By Peter Mitchell
and Riley Buley
The invasive plant knotweed persists in Fillmore County. Native to Asia, knotweeds were first planted in North America in the late 1800s as ornamental garden plants. They escaped cultivation and have spread to most states. In their native range, knotweeds are early colonizers after volcanoes with stems pushing through volcanic rock. Similarly, stems can grow through pavement and building foundations necessitating costly removal and repairs. Japanese knotweed is a regulated weed in Alabama, California, Connecticut, Iowa, Idaho, Illinois, Massachusetts, Minnesota, Montana, Nebraska, New Hampshire, Ohio, Oregon, Vermont, Washington, West Virginia, Wisconsin and Wyoming.
Knotweeds are Herbaceous perennials (non-woody plants that return each year) with shrub-like forms that can exceed 10 feet tall. Multiple, hollow stems form a clump that resembles bamboo. Stems die back to the ground after hard frost and new stems emerge in the spring. New shoots sprout from spreading rhizomes (underground stems) that can grow to 65 feet long. Leaves are alternate, simple and broadly oval with pointed tips. Flowers are produced in white clusters in the late summer. Knotweeds are fast growing and can form dense infestations. Knotweeds can grow from pieces of stems and rhizomes so pieces must be managed carefully to prevent new infestations. Knotweed can also spread by seed. Chemical treatments, spring and summer mowing, grazing, smothering, and physical removal of knotweeds are all methods to remove this plant. It is important to consult product labels as well as talk to a professional before attempting treatment.
In 2024, Fillmore SWCD secured funding though the Minnesota Department of Agriculture’s Noxious Weed and Invasive Plant Grant to treat 0.85 miles of stream banks along Maple Creek against knotweed. This area was again treated by the Minnesota Department of Agriculture in 2025. Knotweed was also observed near Lanesboro and is likely observed throughout the county. More information and a pamphlet on knotweed removal can be had by contacting Fillmore SWCD.
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