Japanese Knotweed (Reynoutria japonica)

Common names:
Give a thumbs up Japanese Knotweed
Give a thumbs up Asian Knotweed

Botanical names:
Reynoutria japonica Accepted
Fallopia japonica Synonym
Fallopia japonica var. compacta Synonym
Polygonum cuspidatum Synonym

General Plant Information (Edit)
Plant Habit: Herb/Forb
Life cycle: Perennial
Sun Requirements: Full Sun to Partial Shade
Minimum cold hardiness: Zone 4a -34.4 °C (-30 °F) to -31.7 °C (-25 °F)
Maximum recommended zone: Zone 8b
Plant Height: 8-10 feet
Flowers: Showy
Flower Color: White
Bloom Size: Under 1"
Flower Time: Late summer or early fall
Underground structures: Rhizome
Wildlife Attractant: Bees

and this one is a baby one!

Posted by CLUSIANA on Aug 19, 2012 2:37 PM

This plant is the worst thing I have ever seen. You cannot get rid of it. If you leave a tiny piece of root in the ground, you get a new plant, and if you cut it back, it grows during the night and you find new growth in the morning. I have been carrying tons of ground to get rid of it. Even being against the use of chemicals in the garden, I think I am going to try to get rid of it that way, and I am wondering if that will work. Nice in bloom, but a real nightmare when happy somewhere. Loves water and here the water table is very high.

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Posted by bonitin (Ghent, Belgium - Zone 8a) on Jun 13, 2016 3:16 AM

This plant is attractive in many ways. The problem is that it chokes out all other vegetation by its aggressiveness. It is a real pest over here, where it is a serious threat to the native flora, especially along river banks. Avoid at all cost the temptation to plant it in your garden, from where it can escape.

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Posted by ILPARW (southeast Pennsylvania - Zone 6b) on Sep 22, 2019 8:18 PM

While this Reynoutria Fleeceflower or Japanese Knotweed has some beauty, it is a very invasive East Asian plant in North America and Europe, where it was introduced as an ornamental and even as a food source. I once was planning to plant some of the compact variety (that gets about 12 to 18 inches high) in some parking lot islands back in the 1990's on the grounds of a facility, but fortunately never did it. I have used a sickle on the tall, standard species and it cuts down very easily with its hollow stems. The only way to get rid of it is to constantly attack it with cutting and mowing every week, and using some herbicide as glycosphate when it is small and growing also will help. Big woody plants that will shade it will also weaken it. I recently found a few small patches of the compact variety in a landscape of a business park in Naperville, Illinois, that were fortunately planted in constrained small areas surrounded by concrete. So, the Polygonum cuspidatum compactum or Fallopia japonica compacta is still being offered by some conventional nurseries.

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Discussion Threads about this plant
Thread Title Last Reply Replies
any idea what this plant is? by mrnewbie Nov 20, 2019 7:21 AM 9
does clematis revert to a "wild" vine when transplanted? by cmaizel Jul 26, 2019 8:20 PM 14
Need help identifying by blackwidow716 Jul 7, 2019 4:14 PM 1
Bush ID by tinypiney Oct 1, 2018 9:51 PM 4
What is this? by RainbowChild Jun 8, 2018 5:49 AM 2
What is this plant? by Lucy7550 May 7, 2018 6:31 PM 8
What is this volunteer? by JuniperAnn Dec 4, 2017 6:41 PM 5
What is this plant's name by junglewanderer Oct 7, 2017 9:04 AM 7
Identify by ejdodier Jun 30, 2017 8:27 AM 2
What is this? by MikeR1991 Jun 22, 2017 5:59 AM 4

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