If you’ve ever wondered what makes a plant a “noxious weed,” here’s the quick scoop:
Noxious weeds are plants that:
- Are not native to Washington.
- Spread aggressively beyond where they were planted.
- Cause harm (to crops, native plants, animals, or even people).
- Are difficult to control once they get established.
These weeds aren’t just “annoying.” They can lower property value, damage forests, harm wildlife, and even pose risks to human or animal health. That’s why Washington State law requires certain weeds to be controlled or removed.
👉 In King County, our Noxious Weed Program helps homeowners and land managers with free advice and technical support.
What’s New for 2025?
Three plants have been added to King County’s official weed list this year:
1. Common Holly (Ilex aquifolium) – Class C (Non-Regulated)
- Status: Widespread; control is encouraged but not required.
- Why it matters:
- Shades out native plants in forests.
- Slows growth of nearby trees.
- Highly flammable—can increase wildfire risk.
- Homeowner takeaway: If you have holly on your property, consider removing it, especially near natural areas or forests.
2. Roundleaf Bittersweet (Celastrus orbiculatus) – Class A (Regulated)
- Status: Rare in Washington (only 4 known sites statewide). Control is legally required.
- Why it matters:
- Woody vine that can climb over 100 feet.
- Twists around trees, adding weight and sometimes killing them.
- Known invasive in the Eastern U.S., New Zealand, and Europe.
- How to spot it:
- Loses leaves in winter.
- Bright orange-red berries with yellow shells hang on through winter.
- Homeowner takeaway: If you see it, report immediately. Early detection is critical.
3. Marsh Thistle (Cirsium palustre) – Class A (Regulated)
- Status: Not yet in King County; only 1 known infestation in Washington (Spokane). Control is legally required.
- Why it matters:
- Grows in wetlands and marshes, outcompeting native wetland plants.
- Can spread into farmland and impact forage for livestock.
- Related to the more common creeping thistle.
- How to spot it:
- Biennial plant (2-year lifecycle).
- Produces clusters of bright magenta flowers in its second year.
- Homeowner takeaway: Not common here yet, but keep an eye out in wet areas. Report if found.
👀 Why Should Seattle Homeowners Care?
- Noxious weeds spread from just one plant.
- They harm the natural beauty and health of our forests, wetlands, and backyards.
- Some species are legally required to be removed—ignoring them can result in fines.
📢 What To Do If You Find a Noxious Weed
- In King County: Email a clear photo and nearest address to noxious.weeds@kingcounty.gov.
- Elsewhere in Washington: Contact your county weed board.
- Not in WA? Search “[your state] noxious weeds” to find local resources.
Looking Ahead to 2026
The state weed board is already reviewing plants for next year’s list. If you’re interested in being part of the process, check out the Noxious Weeds & Prohibited Plants Guide on kingcountyweeds.com.
✨ Bottom line for homeowners: Know what’s growing on your property. Some “pretty plants” can be harmful invaders. With quick action, we can stop new weeds before they spread.
