Weedy Fall Activities

As we shift into fall you may be thinking it’s time to take a break from all the weed control of summer. While you should certainly take your well-deserved rest, fall is a great time for ongoing maintenance.  Between small fragments getting left behind and seeds remaining in the soil (some plant’s seeds can survive in the soil for decades!!) these weedy little plants are going to stick around for a while. But mulching a recently cleared area, replanting it, and keeping an eye out for resprouts will go a long way in reducing the amount of regrowth next year. Weed control is a marathon not a sprint. Keep it slow and steady and you’ll have a wonderfully healthy habitat to enjoy for years to come. 

Fall Weeds

If all you really want to do is pull weeds, you’re in luck. The wonderful rainy season of the Pacific Northwest makes for soft soils and easier weed removal.  For more detailed information see our resources section at the end of this blog.

Younger woody plants like common holly, cherry laurel, blackberry, English ivy, butterfly bush, Scotch broom etc. can all be pulled or dug out while the soils are moist. If you time it right with the rain, cut-treat, and lancing with herbicide can also still be effective for all growth stages. Check out our Best Management Practices for more details. If you absolutely cannot get to digging or herbicide, cutting off the flowers and seed heads is one step in minimizing seed spread. It’s best to dispose of flowering and seeding parts in the garbage (compost does not get hot enough to kill seeds).

Click on a photo above and then click the info icon to learn more about the woody species!

Cut-treat method for woody plants:

Step 1: Cut down the woody stem to about an inch above the soil.

Step 2: Apply concentrated (50-100%) herbicide on the freshly cut stem.

New plants are called “seedlings”. Some of these grow into rosettes – early growth stages for certain species where leaves grow in a circular/low growing arrangement.

Rosettes typically start to form in fall, lie dormant in winter, then grow again in spring. With the first fall rains, keep an eye out for garlic mustard, poison hemlock, thistle, and tansy ragwort rosettes. If you know you have an infestation, watch out for seedlings and rosettes and yank them out before they get too big (try to get as much of the root as you can!). 

Click on a photo above and then click the info icon to learn more about the rosette forming species!

The window is closing on knotweed control for the year! Check out our videos and if you have any knotweed growing on your property you can borrow an injector to control them. The best time to inject your knotweed is in late summer to early fall. The plants need to be big enough to hold the herbicide in their hollow stems (about the size of your pinky finger and larger). Late in the season knotweed stems get very woody and hard to inject, although foliar application (spraying) is still possible up until the first frost. If you missed this year set your calendars for next year! Our injector lending window is mid-July to early October. 

Many rhizomatous species are good to control in the fall with herbicide.

Rhizomes are a type of sideways spreading root system that can store energy and send up their own stems as new growth. Many plants spread this way.

This time of year, plants are pulling energy down to their roots, conserving energy for the winter months. Plants that have rhizomes and may benefit from fall treatments includes yellow loosestrife, knotweed, purple loosestrife, Himalayan blackberry, English ivy, and creeping thistle (just to name a few). Each species has their own optimal herbicide mix and timing, find your species specifics for most weeds here: Pacific Northwest Weed Management Handbooks. When using herbicides, always read and follow the label as there are restrictions for many herbicides in wet and other critical areas.

Click on a photo above and then click on the info icon to learn more about the rhizomatous species!

Cultural Control

But of course, you don’t want to just remove plants, you want to replace them with something. Otherwise, weeds will take advantage of the space and regrow from old roots or last year’s seed bank.

Cultural controls are any methods that change the local environment of the weedy species so that they are less likely to thrive, and desirable plants are set up for success. 

Besides being lovely to look at native plants have many ecological benefits such as cleaning air and water, erosion control, and habitat, as well as providing us mental and physical health benefits.  Cultural controls like planting native species, mulching, and pasture management are key for the long-term removal of noxious weeds. 

Mulching can be an excellent weed suppressant if done well. Read on for some tips and tricks to make mulching as effective as possible. 

A visual of mulching layers. The top later is 4-12 inches of heavy mulch, which is defined as arborist chips or bark/coarse mulch. The second layer is a paper layer, comprised of cardboard or newspaper. The final layer is weeded soil. 1-2 inches of compost layer are also interspersed throughout.
Sheet mulch is an effective strategy for weed control and overall soil health
  • More is more! The most common mulching mistake people make is not putting down enough of it. 4-6 inches minimum is a good rule of thumb for weed suppression. 
  • Level up your mulching game with dampened layers of cardboard or old newspaper! By adding a papery/compostable layer between your weeded area and mulch, you further suppress new weeds from coming back.
  • Feeding mulch feeds weeds too! To combat that, cover your feeding mulch (e.g. compost) with coarse organic mulch, like wood chips. To read more on the benefits of mulch read Mulch Matters.
  • Amend your soils! While weeds are known for thriving anywhere, they often have their own preferred conditions. Find out what they prefer and shift your soils to the opposite (consider existing beneficial vegetation in this plan, don’t compromise their health if you can avoid it). For example, preferences could be acidic or alkaline, or well drained or compacted.  
    • A soil test is a great way to start to determine exactly what your garden needs. Luckily King Conservation District (KCD) has you covered: Free Soil Testing.
  • Take your time! Weeds are much easier to pull from well-conditioned soil beneath good mulch. Most plants are done seeding by fall and won’t flower again until spring, so you have time. Mulch and amend your soils, let it sit for a few weeks to months, come back to easier to pull weeds! 

Ongoing pasture management is critical in keeping a healthy landscape and reducing weeds. This is the time of year KCD recommends applying compost and lime. They also recommend that animals are removed from the pasture when all grass is grazed grown to 3 inches, when the soils become wet, or by the first of November to allow plants to produce leaf growth for winter. When the desired pasture plants are not allowed to store energy for the winter months, they are more susceptible to being replaced by noxious weeds. Read KCD’s pasture management overview for more information.


Missing any of the tools needed for the task? Before going to your local hardware store, check out your local tool library! King Conservation District also has some specific tools they can lend out.  

Peruse our factsheets for the weeds below for more information on the species mentioned in this post. For other weeds, check out our website: kingcounty.gov/weeds.  

Fall is here! Time to enjoy the wonderful grey western Washington is known for by supporting all the hard work done over the summer to remove noxious weeds. If you have any questions or could use some support in making a strategy for your situation, send us an email at noxious.weeds@kingcounty.gov. #HappyWeeding!

One comment

  1. Thank you for your posts like this.
    Glad to see the instructions on using herbicides on some invasives which are basically uncontrollable without them. Have you experienced the sprouting of Herb Robert on top of wood chips? Does a layer of chips result in less moisture getting into the soil underneath? Last question , it seems like at least some of the native forbs prefer the poorer soils? I prepared a bed of good soil for some thimbleberry and it has struggled for 5 years while some nearby volunteer thimbleberry has spread rampantly nearby in a place with poor soil where I had merely cleared invasives.

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