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Japanese Knotweed: Top Weed for Home Damage in Michigan

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

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The State of Michigan’s list of prohibited and restricted invasive species recognizes 56 species ranging from the zebra mussel to the African oxygen weed. In the middle of that listing is the Japanese knotweed, recognized not only for crowding out native plants but also for damaging property and homes.

It finds cracks or weak spots, grows into and through them, damaging foundations, driveways, sidewalks, and patios. On top of that, it’s extremely difficult to eradicate.


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What Is Japanese Knotweed?

This pernicious, invasive weed 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.

The Japanese knotweed 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 stem closely resembles bamboo, with a hollow segmented cane and swollen nodes that are green with purple speckles. They have 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 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

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

In lawns and gardens near our homes, root growth is the biggest threat. The roots spread underground, find drainpipes and foundations, and enter cracks and weak spots, causing considerable damage.

They further grow under concrete and asphalt driveways, sidewalks, and patios finding weak spots. Then the stems grow up through them seeking sunlight. They can further damage stone or brick retaining walls, breaking them up and causing collapse.

The weed’s spread causes a significant 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

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 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, considerable effort, and cause their own level of damage to your lawn and garden.

You can also consult an expert in eradicating knotweed who has the knowledge and experience to remove the plant without causing further spreading.

We Can Help

We’ve helped homeowners with foundation damage from plants, trees, weather events, and shifting soil in Detroit, Grand Rapids, Traverse City, and Toledo

If you find Japanese knotweed on your property, contact the professionals at FSM for a free inspection to ensure the weed has not caused damage to your home.

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