Japanese Knotweed: Top Weed for Home Damage in North Carolina

In North Carolina, kudzu and Japanese honeysuckle rank at the top of the invasive plants listing. Kudzu is found in all 100 counties. Japanese honeysuckle is in 99. These plants take over wild areas, gardens, and lawns, destroying trees and plants. 

However, it is the Japanese knotweed that causes the most damage to homes. It can damage home foundations, driveways, walkways, and patios. It can find any cracks or weak spots, growing through them and gradually expanding and causing still more damage.

What Is Japanese Knotweed?

The Japanese knotweed stem can grow as much as three inches per day and reach up to 10 feet tall. The roots can grow up to 20 feet deep. Its underground network of rhizomes with lateral shoots and roots can spread up to 70 feet from the nearest stem. Further, it can regrow from only a half-inch segment of the stem or rhizome.

All that makes it very difficult to eradicate.

How To Identify Japanese Knotweed

The stem is a hollow segmented cane that gives it the look of bamboo. It’s green with purple speckles. The leaves are bright green and heart-shaped, also with purple speckles, and grow staggered along the stem. 

Creamy greenish-white flowers form in clusters up to four inches long from late August through September. You can find a comprehensive identification guide, including a video guide, at Knotweed Help. 

Damage From Japanese Knotweed

That root growth, spreading underground and out of sight, can find drainpipes and home foundations. They find cracks and joints in drainpipes, clogging and splitting them. They also find cracks and openings in home foundations, widening them, allowing in moisture, and causing significant damage.

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

The Japanese knotweed’s spread causes huge 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 repairing 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, covering the area to eliminate light and water, and placing a plastic barrier 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.

You can also 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 offices in Raleigh and Winston-Salem and throughout the state. If you find Japanese knotweed on your property, contact the professionals at Tar Heel Basement Systems for a free inspection to ensure that the weed has not caused damage to your home.

Holly Richards-Purpura

Content Writer

Holly is a Content Writer for Groundworks who has written and edited web content for the foundation services industry for almost 10 years. With a background in journalism, her passion for the written word runs deep. Holly lives in Columbus, OH, with her husband. Along with educating homeowners, she also has a big heart for the Big Apple.