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Japanese Knotweed: Top Weed for Home Damage in Ohio

Japanese knotweed is an invasive plant that can cause damage to your Ohio property. Learn how to identify it and how to protect your home and foundation.

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Ohio has 31 plants on its official prohibited noxious weed list, ranging from kudzu to Canada thistle to the chillingly named mile-a-minute weed. While all these weeds are, by definition, especially difficult to control and remove, the Japanese knotweed stands out.

It can not only take over large areas crowding out other plants, but it can also damage home foundations, driveways, walkways, and patios. It finds any cracks or weak spots, growing through them gradually expanding and causing still more damage.

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What Is Japanese Knotweed?

The Japanese knotweed can grow up to three inches per day, reaching between three and 10 feet tall. The roots can grow as much as 20 feet deep. On top of that, the rhizomes can spread up to 70 feet from the nearest stem. Then there is its ability to regrow from as little as a half-inch segment of stem, root, or rhizome.

It has the distinction of being listed in the Top 100 World’s Worst Invasive Alien Species. It can grow. It can spread. And it’s not very choosy about where. All that makes it very difficult to eradicate.

How To Identify Japanese Knotweed

The leaves are bright green with purple speckles and are heart-shaped. They grow staggered along the stem.

The stem is green with purple speckles but is often described as reddish-brown. The hollow segmented stems resemble bamboo. 

From late August through September, creamy white flowers form in clusters up to four inches long. Knotweed Help has provided a comprehensive identification guide, including a video. 

Damage From Japanese Knotweed

As with any invasive non-native plant, the Japanese knotweed can take over a large area in the wild, crowding out native species. If it finds its way into your lawn or garden, the roots and stems can find cracks and joints in drainpipes, clogging and splitting them. 

They can also find cracks and openings in home foundations, widening them, allowing in moisture, and starting all the damage that can cause.

They also grow underneath concrete and asphalt driveways, sidewalks, and patios where they find any weak spots, growing up through them seeking sunlight. They can further find stone or brick retaining walls, breaking them up. 

The Japanese knotweed’s spread causes a significant amount of economic damage. As only one example, since 2010, New York City has spent more than $1 million on eradication efforts for a 30-acre patch of Japanese knotweed.

If it finds its way into your lawn, it can also impact your home’s resale value. That’s on top of the cost of repair and eradicating the weed.

How To Protect Your Home

Eradicating the Japanese knotweed is extremely difficult. There are several steps you can follow that include cutting the stems, removing the clippings, covering the area with a tarp to eliminate light and water, and placing a plastic barrier in the soil around the area to stop root spread. 

Another option is to excavate the entire area, at least to a depth of 20 feet. You can also try a glyphosate-based herbicide, the main ingredient in Roundup. All these approaches take time and considerable effort. Plus, there are a few long-lasting effects from either the herbicide or the excavation.

You can also consult an expert in eradicating knotweed who has the experience to remove the plant without spreading it elsewhere in the process.

We Can Help

We’ve helped homeowners with foundation damage from plants, trees, weather events, and shifting soil from our offices in Cincinnati and Columbus, as well as surrounding areas.If you find Japanese knotweed on your property, contact the professionals at Ohio Basement Authority for a free inspection to ensure the weed has not caused damage to your home.

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