The 2023 King County Noxious Weed List is Official!


What does it mean to be a noxious weed?

First things first, what is a noxious weed? And why do we care? “Noxious weed” is a legal designation. To become a noxious weed a plant must meet 4 criteria. 

  1. Introduced to Washington state 
  2. Spread beyond where they are planted
  3. Create harm (ecological, environmental, or social)
  4. Difficult to control

This harm can be agricultural, such as reducing crop output, ecological, such as out competing our native plants, or physical, such as toxic to humans or livestock. They can impact wildlife, human health, land value, recreation, and natural resources. Chances are several of those are relevant to your life! 

The state Noxious Weed Control Board decides which plants are noxious. They also decide where they should be controlled based on how widespread they are. County Noxious Weed Boards can select additional species to educate about on a more local level, but do not have the power to select weeds for designated control without state approval (more on this below). 

With the help of our awesome seasonal field assistants like Mario pictured here, the King County Noxious Weed Control Program surveyed more than 10,000 sites in 2022!

2023 list updates

Designation changes

There were no new additions this year to the state noxious weed list. But there were some designation changes. When weeds are “designated” on the state list, counties are required to list them as regulated (required for landowner control) on their county level weed list. That is, unless the counties make an official request to “un-designate” a particular weed within their county lines. 

One went into effect per the request of the King County noxious weed control program:

shiny geranium (Geranium lucidum) was changed to non-designate in King County. This means it is no longer required for control (within the boundaries of King County) by the state. We have elected to require control of shiny geranium at or above 1000 feet in elevation throughout King County. We are requiring this because recent studies have indicated that higher climates will become a more suitable habitat for shiny geranium due to climate change.

This was due to shiny geranium no longer meeting the legal definition for a Class B designate in King County, which is: a weed whose population in a region or area is such that all seed production can be prevented in a calendar year. 

More information can be seen on the Washington State Noxious Weed Control Board’s website.

New additions

Weeds of concern are weeds that have not gone through the legal process of becoming a noxious weed, but are considered to be a concern on the county level. Weeds are added to this list if there is reason to believe that the selected species has potential to behave as a noxious weed. This decision is made official by the county’s noxious weed control board, versus the state’s. 

Norway maple; harlequin maple

(Acer platanoides) is currently on the Monitor List for the state and was added as a weed of concern in King County. Norway maple was planted all over Washington. It is an excellent street tree due to its dense shade and ability to grow in all sorts of conditions from deep shade forests to urban heat sinks. However, that same adaptability and no natural competition means it is out competing our native plants. Its dense canopy reduces suitable habitat for many species. Also, its shallow root system makes difficult growing conditions for native understory shrubs and herbaceous species. In an urban environment these root systems can damage infrastructure. There is about a 25-year lag time in maturity for Norway maples, so they can appear relatively harmless in the environment for a while and then suddenly disperse winged seeds to the wind that spread readily and germinate quickly. 

Introduced peavines

Narrow-leaved perrenial peavine (Lathyrus sylvestris) and broad-leaved perennial peavine (Lathyrus latifolius)

Left: Broad-leaved perennial peavine
Right: narrow-leaved perennial peavine

These introduced peavines were added as a weed of concern by the request of a GSP Forest Steward who wanted to help educate the public about the weedy nature of this plant. These plants are present in King County in parks, restoration areas, and long roadsides and right of ways. They can be toxic to humans and livestock if consumed in large enough quantities. The broad-leave perennial peavine is also on the state Monitor List.  

Both these listings will help educate landowners, gardeners, arborists, and recreational users about impacts and pathways of spread. 

Common name changes

We changed the common name of one plant this year. English holly (Ilex aquifolium) is now common holly. This change is part of an ongoing effort to remove location based and nationalist names for plants in favor of descriptive ones. Check out our 2022 weed list update blog post for the 9 common name changes that were made for the 2022 list and the previous year’s for the 6 common name changes made for the 2021 list. 

Common holly was proposed to be added to the 2023 list as a Class C noxious weed by a community member from Whatcom County, ultimately the proposal did not pass. Washington Native Plant Society has a write up on the vote by King County Noxious Weed Board Chair, Becky Cheney, in their Winter 2022 issue of Douglasia.  

For more information on the history of common holly in Washington state check out a recent blog post: The story of English holly in Washington – Noxious Weeds Blog ( 

For more information about any of the mentioned weeds, find their detail pages on our King County Noxious Weeds website or on the Washington State Noxious Weed Board website. 

Last year’s changes maintained

Changes made to last year’s list were maintained this year. To see last year’s changes, visit our blog post on the 2022 list update: The 2022 King County Noxious Weed List is official! – Noxious Weeds Blog (