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Japanese Knotweed #746535

Asked April 27, 2021, 11:37 AM EDT

Hello, I purchased a home in Crystal last fall, and this spring I am seeing Japanese Knotweed growing in a few of my garden beds, as well as creeping into my yard from a large patch in my neighbors yard. I have read the U of M Extension page about the plant, and know it is extremely difficult to eradicate, as well as very important to manage properly. I would like some guidance as to how I can remove this plant from my property so it does not continue to spread. The first photo is of the patch in my neighbors yard. The entire area between the fence and the buildings is full of Japanese Knotweed sprouts, all about an inch thick already. I just planted the Day Lilies on my property, and that is where it is spreading from my neighbors patch. The second photo is of a garden bed in the front of my house. The third is of sprouts in the garden bed in the back of my house. We removed some larger sprouts (half an inch thick by 20 inches tall) from the back garden bed before we knew what the plant was.

Hennepin County Minnesota

Expert Response

Unfortunately, if you're neighbor isn't going to eradicate the knotweeds, you will keep having them pop up in your yard. If you have a sharp spade I would periodically go along the edge of your fence to break any runners that the parent plant has sent under the fence.  

In your yard, I would recommend hand removal combined with an herbicide that includes glyphosate (the active ingredient in RoundUp). There are good instructions here: https://blog-yard-garden-news.extension.umn.edu/2018/06/aggressive-weed-challenges-mn-gardeners.html

If you are comfortable with it I would talk to your neighbor about removing the plants, knotweed is on the DNR's control noxious plant list and your neighbor is responsible for keeping it from spreading onto your property. You can share this page from the DNR on knotweed with them: https://www.mda.state.mn.us/plants/pestmanagement/weedcontrol/noxiouslist/knotweed

An Ask Extension Expert Replied May 02, 2021, 10:01 AM EDT

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