Fallopia japonica var. japonica (Japanese Knotweed)

Plant Info
Also known as: Mexican Bamboo, Hancock's Curse
Genus:Fallopia
Family:Polygonaceae (Buckwheat)
Life cycle:perennial
Origin:Japan
Status:
  • Invasive - ERADICATE!
Habitat:part shade, sun; moist, disturbed soil, fields, along roads and railroads, gardens
Bloom season:August - September
Plant height:6 to 9 feet
Wetland Indicator Status:none
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: 5-petals Cluster type: panicle

[photo of flowers] Flowers are in branching spike-like clusters in the upper leaf axils. Individual flowers are 1/8 inch across, white to greenish or pinkish, with 5 petals and 8 stamens. Male and female flowers are separate (dioecious).

Leaves: Leaf attachment: alternate Leaf type: simple

[photo of leaves] Leaves are simple, toothless, hairless, alternate, broadly oval to egg-shaped with a pointed tip, 3 to 6 inches long, 2 to 4½ inches wide, on a long stalk.

[photo of stems] A semi-woody perennial, it is fast growing and has hollow, bamboo-like stems that form dense, leafy thickets becoming woody with age.

[photo of shoots] Shoots arise from coarse, spreading rhizomes that can attain lengths up to 50 feet. 

Fruit: Fruit type: seed with plume

Female flowers can produce small 3-angled black-brown fruit but seed production is rare, primarily spreading by rhizomes.

Notes:

Japanese Knotweed goes by both latin names Polygonum cuspidatum (more common in North America) and Fallopia japonica (more common in Europe), with the latter accepted by “Flora of North America” (FNA, our definitive reference). Native to Japan, Japanese Knotweed was introduced to the UK in 1825 by gardeners as an ornamental. In the late 1800's it was brought to North America and quickly escaped cultivation. It is widespread in the eastern US and is likely now present in all of the lower 48 states. It is scattered across Minnesota and is winter hardy. While a major ecological threat to Minnesota's riparian areas, it is still carelessly moved from place to place by gardeners and is even still available in the garden trade. It is possibly in a garden center near you. FNA notes 4 varieties of F. japonica but there are also cultivars in the garden trade. The species described on this page is var. japonica. Dwarf Japanese Knotweed, var. compacta, is smaller with pink flowers and is less common but has also been widely planted in Minnesota. A hybrid between Japanese and Giant Knotweeds—Bohemian Knotweed (Fallopia × bohemica)—is also present in the state.

If you have Japanese Knotweed on your property: We discourage the movement and use of this plant for landscape purposes as it can quickly get out-of-control. We recommend control and removal wherever this plant is found. Control of this plant is extremely difficult once it becomes established. Digging of even small clumps is labor intensive and safe disposal of the rhizomes is problematic. Intensive mowing of tops or mowing in combination with herbicide applications (such as Arsenal®) can deplete this plant's energy reserves over time. There are no biological controls for Japanese Knotweed at this time.

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More photos

Photos courtesy Peter M. Dziuk, taken at locations across Minnesota

Comments

Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Alissa - Coon Rapids, MN
on: 2011-05-13 13:32:07

This plant is taking over the yard on one side of my house! It's sprouting up through the grass, in the window wells, everywhere! My last two seasons of work to get rid of them has seemed to do nothing! Any suggestions? Thank you!

Posted by: Diana - NE Mpls
on: 2011-09-21 19:49:02

My yard - actually my neighbor's, but encroaching into mine. I understand ridding us both of this will be my new hobby.

Posted by: Cynthia - golden valley
on: 2012-04-20 13:29:34

i would like to grow this in pots (to keep it from spreading) due to its effectiveness in treating Lyme disease ("Healing Lyme" Stephen Harrod Buhner, 2005). Purchasing the herb is very expensive, and treatment often lasts longer than a year.

Posted by: K. Chayka
on: 2012-04-21 21:01:49

Cynthia, if you must have these plants, keep them in pots and keep them indoors.

Posted by: Annette - Falcon Heights MN
on: 2012-04-28 19:26:33

I have shoots. When I bought my house there was a huge forest of the stuff. Over the past two years I have cut it all down and and am still mowing some smaller shoots and applying roundup.

Posted by: Deb - Eden prairie
on: 2012-08-08 19:36:17

I have a spreading area of this. Thought it was a pretty plant and smelled good. Now I know what it is and have been trying to eradicate it. Last year I cut some at ground level and IMMEDIATELY doused with undiluted Super Concentrate Roundup using a sponge paint brush. I also sprayed the diluted mixture on new plants (less than 12" tall). The cut and douse method seemed to work well. That area has minimal regrowth. The sprayed plants have deformed, very small leaves, but they continue to grow, albeit slowly. Plans are to do more cut and douse. I was told to douse immediately after cutting as the plant seals itself quickly after bing cut. It's a slow process, but seems to work. It will probably be a yearly battle as with buckthorn for several years (have that to contend with also in the same manner.)

Posted by: joe - Taylors Falls
on: 2012-10-04 13:35:00

Actually I'm in Amery, Wi. just a few miles east of Taylors Falls. I'm interested in digging some roots. This is kind of urgent, as I have a friend with reacurring Lymes, and needs this soon. Thank You Joe

Posted by: K. Chayka
on: 2012-10-24 08:14:28

To anyone requesting or wanting to share information about Japanese knotweed and Lyme disease: Minnesota Wildflowers is not a forum for this issue. There are many other web sites devoted to Lyme disease and/or natural healing that would serve you better. Please use those resources instead. Thank you.
Katy Chayka, Minnesota Wildflowers

Posted by: Linda - Greenfield
on: 2012-11-28 00:55:56

I'm really sorry to see that you do not welcome inquiries regarding Japanese knotweed if we are interested in using it for natural medicinal purposes. I'm puzzled actually. I am interested in getting anyone's plant to grow in a pot inside year round. Please contact me if you are willing to help me. Thanks so much.

Posted by: K. Chayka
on: 2012-11-28 06:44:20

Linda, et al: Minnesota Wildflowers is just a field guide--we are all about plant identification and promoting natives in the landscape. Putting people in touch with each other regarding the procurement of invasive species, regardless of the reason, goes against the mission of Minnesota Wildflowers.

We are not experts on natural medicine or food value of wild plants, nor do we wish to become a clearinghouse for such things. There are numerous other venues with more information and authority than we can provide.

So I am sorry, but we cannot help you. Good luck in your quest.

Katy Chayka, Minnesota Wildflowers

Posted by: Ghislaine - Minneapolis
on: 2013-04-25 11:56:23

Came across some interesting recipes for the young shoots of this - anyone know of a publicly accessible clump in the metro area where I could dig some up?

Posted by: Connie - Minneapolis
on: 2014-05-31 19:21:13

A woman, who claimed to be a Master Gardener, was holding a plant sale in White Bear Lake. She sold me a plant she said was Bamboo. It turned out to be Japanese Knotweed. At first I thought it was so beautiful. But after it started spreading everywhere, I panicked. I ended up getting info from the horticulture dept. at UMN. I was told to spray the leaves with Round Up. I covered the plant, where I was able, with plastic bags and sprayed and sprayed. As it died, I went after the roots. I dug deep and far to get them out of there. I was afraid it was going to grow in the cracks of the sidewalks. Thankfully, I have gotten rid of it.

Posted by: Erica - Roseville
on: 2014-07-23 13:35:44

Japanese knotweed is growing in mass in several places along Victoria just south of County Road B in Roseville. (Ramsey county and Roseville have been alerted, but private landowners in the area may want to know)

Posted by: Andy - On Co Rd 27 SW near Crooked Lake in Falwell
on: 2014-09-17 10:01:41

Large flowering stand seen flanking the driveway of a private residence, near the public landing for Lobster Lake.

Posted by: Nicole - Hastings
on: 2015-05-12 09:49:56

We've read that in the UK, that Japanese Knotweed plants were actually coming through the foundations of houses and growing. Is there worry of this happening with the growth of these plants here in Minnesota?

Posted by: K. Chayka
on: 2015-05-12 20:04:33

Yes, Nicole, Japanese knotweed can crack foundations here as well.

Posted by: Carole - Shoreview
on: 2015-09-21 10:57:53

I was contacted by a Shoreview city volunteer group, replanting a boulevard, wanting id and removal advice. Their plant was the dwarf pink. I asked for but have not received an exact location yet. BTW; EDDMapS now lists this plant as Reynoutria japonica Sieb. & Zucc.

Posted by: K. Chayka
on: 2015-09-23 17:19:34

Flora of North America still lists it as Fallopia japonica, with Reynoutria japonica Houttuyn a synonym.

Posted by: Teri - Robbinsdale
on: 2016-08-12 11:46:13

There is a large bank of Japanese Knotweed along the channel coming out of Twin Lake, where there is a footbridge crossing near 46th Ave, 2 blocks west of France Ave.

Posted by: Lynn - Lake Elmo
on: 2017-01-27 14:35:31

My neighbor brought it back from Wisconsin and planted between our yards in terraces. I've been trying to remove. It's very difficult.

Posted by: Tom W - Mendota Heights
on: 2017-06-28 15:52:58

My fathers backyard has been overtaken by this stuff.

Posted by: Erica T - Roseville
on: 2017-07-20 13:37:55

Roseville has been battling this for a few years now, and I've heard Stillwater as well. A huge hedge was treated along Victoria near Reservoir woods. It required multiple treatments to remove many plants near the wetlands but the plant came back in full force on private properties in the area that were only treated once. I now see small plants popping up on residential properties between Victoria and Dale (south of County Road B). Just a note to the herbalists.... When it is farmed for food or root derivatives in its native country, they use bulldozers to get the roots which can span up to 60 or so feet. Even though it might be used for nutraceutical production, it easily escapes cultivation (so recommend letting those from country of origin do the farming).

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