Black knapweed, a regulated Class B noxious weed, is a perennial found in meadows, pastures, and open areas. Upright, branched stems with short hairs grow 1-5 feet tall. Basal leaves are narrow, widest at their base or middle, with leaf stalks; stem leaves are smaller, even narrower, and stalkless. In summer-fall, purple flower heads appear at stem ends. Bracts at base of flower head have dark brown or black fringed margins. Reproduces by seed.   

Legal Status in King County, Washington

Public and private landowners are required to control infestations of black knapweed on their property in King County, Washington. Black knapweed is a Class B Noxious Weed in Washington, first listed before 1988. It is designated for required control by the Washington State Noxious Weed Control Board and is on the list of Regulated Class B Noxious Weeds in King County. For more information, see Noxious weed lists and laws or visit the website of the Washington State Noxious Weed Control Board.

Additional information on black knapweed

• Washington State Noxious Weed Board (external link)
• Selected Knapweeds of Washington is a an informative color brochure describing knapweeds. (316 KB Acrobat file).

What to do if you find this plant in King County, Washington

Please notify us if you see black knapweed growing in King County. Our program staff can provide the property owner or appropriate public agency with site-specific advice on how best to remove it. Also, because black knapweed is still found in only a few places in the county, we have an opportunity to stop it from spreading if we act quickly. We map all known locations of regulated noxious weeds such as black knapweed in order to help us and others locate new infestations in time to control them.

Black knapweed photos

Report black knapweed in King County, Washington

• Please notify us through our online infestation form

Locate black knapweed in King County, Washington

• Use our interactive noxious weed map and search for black knapweed

Related information

• Agriculture in King County, Washington
• Northwest yard and garden
• Animals, plants and habitat

Related agencies

• Dept. of Natural Resources and Parks
• Water and Land Resources Division

Program offices are located at 201 S. Jackson St., Suite 600, Seattle, WA 98104. To contact staff, see the Noxious Weed Control Program Directory, send an email, or call 206-477-WEED (206-477-9333).