Ask Extension: What to do about knotweed?

UNIVERSITY OF MINNESOTA EXTENSION - www.extension.umn.edu

We recently purchased a new house and discovered we have a plant called knotweed taking over the backyard. We have tried digging it out, but are still unable to get rid of it. What should we do? We understand that it is an invasive plant in Minnesota.

Bohemian knotweed

Good for you for recognizing this invasive species and noxious weed! And thanks for contacting us about its management. Knotweed is very deep-rooted and difficult to eradicate, but it is important that you remove it.

Japanese knotweed, Bohemian knotweed and Giant knotweed are listed on the Minnesota Department of Agriculture's (MDA) Noxious Weed list.

Knotweed was once a prized ornamental in the 1800s but soon recognized as an invasive plant in the 1900s. One of the challenges to controlling knotweed is that it spreads by both rhizomatous roots to form dense colonies, and it spreads by seed that is carried by wind. It outcompetes desirable plants by creating dense shade, absorbing water and nutrients in soil, and taking over space.

You'll need to start by identifying the species of knotweed (Japanese, Bohemian or Giant). This is important because eradication methods vary depending on the species. Identification features are available on the links above.

Report knotweed

You should report your knotweed to the MDA using the Great Lakes Early Detection System (GLEDN) app or go to the MDA's Arrest The Pest webpage. It is important for the MDA to know about infestations so as to assess and understand the extent of an invasive species in our state.

Citizens reporting what they have or find is crucial to forming strategies for management and reducing populations of invasive species. You will not be penalized in any way for reporting.

Find out more

Bohemian knotweed, a major noxious weed by Mary Meyer, University of Minnesota professor emeritus in horticulture