in his one-third-acre urban garden.

In early spring, Mr McClain favors nodding star-of-Bethehem (ornithogalum nutans), which colonizes readily and becomes more prolific every year. Mr McClain likes it because of its fragrance, its use as a cut flower, and because “the first big blast of heat every year knocks it out.” He overplants it with perennials and uses it under deciduous flowering shrubs such as viburnums and azaleas.

In late summer, Mr McClain loves the look of cardinal flower (lobelia cardinalis), which blooms after many other flowers have faded. He lets it grow up in between the stones on his patio where he can appreciate its spiky look from inside the house “when the mosquitoes have the rule of the garden.” He lets the seed heads dry on the plant, then shakes them around other parts of the garden where he would like to have them the following year.

Mr McClain believes that a lot of plant lovers simply fail to appreciate a plant’s particular attributes, even if it is extremely vigorous. “I’d like to educate the public,” he said, “to relax and focus on the next crop of beauty. Sedum can be an aggressor, bar none, but if you have a lot of other things going on, it’s not a problem.”

Mr McClain said he does confine some plants such as euphorbia and plumbago to containers, but he said “there are very few plants that I don’t like.” If you should acquire an unruly plant from a friend, he recommends that you just “plant another aggressor next to it and let them duke it out.”