This Class B noxious weed is found throughout the State of Washington and control is required in King County. Purple loosestrife is sometimes sold as a garden ornamental. This plant is on the quarantine list (144 KB Acrobat file, 21 seconds on 56K modem), and it is illegal to buy, sell, transport or offer this plant for sale in the state of Washington.

The flowers are magenta, and they are found on long spikes from July to October. Purple loosestrife has square stems, which help to tell it apart from some of the look-alikes that grow in the same areas. In winter months, dead brown flower stalks remain with old seed capsules visible on the tips. Loosestrife's appearance is similar to fireweed and spirea and often co-habitates with garden loosestrife.

Purple loosestrife is a long-lived perennial that can reach over 9 feet tall. Some plants can produce over 2 million seeds the size of ground pepper. This plant spreads by seed and root fragmentation. Purple loosestrife is native to Europe and Asia, and was initially introduced to the northeastern seaboard of the United States in the ballast of ships in the 1800's. It has been repeatedly and continually introduced as a garden plant. Because of the impacts to fresh and brackish wetlands across the nation, purple loosestife is targeted for control and is found on states noxious weed lists.

There is an active and effective biological control program in use against purple loosestrife in Washington State and in King County.

Purple loosestrife photos - click thumbnail for larger image

If you find purple loosestrife in King County, please notify us through our online infestation form.

To find out where we have records of this weed in King County, use our interactive noxious weed map and search for purple loosestrife.

For more information on identification and control of purple loosestrife, please read the Purple Loosestrife Weed Alert (1.01 MB Acrobat file)

For detailed information on controlling purple loosestrife in King County, please read the purple loosestrife best management practices (201 KB Acrobat file).

For additional background information on purple loosestrife, please follow this link to the WA State Noxious Weed Control Board.