I used to think a weed was merely a plant in the wrong place. This is still true in many cases, as when my favorite forget-me-nots become the very same bullies colonizing my borders. Some weeds, however, are so opportunistic as to become noxious. And now that kudzu, the King Kong of invaders, has been sighted for the first time in our state (in September, near Vancouver) maybe we all need to pay closer attention to a plant's tendency to spread where it isn't wanted.

We've felt safe from the curse of kudzu in this corner of the country, believing it required more warmth than our climate offers. Climatic change is upon us, however, and a plant can become established in even a year or two of unusually wet summers and warm winters, explains UW assistant professor Sarah Reichard, an expert on invasive plants. She says any plant that vigorously self-sows has the potential for invasiveness, and worries about such popular garden plants as Verbena bonariensis and Himalayan honeysuckle (Leycesteria formosa).

Reichard did have some good news about ivy, though. Because shade-tolerant English ivy is blanketing our parks and natural areas, smothering out biodiversity, we've been advised (OK, harangued) that it is irresponsible to grow any kind of ivy. Not necessarily true, says Reichard. The smaller and more variegated the leaf, the less invasive the ivy. In fact, only four types of ivy are on the Washington State Noxious Weed List: Hedera hibernica 'Hibernica,' H. helix 'Baltica,' 'Pittsburgh' and 'Star.' They are all on the lowest rung of the bad-plant ladder, type "C," which is an advisory warning. The most dangerous weeds are in class "A," where control is required by law.

The state defines noxious weeds as non-native plants that are aggressive, competitive and highly destructive. They usually lack natural enemies and resist control. Many have escaped from gardens to destroy natural plant and animal habitat. King County has 33 weeds on its "A" list, including rogues such as Himalayan blackberry, giant hogweed and purple loosestrife, but also some unexpected plants such as two types of toadflax and one artemisia.

This state definition seems to focus on the nursery industry, claiming all weeds are exotic (meaning they've been imported) and have escaped from gardens. But how about our native weeds like bracken, rush, horsetail and even mosses that grow in the lawn? They, too, are thugs adept at out-competing more desirable plants. Considering that the joy of gardening in our hospitable climate is the ability to grow a wide variety of species and that gardeners get a thrill out of new and unusual plants, what is a responsible gardener to do?

First, buy plants from nurseries and catalogs you trust. And it helps to recognize the enemy. The Seattle Tilth Demonstration Garden (4649 Sunnyside Ave. N., 206-633-0451) has a weed display with labeled specimens of dozens of different species. To help gardeners keep up on what plants are problematic in our area, the King County Noxious Weed Control Program's Web page has lists of the worst weeds: dnr.metrokc.gov/wlr/lands/weeds/index.htm. If such a long URL drives you crazy, just call the local office at 206-205-6927. The state puts out a booklet with photos of noxious weeds, rather quixotically arranged by color, so if you have a yellow or even pink invader, it's easy to identify. Order a free copy of "Selected Noxious Weeds of Washington State" by writing to the State Weed Control Board, P.O. Box 42560, Olympia, WA 98504-2560.

It is a little scary to read about these unruly plants. But if we want to be stewards of the environment while continuing to have access to new and exciting plants, we'll have to work at striking the balance.

Now In Bloom

Pink daffodils add an unexpected note to the spring landscape. Narcissus 'Accent' has a salmon-pink frilly center cup surrounded by creamy white petals. It grows 16 inches high, is a reliable naturalizer, and pairs beautifully with blue corydalis, chartreuse lady's mantle, or the spotted leaves and pastel flowers of pulmonaria.

Valerie Easton is manager at The Miller Horticultural Library. Her new book, "Plant Life: Growing a Garden in the Pacific Northwest" (Sasquatch Books, 2002) is an updated selection of her magazine columns. Her e-mail address is vjeaston@aol.com