Japanese Knotweed: Top Weed for Home Damage in the Hampton Roads Area

The Virginia Department of Agriculture and Consumer Services has identified 14 noxious weeds that are regulated by law. They range from the giant hogweed to the distressingly named mile-a-minute weed. There is also the tree of heaven, offset somewhat by the incised fumewort. All these weeds are detrimental to the environment and often to public health.  

There’s yet another noxious weed that not only damages the environment but can seriously damage home foundations, drainpipes, and sewer lines. It’s Japanese knotweed.


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What Is Japanese Knotweed?

 The Japanese knotweed can grow up to three inches per day and reach up to 10 feet tall. It also forms an underground network of rhizomes with lateral shoots and roots that can spread up to 70 feet from the nearest stem. Plus, the roots can grow as much as 20 feet deep. Since it can grow from a half-inch piece of stem, any clippings literally take on a life of their own. 

When it’s growing in your yard, it can damage home foundations, driveways, walkways, patios, drainpipes, and sewer lines. It finds any cracks or weak spots, growing through them, gradually expanding and causing still more damage.

How To Identify Japanese Knotweed 

That fast-growing stem is hollow and segmented, closely resembling bamboo. It’s green with purple speckles with a fine white coating that rubs off. They grow from three to 10 feet tall.

The leaves are bright green with purple speckles, heart-shaped, and grow in a zigzag pattern along the stem. They grow up to six inches long and five inches wide. The plant sheds its leaves as the weather gets cold.

Its greenish to creamy 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

The Japanese knotweed forms a thick layer of stems and leaves that crowd out native plants and take over gardens. They also release a toxic chemical that inhibits the growth of nearby plants.

The wide-ranging rhizome and root growth can also find drainpipes, sewer lines, and home foundations. They enter drainpipe joints and cracks, clogging the pipe, widening the cracks, and even splitting it open. They can further cause significant damage to septic tanks and drain fields.

They also grow underneath concrete and asphalt, finding cracks and weak spots. The stems then grow up through driveways, walkways, and patios expanding the cracks and even breaking up the paved surface.

They can do the same thing with stone or brick retaining walls as well as home foundations. They find any small openings, growing through them, and causing all sorts of damage.

The spread and growth of this invasive weed results in a huge economic cost. As one example, since 2010, New York City has spent more than $1 million on eradication efforts for a 30-acre patch of Japanese knotweed.

That’s an example of the cost of eradicating the weed. There can also be an impact on a home’s value. Lenders are starting to look closely at any infestation before providing a home mortgage. On top of that, there’s also the cost of repair.

How To Protect Your Home

Eradicating the 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 in the soil around the area to stop root spread. 

Another option is to excavate the entire area to at least 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. They can further cause their own damage to your lawn and garden.

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

We Can Help 

If you find Japanese knotweed on your property and causing damage to drainpipes and sewer lines, we can help. 

We operate out of Hampton Roads, Moyock, Elizabeth City, and Virginia Beach.  Contact us at A1 Sewer and Drain to schedule an inspection and repair estimate.


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