How to Eradicate Japanese Knotweed


Japanese knotweed, sometimes called Japanese bamboo, is a fast-spreading perennial that threatens the native plant life of any area that it invades. This weed grows between 3 and 10 feet tall and spreads through underground rhizomes, which are root-like structures, and by seeds. The rhizomes of Japanese knotweed are very difficult to remove if left unchecked, as they have been known to reach up to 30 feet in length. It is important to eradicate Japanese knotweed quickly from your property because it can overtake large areas in a very short time.

Step 1

Put on a sturdy pair of rubber gloves before beginning. It's also wise to wear pants and a long-sleeved shirt to protect your skin from coming into contact with the chemicals used to remove Japanese knotweed.

Step 2

Mix the chosen herbicide according to instructions. Add liquid dye to the mixture and shake well. Make sure that you add enough dye to darken the solution substantially so that you will be able to tell which areas have been treated. Label the bottle to avoid confusion as to its contents.

Step 3

Clip the stem of the Japanese knotweed 2 to 3 inches from the soil using lopping shears. Spray the herbicide on the cut part of the stems as soon as you are finished clipping them. It is very important to do this promptly, as the plant develops a protective seal after being damaged that will prevent the herbicide from being absorbed.

Step 4

Do not mow or cut the stems for seven days after treatment. This will allow the herbicide to effectively penetrate the roots.

Step 5

Cut and treat the Japanese knotweed again in early fall.

Tips and Warnings

  • Use caution when mixing the herbicide because it will likely kill any grass or plants that it comes into contact with. Cut and spray Japanese knotweed on a day when no rain is expected for a minimum of one hour after treatment.

Things You'll Need

  • Rubber gloves
  • Spray bottle
  • Chemical herbicide
  • Liquid dye
  • Label
  • Lopping shears


  • United States Department of Agriculture: Invasive Species--Japanese Knotweed
  • University of Rhode Island: Japanese Knotweed Control Fact Sheet
  • Ohio Department of Natural Resources: Japanese Knotweed
  • Wisconsin Department of Natural Resources: Homeowner's Guide to Japanese Knotweed Control
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About this Author

Annita Lawson has been working as a freelance writer since 2004. Her work has been published in various web and print outlets, including The Dabbling Mum, A Virtuous Woman, and Pediatrics for Parents. Lawson is pursuing an Associate of Arts degree at Southeast Kentucky Community College. She enjoys sharing all that she has learned about parenting, healthy eating and living a frugal lifestyle.