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Noxious weeds

King County, Washington

To offer a suggestion or report an error on the King County Noxious Weeds website, please contact Sasha Shaw, education specialist.

Common St. Johnswort
Hypericum perforatum

st. johnswort flowersThis species should not be confused with the ornamental St. Johnswort found in gardens. Common St. Johnswort is taller and less dense, with smaller flowers. Usually found along roadsides and in empty lots in western Washington, this weedy species can also be found in natural areas. In eastern Washington and in other regions of the western United States, common St. Johnswort is widespread and difficult to control.

Legal status in King County, Washington

Common St. Johnswort is a Class C noxious weed on the Washington State Noxious Weed List. It is on the Non-Regulated Noxious Weed List for King County, Washington. Control of Common St. Johnswort in King County is recommended but not required. Common St. Johnswort is not on the prohibited plants list administered by the Washington State Department of Agriculture, but some nurseries have volunteered to stop selling it due to its danger to natural resources.

The King County Noxious Weed Control Board encourages property owners to remove Common St. Johnswort where possible and to avoid introducing it to new landscapes. Ornamental plantings can be contained by removing flower stalks before they form seeds.

Additional information on common St. Johnswort

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

Because Common St. Johnswort is so widespread, property owners in King County are not required to control it and we are not generally tracking infestations. We can provide advice on how to control Common St. Johnswort, but there is generally no legal requirement to do so.

Common St. Johnswort photos - click thumbnail for larger image

st. johnswort leaves - click for larger image st. johnswort plant - click for larger image st. johnswort biocontrol - click for larger image

Related information

Related agencies


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).