How to Deal With Japanese Knotweed

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?

Japanese knotweed starts as red bamboo- or asparagus-like shoots that quickly grow into big, shrub-like weeds and a big headache. Using those rhizomes that spread underground, it can start new weeds far away from the parent plant. Any broken part of the plant, including stems, rhizomes, or crowns, can start a new weed, making its spread even easier and more prolific.

Here are the main characteristics of Japanese knotweed: 

• 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 or asparagus
• Alternate, broad, spade-shaped leaves
• Clusters of small, greenish-white flowers

While many other plants can be mistaken for Japanese knotweed, the quickest way to tell you have this weed is by the combination of hollow, bamboo-like stems and broad spade-shaped leaves. Giant knotweed and the hybrid Bohemian knotweed are relatives of Japanese knotweed that can be distinguished by their much bigger leaves.

Japanese knotweed can be found throughout most of the contiguous U.S., with the exception of some Southern states. This perennial plant thrives in a variety of conditions from full sun to shade and poor soil conditions, which only adds to its reputation as a menace. Given its preference, this weed grows in sunny spots near rivers and streams, where it can cause serious damage by crowding out native plant species and facilitating soil erosion. It's also pretty partial to sunny roadways, which means you see it as you're out driving on open highways.

How to Kill and Prevent Knotweed

Getting rid of knotweed requires a two-pronged approach with cutting and a control product, and also takes 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. Take action quickly if you spot Japanese knotweed, and stay vigilant to get ahead of an infestation.

Prevent Japanese Knotweed

While you can't fully prevent Japanese knotweed from moving in, you can take these steps to help keep it out of your lawn and landscape:

• A healthy lawn can help crowd out weeds. Our friends at Scotts recommend 4 annual feedings to keep your lawn doing its best, in addition to regular mowing and watering.
• Well-maintained hardscapes can reduce the chances of weed growth. Keep your hardscapes like patios, sidewalks, and driveways clean and fix cracks as you're able.
• Keep the plants you do want in your yard nice and strong to help crowd out potential invaders with regular feeding, watering, pruning, and other maintenance tasks. Need advice? Check out resources and products at Miracle-Gro.
• Always buy topsoil or any vegetation you plan to plant from a reputable source to reduce the chance of introducing knotweed into your yard.

Kill Japanese Knotweed

If you've already spotted Japanese knotweed on your property, get serious before it can become an infestation. Even under the best circumstances, eradicating Japanese knotweed takes at least 2 seasons, so prepare for a long fight when you're dealing with this weed. You're going to need that 2-step approach of cutting back weeds and using a control product we mentioned earlier:

• 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 cutting back 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. If Japanese knotweed is around homes, cabins, buildings, fences, or trails Ortho® Groundclear® Poison Ivy & Tough Brush Killer has you covered.
• For lawns, apply Ortho® Weed B Gon Chickweed, Clover & Oxalis Killer for Lawns Ready-To-Spray which will begin eliminating knotweed while keeping your grass safe. 
• When using weed control products, always follow all label directions. 

After removal, continually monitor your lawn and landscape for new shoots. Unfortunately, you may never be 100% free of this weed, but the earlier you can start removal, the better.

Dispose of Japanese Knotweed

After you've cut away Japanese knotweed, don't just let it spread somewhere else! Remember that any part of plant can sprout new weeds, so be careful when disposing of Japanese knotweed:

• 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. 
• 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.