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.
Things You'll Need
- Gardening shears
- Glyphosate herbicide
- Small glass
- Garden sprayer
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.
Fill a small glass with liquid Glyphosate herbicide. Do not dilute the herbicide with water. Doing so will only make it weaker.
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.
Make a mixture of diluted herbicide in a garden sprayer. All herbicides are different, so follow the directions on the package carefully.
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.
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.
- Photo Credit Japanese Garden, Kew image by segantii from Fotolia.com
How to Get Rid of Japanese Knotweed
Japanese knotweed (Polygonum cuspidatum), sometimes called Mexican bamboo, is a shrubby perennial that thrives in U.S. Department of Agriculture plant hardiness zones...
How to Kill Weeds That Look Like Bamboo
That weed in your garden that looks like bamboo is very likely Japanese knotweed. Sometimes called Mexican bamboo, Japanese knotweed grows vertically...
How to Kill Prostrate Knotweed in Lawns
Knotweed is sometimes also called prostrate knotweed because it creeps along the ground rarely achieving more than 4 inches in height. The...
The Best Spray Chemicals to Kill Fleas in the Home
Fleas are tiny pests that invade your home and torment your animals by sucking their blood. Once fleas have started to multiply...