But with the mail one spring morning came a letter from “noxious weed specialist” Karen Peterson of the King County Noxious Weed Control Program, informing me that she had identified an outbreak of garlic mustard—apparently the new “it” invasive in the Northwest—on my property. Her letter went on to say that I was obliged by state law to control this fast-growing weed. Peterson and her fellow control specialists spend most of the spring and summer driving around King County looking for outbreaks of garlic mustard and other invasives classified by the state as “Class A” noxious weeds—nonnative plants that are dangerous to humans, animals, private and public lands, and native habitats, and which property owners are required by law to eradicate. Fail to do so and you may find your weeds removed for you, by King County, and getting billed for costs plus fees.

“The reason we are so aggressive about this weed is because it poses a serious threat to natural areas,” Peterson wrote. “It not only flourishes in the shade, where many of our native plants and animals reside, but it inhibits nutrient uptake of other, desirable plants and disturbs the life cycles of a variety of other organisms,” including trillium bleeding heart, piggyback plant and woodland violet.

In response, I called Peterson, and she offered to come out and show me exactly what garlic mustard looks like, where I could find it on my land and how to remove it. A few days later, she gave me a tour of the flora of my property, pointing out which plants were native, and which nonnatives—including copious stands of garlic mustard—should be removed. (Any King County resident can get Peterson or another “control specialist” to come by for a similar walk-around; the program is funded by a $2.10 charge on all county property-tax assessments.)

Garlic mustard, a biennial herb native to Europe, was introduced in North America for culinary reasons—it has been harvested for centuries by cooks looking to add a little extra kick to their soups, salads and other dishes. By escaping into the New World, the plant found itself with lots of prime terrain to colonize and none of the predators—such as weevils—that it had to contend with back home.

As a result, it didn’t take long for garlic mustard, which thrives in shady, mild and moist environments, to hopscotch its way up and down the Eastern Seaboard and then westward. Indeed, western Washington, with its omnipresent tree canopy and mild, drizzly weather, makes a fine habitat for the plant.

This article originally appeared in the August 2012 issue of Seattle magazine.