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Originally published Thursday, July 29, 2010 at 10:00 PM

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EcoConsumer

Root out trouble: Noxious weeds grow quickly, choke out native plants

Philosophically, weeds have a certain appeal. "A weed is just a flower in the wrong place," as the saying goes. We can think of weeds as misunderstood, resourceful outcasts searching for a home. But in the real world, some plants in the wrong place cause serious harm. Governments classify these plants as noxious weeds and mount extensive programs to keep them at bay.

Special to The Seattle Times

Philosophically, weeds have a certain appeal. "A weed is just a flower in the wrong place," as the saying goes. We can think of weeds as misunderstood, resourceful outcasts searching for a home.

But in the real world, some plants in the wrong place cause serious harm. Governments classify these plants as noxious weeds and mount extensive programs to keep them at bay.

Q: "Noxious weeds" sounds almost comical. What does that mean, and are they really that much of a problem?

A: That name does elicit some grins, and there was even a Seattle rock band called Noxious Weed Inspector. But this under-the-radar issue has major environmental, economic and health implications.

Noxious weeds are invasive, nonnative plants that are highly destructive and often difficult to control. Most grow quickly and choke out native plants and other desirable vegetation, and some are poisonous to humans and livestock.

Q: Which weeds pose the biggest problems locally?

A: It's a long list, but King County noxious-weed expert Sasha Shaw names five you should know about:

Invasive knotweed: Three closely related species of invasive knotweeds, commonly found near water, have also become widespread on roadsides and in backyards. Very difficult to eradicate, this bamboolike plant has young shoots that look like asparagus. Shaw says several new homeowners in King County have recently experienced severe knotweed infestations, possibly because the developer failed to control the plant when clearing the land.

Tansy ragwort: Toxic to horses and cattle, tansy ragwort has spread throughout the Northwest. It can be tough to identify, and control measures such as mowing can make the problem worse if not done at the proper time.

Giant hogweed: Growing up to 15 feet tall, this weed looks like the wildflower Queen Anne's lace "on steroids," says Shaw. This is a perfect example of why you should never touch any weed you don't know, since the sap from giant hogweed causes painful blisters. Children using its stem as a spy scope have burned their faces.

Poison hemlock: As with many other weeds, poison hemlock can easily be confused with edible plants. The death of a Tacoma woman in April has been attributed to eating this weed in a salad.

Garlic mustard: This fast-spreading plant can take over the understory of a forest and has become a problem in several Seattle parks and Bellevue's Coal Creek Natural Area.

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Q: Those all sound nasty. How do I control them or other noxious weeds?

A: Each weed needs to be handled differently. Fortunately, many useful resources now exist, especially on the Internet, to help you identify and deal with noxious weeds.

King County's Noxious Weed Control Program (www.kingcounty.gov/weeds or 206-296-0290) offers great weed photos and a wealth of information. Other counties also have weed programs, or visit the state Noxious Weed Control Board website at www.nwcb.wa.gov. Control of certain problem weeds is required by law.

Q: What about English ivy?

A: Planted extensively in the Seattle area for decades, several varieties of English ivy are now classified as noxious weeds. If your ivy makes berries, cut those off and put them in your yard-waste-collection container (not a backyard composting bin) to prevent them from being spread by birds. Don't let ivy climb your trees, since it makes trees heavier, less healthy and more likely to blow down.

Q: I love the way ivy looks in my yard, and the same goes for my gorgeous butterfly bush. Do I really have to get rid of those?

A: If you grow invasive weeds such as English ivy or butterfly bush as ornamentals, make sure they don't spread elsewhere. Cut off the spent flower heads from your butterfly bush in the fall.

Just because weeds are flowers doesn't make them any less noxious. "It's not just about what's pretty to you," says Shaw. "You have to look at the bigger picture."

Tom Watson is project manager for King County's Recycling and Environmental Services.

Reach him at tom.watson@kingcounty.gov, 206-296-4481 or www.KCecoconsumer.com

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