Thornton Creek Noxious Weed Knockout Project

Forterra works with residents, local organizations, and local governments to manage aggressive noxious weeds like knotweed in Seattle's largest watershed, the Thornton Creek basin.

Live on Thornton Creek?

Because noxious weeds can spread so easily, participation from all landowners is essential for effective control. Forterra is recruiting landowners who live on or near Thornton Creek and its tributaries to sign up for our program. We will survey, treat, and monitor knotweed and other noxious weeds on your property at no cost to you. We are currently focusing on properties upstream from Meadowbrook Pond to participate in our program.

Click here to sign up for our program!

By participating in this program, you’re contributing to a landscape-scale effort to improve water quality and restore salmon habitat in your watershed. You’re also preventing damage to your property and septic systems, and our community’s roads. Healthy watersheds require every landowner to be a steward of their environment, so we thank you for your participation! Email us at if you have any questions.

Noxious Weed Control on Thornton Creek

In fall of 2017, the Thornton Creek Alliance and partners King County, City of Seattle, the City of Shoreline, Earthcorps, and Forterra, convened for the first time to discuss a coordinated effort to control noxious weeds (mainly knotweed, but also policemans helmet, garlic mustard, shiny geranium, and giant hogweed) in the Thornton Creek Watershed. In March 2018, the parties completed a strategic plan to guide these efforts. Thornton Creek Alliance led the charge in mapping knotweed and other noxious weeds in the watershed.

Thornton Creek Weed Mapping

In 2019, Forterra began surveying for noxious weeds along Thornton Creek, and began treating treatments in 2020. The ultimate program goal is to work with Thornton Creek residents to control invasive weeds and restore healthy streamside forests. This work is made possible by funding from King County’s Waterworks program.

What is knotweed and why control it?

Knotweed (Polygonum spp.) is a bamboo-like, non-native plant that wreaks havoc on properties and ecosystems. Once established, knotweed forms dense stands that crowd out native vegetation and clog small waterways, increasing bank erosion and lowering the quality of riparian habitat for fish and wildlife.

Knotweed spreads rapidly and is remarkably difficult to remove. Winter floods and beaver activity can bring knotweed to your property, so even if you haven’t seen it before, you may have a new infestation on your property.

Learn More – King County Noxious Weeds