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Japanese Knotweed Flowering

9-12-18 Japanese bamboo_U1A9517Japanese Knotweed (Fallopia japonica) was introduced from Japan in the 1800’s as an ornamental; it was widely cultivated, escaped and is now well established throughout the Northeast. The World Conservation Union lists Japanese Knotweed among the top 100 worst invasive plants.  Its dense canopy and rapid spread through underground rhizomes make it a formidable threat to native plants and the animals that depend on them.

There are some redeeming qualities to this invasive plant, however. In addition to goldenrod and asters, Japanese Knotweed is a crucial source of late-season nectar and pollen. At this time of year, when Japanese Knotweed flowers, you can almost locate a stand using just your ears, the buzzing of honey bees gathering the last of their winter food supply from the thousands of tiny flowers is so loud.  A wide variety of  insects can be found on this member of the Buckwheat family eating leaves, foraging for nectar and pollen, and preying on the former. A recent survey revealed honey bees, bumble bees, ladybug beetles, flies, hornets, yellow jackets, stink bugs and tussock caterpillars, to name just a few.

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21 responses

  1. Barry Avery MG

    You can plant any number of Persicaria, closely related to the evil Knotweed, that provide the same benefits, are more colorful and are not invasive.

    September 12, 2018 at 8:44 am

  2. Carolyn Boardman

    What about a benefit for monarch?

    September 12, 2018 at 9:02 am

    • I’ve actually never seen a monarch on it, but that’s entirely possible!

      September 12, 2018 at 1:24 pm

  3. Thank you for highlighting the benefits of Japanese knotweed. It is also being used as a medicinal ~ the roots contain resveratrol which is useful in treating Lyme disease. In Japan, it is known as Itadori which means “healing the sick”.

    September 12, 2018 at 9:32 am

  4. Allison Bell

    Please don’t promote this plant’s “redeeming” qualities. Late season pollen/nectar is better supplied by the native plants it displaces.

    September 12, 2018 at 9:40 am

  5. Alice Pratt

    Another name for this plant, is ‘Donkey Rhubarb’, which I think is hilarious…it’s really difficult to eradicate…I’ve heard that if it is mowed, and you bring home a piece on your footware, it will start a new plant…it grows ‘all over the place’ around here…and spreads & spreads

    September 12, 2018 at 9:46 am

  6. My biggest question is if there are any other plants which can be planted to stop the spread? I know about mowing and mowing, but I wonder if there is an equally formidable plant which the knotweed won’t move past? I include trees in this query. Black walnut with its toxic roots? Or even another invasive like purple loosestrife? Someone getting their degree in Ag could run experiments to see, dubbing it The Battle of the Giants!

    September 12, 2018 at 10:16 am

  7. Tami

    Took us five years of pulling it up by hand as soon as the shoots started showing, but we think we may have finally done in the small patch at the state park I work at. Maybe. If we’re lucky.

    September 12, 2018 at 10:29 am

  8. viola

    How nice to know there are some redeeming qualities as I pass Japanese knotweed EVERYWHERE on my outs and abouts. I hadn’t realized it had been in this country for such a long time. I understand it was prescribed for holding the soil and preventing erosion when installing culverts in road building for many years.

    September 12, 2018 at 10:42 am

  9. Amy Harris

    Not only is knotweed beneficial to insects, it is an early spring vegetable for humans! when it comes out of the ground in the spring and is still a small stalk, it can be cooked and eaten a little like asparagus, or substituted for rhubarb in a pie!

    September 12, 2018 at 11:36 am

    • Alice Pratt

      …..an invasive wild-edible 😬

      September 12, 2018 at 11:43 am

  10. Bill on the hill

    Unfortunately, according to my forester, pulling up, burning out, mowing it down, etc. will not stop its spread and may actually make things worse. The only effective treatment that I am aware of based on advice from my forester is through the use of herbicides, which kill it all the way down to the root systems in the plant. I have had small patches on my property for the last 20 years & they indeed have spread on their own with NO help from me. Personally, I am hesitant on the use of chemicals on my property with respect to water quality outflows into my spillways, as well as small & large animals, insects, etc. that traverse the land… So in the meantime, I continue to be annoyed by this invasive plant!

    September 12, 2018 at 12:38 pm

  11. redpathw@tiac.net

    The plot thickens. Thanks. Maybe there is a recipe for knotweed soup???

    September 12, 2018 at 1:07 pm

  12. My naturopath/Lyme specialist has a multi-pronged approach to treating tick bites and Lyme disease, It includes prescribing an herbal blend comprised of knotweed root extract (and other herbs as well) as a powerful anti-Lyme disease remedy!

    September 12, 2018 at 1:50 pm

  13. Whoops, I meant Lyme disease remedy, not “anti-Lyme disease remedy”! 🙂

    September 12, 2018 at 1:55 pm

  14. The horse is out of the barn, folks… this one is here to stay. Impossible to eradicate, I fear.

    September 12, 2018 at 5:29 pm

  15. Jennifer Waite

    I’m surprised that it was ever recommended for erosion control – it hastens riverbank erosion to a terrible degree! and contributed quite a bit to the flooding problems after Irene. Even if a bee enjoys it, I’m afraid I can’t find any trace of affection in my heart for nasty knotweed, haha!

    September 12, 2018 at 5:48 pm

  16. Tom P.

    Glyphosate works really well on this plant. And it comes in formulations that are safer for water ways.

    September 12, 2018 at 9:27 pm

  17. Sylvie Desautels

    I have an herbalist friend who touts many medicinal properties for Jap Knotweed.

    September 12, 2018 at 9:56 pm

  18. Peggy Timmerman

    There is nothing redeeming about invasive species that we have moved around the planet, intentionally or not, and that impoverish the local diversity of the flora. If they have medicinal qualities they can be grown in controlled environments like greenhouses, with appropriate education of all who work with them, so they do not become a problem in our natural and agricultural areas. While knotweed may provide a late season nectar source, as a non-native plant it cannot be utilized by most insects during any other part of their life cycle. See Douglass Tallamy’s wonderful book “Bringing Nature Home” to learn more about this important issue.

    September 17, 2018 at 11:04 am

  19. We really like your site, it has engaging articles, Thank you!

    December 3, 2018 at 2:26 am

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