Japanese Knotweed: Top Weed for Home Damage in Northern Ohio

Ohio keeps close tabs on invasive noxious weeds. In fact, the state has established by law a full listing of prohibited noxious weeds. As you might expect, there are quite a few notorious weeds on that list, from various thistles to poison hemlock. They all crowd out native species and cause considerable damage in the wild.

Japanese knotweed does all that and it further damages home foundations, driveways, patios, and walkways. It does this by finding any weak spots or cracks, growing through and into them, and breaking up concrete and asphalt, causing considerable damage. 

What Is Japanese Knotweed?

Japanese knotweed’s stems can grow up to three inches per day, reaching between three and 10 feet tall. Its underground rhizomes can reach as far as 70 feet from the nearest stem. Then there’s the roots that can grow as deep as 20 feet, making it very tough to dig up without leaving roots that can continue to grow. If that kind of growth isn’t enough, it can regrow from as little as a half-inch of stem, rhizome, or root. 

It has the distinction of being listed in the Top 100 World’s Worst Invasive Alien Species. It can grow. It can spread. And all that makes it very difficult to eradicate.

How To Identify Japanese Knotweed

It’s a reasonably distinctive plant with bright green heart-shaped leaves with purple speckles. The leaves are four to six inches long and three to four inches wide. They grow staggered along the stem.

The stem is hollow and segmented by swollen nodes, resembling bamboo. It is green with purple speckles and can appear reddish-brown. 

From late August through September, creamy white tiny one-eighth inch flowers form in plume-like clusters up to four inches long. You can find a comprehensive identification guide, including a video at Knotweed Help.

Damage From Japanese Knotweed

In the wild, the weed forms dense thickets that crowd out native species, reducing wildlife habitat. And it doesn’t stop; it continues to spread particularly near streams that can carry pieces of rhizomes downstream to form new growth.

If the plant moves into your lawn or garden, the roots and stems can do considerable damage to drainpipes, clogging and splitting them. They can also find their way to your home’s foundation where they grow into any cracks or weak spots. This not only starts breaking up the foundation but also lets in moisture, bringing with it pests, mold, and rot. 

Japanese knotweed can also grow under asphalt and concrete driveways, patios, and sidewalks. They then repeat the process of finding any cracks or weak spots breaking up the surface. 

There is a significant amount of economic damage from all this growth. For example, since 2010 New York City has spent more than $1 million on eradication efforts for a 30-acre patch of Japanese knotweed.

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

Getting rid of Japanese knotweed is extremely challenging. As it grows and embeds itself in your lawn, the challenge only gets worse.

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 to a depth of at least 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. They will have 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 Cleveland throughout the surrounding areas.

If you find Japanese knotweed on your property, contact the professionals at Ohio Basement Systems for a free inspection to make sure the weed has not caused damage to your home.