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We have a new yard. Our grass was seeded last April. The grass is coming in and we have this weed that some people said cannot be killed. It is easy to pull up when small but once the plant gets larger, the root is very hard to get out of the ground. Can you please give us advice on how to get rid of this ugly and invading plant? Charley

Answer

We have a new yard. Our grass was seeded last April. The grass is coming in and we have this weed that some people said cannot be killed. It is easy to pull up when small but once the plant gets larger, the root is very hard to get out of the ground. Can you please give us advice on how to get rid of this ugly and invading plant? Charley What you are dealing with is Japanese Knotweed, Fallopia japonica or Polygonumcuspidatum, a terribly invasive plant that has swept across the majority of the US, Canada and UK. It is native to Eastern Asia and was brought here in the 1800s as an attractive ornamental planting. Once Japanese Knotweed gets established it is virtually impossible to get rid of, but with hard work and vigilance you can successfully keep it under control.

Japanese Knotweed is a perennial that emerges from the ground in the spring and forms in large colonies created by the rapid growth of rhizomes, which are underground stems. The above-ground colonies are generally so dense that you almost never see any other native plant because they are crowded out. It can grow 10 feet tall and has leaves that look like spades up to 5-6" long. The stems, which grow annually and die back in the winter, are bamboo-like and a reddish-brown color. Japanese Knotweed can sprout from extremely small pieces of rhizomes left behind after you pull it out of the ground. Moving soil that has had Japanese Knotweed growing in it will spread it from one part of your property to another.

The stems are hollow and segmented and the leaves and stems have a waxy coating to protect from chemical sprays, so herbicides have a minor effect on the plant. I have found that the best way of controlling Japanese Knotweed is to remove it as soon as you see it beginning to show up in an area, because once it's established it becomes much more difficult to remove. I use a combination of carefully pulling it up by the roots and then repeated cutting of the re-sprouts throughout the season. Eventually this method will greatly suppress the plant's natural photosynthesis process and deplete the rhizomes of their energy. Several cautions: 1) this is a long-term process that will require your persistence, 2) even the smallest piece of the plant will re-sprout, so be very careful where you put the plants you remove. They must be bagged and put out in the garbage for incineration, and 3) never put the removed plants in your compost pile and never take them to a public landfill; they will spread all over.

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About Linda Lillie

Linda K. Lillie is the President of Sprigs & Twigs, Inc, the premier landscape design and maintenance, tree care, lawn care, stonework, and carpentry service provider in southeastern Connecticut since 1997. She is a graduate of Connecticut College in Botany, a Connecticut Master Gardener and a national award winning landscape designer for her landscape design and landscape installation work.

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