ArborActive Tree Care Guide
How to Control Japanese Knotweed in CT, MA & RI
By ArborActive Team · Updated
Knotweed can start new plants from fragments. Plan how to contain stems and soil before cutting or digging, especially along a stream.
Identify the plant
Reynoutria japonica. Look for upright, jointed canes with hollow stems, broad leaves with a fairly flat base, and sprays of pale flowers later in the growing season. Giant and hybrid knotweeds can look similar.
University of Connecticut Extension identification and management guideChoose a control method
Start with the size of the patch, what you want to preserve and whether the site is near water.
Small patches
Mark the edges of the patch and keep it out of routine mowing. Cutting alone generally suppresses top growth. Where repeated cutting is chosen, contain all fragments and plan to continue over successive seasons.
Established infestations
A professional may consider a labeled systemic treatment once the plant has enough healthy foliage to move it toward its underground rhizomes. Excavation can spread the infestation if rhizomes or contaminated soil are moved. Discuss site restrictions and disposal before disturbing a bank or wet area.
Keep it from coming back
Inspect beyond the original patch and check where runoff or equipment could have carried material. Avoid putting canes or rhizomes in a home compost pile. Ask the local waste authority which disposal options accept knotweed.
Check local requirements
Before moving plant material, working near water or using an herbicide, check the rules for your property. Use only products labeled for the plant and site, and follow the label. Ask the local authority about disposal.
Connecticut invasive plant list
Check the current regional guidance before work.
Connecticut invasive plant listMassachusetts prohibited plant list
Check the current regional guidance before work.
Massachusetts prohibited plant listRhode Island invasive species resources
Check the current regional guidance before work.
Rhode Island invasive species resources
Common questions
Will digging out the visible shoots solve it?
Shoots are only the visible part. Rhizomes extend below ground and can resprout from fragments. Decide how to contain and handle the material before excavation.
Ask ArborActive about your property
Send your town, the approximate patch size and a photo of the suspected japanese knotweed. Mention nearby water and plants you want to keep.