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Japanese Knotweed: Top Weed for Home Damage in North Carolina

This invasive plant can cause damage to your property. Learn about how to protect your home and foundation.

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The North Carolina Invasive Plant Council lists 73 invasive plant species in our state ranging from the air potato to the yellow floating heart. In between are the infamous kudzu and the Japanese knotweed.

While kudzu causes considerable damage to trees, plants, and the environment, it’s the Japanese knotweed that takes on your home. It wreaks havoc on home foundations, driveways, sidewalks, and patios. It finds any cracks or weak spots, growing through them 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, can reach 10 feet tall, and 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 grows fast, spreads rapidly, and it is extremely difficult to eradicate.

How To Identify Japanese Knotweed

The stem is a hollow segmented cane with swollen nodes that’s green with purple speckles. They have a fine white coating that rubs off, and they grow from three to 10 feet tall.

The leaves are bright green with purple speckles, heart-shaped, and grow staggered along the stem. They grow up to six inches long and five inches wide.

Creamy greenish-white flowers form in clusters up to four inches long from late August through September. 

You can find a comprehensive guide to identification, including a video guide, at Knotweed Help

Damage From Japanese Knotweed

In the wild, Japanese knotweed forms a thick layer of stems and leaves that crowd out native plants. It also releases a toxic chemical that inhibits the growth of nearby plants.

Around your home, the roots and stems seek out weak spots, break down and enter those openings, start expanding, and over time, cause considerable damage.

It finds cracks and joints in drainpipes, clogging the pipes and even splitting them. It finds cracks and weak spots in home foundations, widening them, allowing in moisture, and bringing all the damage that causes.

The weed also grows underneath concrete and asphalt driveways, walkways and patios where they find any thin weak spots, growing up through them to find sunlight. They can also break up stone or brick retaining walls. 

Japanese knotweed’s spread causes a huge amount of economic damage. For 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

As you can imagine, getting rid of Japanese knotweed is extremely challenging. There are several steps you can follow that include cutting the stems, removing the clippings to prevent further spread, 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.

Finally, you can consult an expert in eradicating knotweed who has the expertise and 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 office in Charlotte throughout our area. If you find Japanese knotweed on your property, contact the professionals at Dry Pro Foundation and Crawlspace Specialists for a free inspection to ensure the weed has not caused damage to your home.

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