How to kill Japanese knotweed


How to kill Japanese knotweed


Knotweed (often referred to as Japanese Knotweed) is a a shrub-like perennial weed that’s native to Eastern Asia and has spread to the Western world. In fact, it grows so quickly that knotweed is difficult to contain and spreads easily from one site to another. As it spreads, Japanese knotweed alters and threatens ecosystems. For that reason, the Plant Conservation Alliance, a United States government-run group, advocates killing the plant. Once you’ve killed the weed it’s important to dispose of it properly. The best way to do so is to place it in a garbage bag and throw it in a can or dumpster to prevent future reestablishment.

Step One

Cut the knotweed stems just below the bottom joint with gardening shears at any time during the growing season. Put the tops of the plants in a pile where they can dry out and die.

Step Two

Fill a small glass with liquid Glyphosate herbicide. Do not dilute the herbicide with water. Doing so will only make it weaker.

Step Three

Pour a tablespoon of the herbicide into the hollow stem of each knotweed plant. Be cautious about dripping it on any surrounding plants or grass as it will likely kill them.

Step Four

Make a mixture of diluted herbicide in a garden sprayer. All herbicides are different, so follow the directions on the package carefully.

Step Five

Spray the plants with the herbicide once every three weeks until the ground freezes over. If the ground does not get cold enough, continue spraying the herbicide every three weeks until the plant dries out completely and dies.

Step Six

Repeat the same process the following year. Knotweed has roots that can grow up to 10 feet deep, so it can take up to three years of work to completely kill it off. Once completely dead, it's best to remove the entire knotweed system, including the roots. This prevents any future growth.


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