How to control Japanese knotweed

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Japanese knotweed
Japanese knotweed. By Ancatdubh43 at English Wikipedia [Public domain], via Wikimedia Commons

Ever heard of Japanese knotweed?

The Ohio Department of Natural Resources lists it as one of the state’s top invasive species, among the ranks of Japanese honeysuckle, garlic mustard and purple loosestrife. The shrub-like herb can grow up to 10 feet tall, its underground root system can grow up to 60 feet in length and it’s not exactly easy to control.

Japanese knotweed originated in parts of Asia — Japan, China, Korea and Taiwan — and was introduced in the United Kingdom in the early 19th century as an ornamental plant, according to the Indiana Plant Species Assessment Working Group (IPSAWG).

What does Japanese knotweed look like?

Japanese knotweed has reddish-brown hollow, smooth stems and swollen nodes, the Ohio Invasive Plants Council explains. The plant’s leaves are pointy and can be oval-shaped or triangular, and they are about 4 to 6 inches long and 2 to 3 inches wide. Japanese knotweed flowers in late summer. The plant’s flowers are small and green-white in color.

Where does Japanese knotweed grow?

Japanese knotweed grows in open areas, according to ODNR. You can find it along roadsides, riverbanks and woodlands. The plant grows in moist environments.

Japanese knotweed typically emerges and begins to grow in early spring. It’s underground rhizomes grow quickly, allowing the plant to expand into dense thickets, according to The Wisconsin Department of Natural Resources.

Does Japanese knotweed grow in Ohio?

Japanese knotweed is pretty common in the Buckeye state, especially in eastern Ohio.

The Ohio Invasive Plants Council offers a map that shows the counties in which Japanese knotweed was reported, as of 2010.

Can you eat Japanese knotweed?

Surprisingly, you can.

In Pittsburgh, knotweed grows in abundance in empty lots and along the city’s rivers. The Wall Street Journal takes a look at how the invasive weed is being used in culinary creations at local restaurants and urban farms. So far, knotweed has been used in sauteed dishes, honey, beer, ice pops and even desserts.

How do I control Japanese knotweed?

If Japanese knotweed has made a home on your property, you can control it mechanically or chemically.

The Wisconsin Department of Natural Resources explains that cutting off the aboveground portion of the plant doesn’t really solve any problems, as it will continue to grow from its underground roots. The plant’s energy comes from its rhizome. However, weekly mowing of the plant can wear down on its energy reserves, helping to eradicate the plant.

If Japanese knotweed has become widespread and thick, digging up each plant will be time and energy-intensive. The Ohio Invasive Plants Council says that if there are only a few plants, consider digging them up, making sure to remove underground rhizomes. Dispose of the plant in plastic bags. Physical removal of the plant may have to be repeated in a single season.

As for chemical control, the Ohio Invasive Plants Council says that spot application of products like Roundup or Habitat, along with repeated cuttings, can help to get rid of Japanese knotweed. Read more about chemical applications here.

ODNR recommends spraying leaves, cutting the stems and spraying the plant with herbicide. A full how-to that combines mechanical and chemical control can be read on this Wisconsin Department of Natural Resources guide.

Have any other tips for Japanese knotweed control and removal? Let us know in the comments section.

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Katie Woods grew up in Columbiana, Ohio. Katie likes reading, writing, enjoying the outdoors and DIY projects.

6 COMMENTS

  1. Japanese knotweed is listed as a noxious weed in Ohio for a very good reason. If you spray it for 10 years like I have it does not die. It travels down stream and down the road on mowers. It destroys stands of native plants. If you dig it up double bag it and send it to a landfill or an incinerator. I have seen it spread under asphalt and sprout up thru it. If an intact stem and node are in contact will the soil it can sprout from one small piece of the plant and regenerate itself. It can be spread by ditch cleaning and other excavation work.
    Never accept plant waste, mulch or fill etc unless you know knotweed is not in it!
    If you have it please control it. If you do not learn what it looks like and watch for it and catch it early.
    Finally, if you have an interest in preserving Ohio’s natural history on public lands please volunteer to help with invasive plant control, with ODNR, county parks, The Nature Conservancy, Western Reserve Land Conservancy, The Cleveland Museum of Natural History…….

    Thanks for the article Katie.

  2. Something not mentioned in the article is that Japanese Knotweed can sprout from a pea-sized piece of plant material or root. Mowing or cutting this plant and leaving the stems on the ground, or dumping the brush is causing the problem to be worse. In addition to the spread through fragments, cutting/mowing STIMULATES root growth. (If you’re not mowing constantly and picking up the pieces, you’re helping it spread) So I cringe when I see a lot of new articles talking about preparing it for food that DON’T mention that it shouldn’t be composted, and that by cutting it they’re increasing the underground growth. One city here in Michigan had someone put clippings in the compost, which then went to other residents, and now the whole town has it.

    I’m the Tall Grass and Weed Inspector for the City of Kalamazoo, MI and I’ve been working with the Kalamazoo Nature Center to mobilizing an awareness campaign to stop people from spreading it while we wait for effective treatment options. Roundup/glyphosate alone actually INCREASES the growth of this plant, so I don’t know why people/governments keep recommending it. Dr. Leslie Kuhn from MSU has seen some success in her work fighting it. The Stewardship Network has a 1 hour webcast about treatment available on their website.

    This plant is going to take over the world (Just look at what it’s done/doing in the UK. Our governments need to start paying attention because there’s a lot we could do to PREVENT new growth, and as they say, “A stitch in time saves nine”. (It also is transported often through construction equipment and soil being moved. Check out Cornwall England’s website. THE BEST stuff there!) https://www.cornwall.gov.uk/environment-and-planning/trees-hedges-and-woodland/invasive-plants/japanese-knotweed/

    • Doesn’t composting it kill any seeds? Correctly composting should result in heat in the compost that should kill any seeds that might spread the plant, shouldn’t it? When dropping of another invasive plant from my area, I asked at the city landfill if putting my
      yard waste would spread the plant. I was assured by an official that their multi-step of composting would kill any seeds or plant parts which could spread the weed.

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