How to Manage Japanese Knotweed

Overview

Japanese knotweed (Polygonum cuspidatum) originated in eastern Asia, and was introduced to the United States as an ornamental plant for erosion control. It has now spread through many states through seed transfer and rhizomes. This tough weed is a perennial shrub, growing 4 to 10 feet in height. It blooms from August to November, with brown fruits following until January. Knowledge of how to manage this plant will help you remove it completely.

Step 1

Identify Japanese knotweed early, as if the infestation is small, you have a better chance of getting rid of it. It sprouts and grows quickly in the spring with stems that resemble bamboo. In late summer, tiny white flowers arranged in sprays appear followed by brown, triangular, shiny seeds.

Step 2

Dig or till the area in early spring, removing all parts of the Japanese knotweed. Any part left in the soil can potentially re-sprout. Bag and trash all collected parts to stop any potential spread.

Step 3

Cut the remaining branches down to the ground throughout the spring and summer. By late summer, the Japanese knotweed should be 3 to 4 feet tall, instead of the 10 feet it will grow to without cutting.

Step 4

Apply an herbicide with glyphosate on the cut stems. Follow the directions on the package for application and safety instructions, as each herbicide will differ. If the Japanese knotweed come back again in the same season, apply the glyphosate herbicide to the leaves, again, following the directions.

Step 5

Repeat this process the following year. It will usually take two to three years to eradicate the Japanese knotweed.

Things You'll Need

  • Spade
  • Rototiller
  • Pruning shears
  • Glyphosate herbicide

References

  • Plant Conservation Alliance's Alien Plant Working Group: Japanese Knotweed
  • Nature Conservancy: Controlling Knotweed
  • North Carolina State University: Japanese Knotweed
Keywords: Japanese knotweed control, killing Japanese knotweed, managing Japanese knotweed

About this Author

Sarah Morse recently graduated with a Bachelor of Arts in English language and literature. She has been freelancing for three months and got her start writing for an environmental website.