How to Deal With Japanese Knotweed
This invasive plant can be hard to tackle, but with these tips and some patience you can get it under control.
Japanese knotweed is a semi-woody perennial that can grow in a variety of conditions, including compacted, impoverished soil—or worse, cracks in your driveway, sidewalks, or the foundation of your home. In other words, it's a highly invasive plant able to grow where many others cannot. This also means, unfortunately, that it's difficult to get rid of once it's taken root.
There are other types of knotweed found across the U.S., but Japanese knotweed (Fallopia japonica) is the one that makes headlines for its particularly tenacious behavior. It grows above ground in thick, upright patches up to 11 feet tall, and below the ground as rhizomes, too; underground root networks as large as half a football field have been reported. If you're getting the sense that stopping it in its tracks is essential, you're right. Don't put off containing or removing it if you see Japanese knotweed near your home.
What Does Japanese Knotweed Look Like?
- Flower clusters that sprout from the nodes (the point where a leaf attaches to the stem)
- Hollow, light green to reddish-brown stems that resemble bamboo
- Alternate, broad, spade-shaped leaves
- Clusters of small, greenish-white flowers
How to Kill and Prevent Knotweed
Getting rid of knotweed requires a two-pronged approach (cutting and a control product) and more than one season. Remember, each fragment of root left in the ground can be the basis of a new knotweed plant, so cut it back carefully.
- While you can't fully prevent Japanese knotweed from moving in, a healthy lawn and well-maintained hardscapes can reduce the chances. Keeping the plants you do want in your yard nice and strong helps to crowd out potential invaders.
- Always buy topsoil or any vegetation you plan to plant from a reputable source to reduce the chance of introducing knotweed into your yard.
- If you spot Japanese knotweed on your property, start cutting the stems down to the ground with a sharp pair of clippers every 2 to 3 weeks (or more), from spring through summer, to help exhaust its root system. Stop 8 weeks before applying any control product.
- If Japanese knotweed has sprouted up in your landscapes or hardscapes, use Ortho® GroundClear® Super Weed & Grass Killer. The spray formula works deeply, reaching the roots to help kill it at the source. For yards, apply Ortho® Weed B Gon® plus Crabgrass Control Concentrate, which will begin eliminating knotweed while keeping your grass safe. Always follow all label directions, and know that even with the help of a control product, it will take at least 2 seasons to get rid of Japanese knotweed and continual monitoring after that.
- Never compost knotweed, as it can contaminate what's there and continue to sprout and spread. Place it up in a heavy-duty plastic bag before disposing of it in your trash so there's no chance for it to spread at a landfill, either. For larger problems, you can let it dry out on a tarp and contact your local waste management service to ask if they take invasive plants, or, if not, the best way to dispose of it. You can also call your local extension service.
Japanese knotweed is not fun, plain, and simple. Discovering it around your yard can seem daunting, and with good reason—it is one of the hardest invasive weeds to tackle. But with these tips (and a lot of patience) you can ultimately overcome it and get back to growing what you love.