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Japanese Knotweed: Top Weed for Home Damage in Indiana

Here’s what you need to know about Japanese knotweed in Indiana, from what it is to how to identify it and the damage it can cause to your home.

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The Indiana Invasive Species Council publishes a list of 126 invasive plants in our state. They range from kudzu and field bindweed to buckthorn and crown vetch. 

All these plants do serious damage to our environment. One of the worst in terms of potential damage not only to the environment but to our homes is the Japanese knotweed.


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What Is Japanese Knotweed?

Japanese knotweed grows up to three inches per day in season, reaches up to 10 feet tall, and roots can grow 20 feet deep. The rhizomes can spread up to 70 feet from the nearest stem. 

It can re-grow from a tiny bit of the plant, often as small as a half-inch. Plus, its underground network of rhizomes sends out lateral shoots and roots that can lie dormant for years. All this makes it extremely difficult to eradicate.

How To Identify Japanese Knotweed

The stem is a hollow segmented cane with expanded nodes that resembles bamboo. It’s green with purple speckles and can appear reddish-brown in color. The leaves are bright green and heart-shaped, also with purple speckles. The leaves are staggered along the stem. 

Creamy white tiny one-eighth inch flowers form in plume-like 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 weed forms dense thickets, crowding out native species and reducing wildlife habitat. If that growth is near a stream, even a small portion of rhizome can carry downstream to start new colonies.

If the weed moves into your lawn, the root growth can find drainpipes and home foundations. They enter cracks, widen them, and start splitting the pipes and adding still more damage to the foundation.

They also grow underneath concrete and asphalt, breaking up driveways, sidewalks, and patios, as well as finding their way into stone or brick retaining walls. They again find weak spots and cracks, expanding them and causing considerable damage.

This invasive weed’s spread creates a significant 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 the cost of eradicating the weed. But it doesn’t include the impact on a home’s resale value. On top of that, there’s also the cost of repairing the damage to a home’s foundation, concrete, and lawn.

How To Protect Your Home

There are several steps you can follow to eradicate the weed: Cut the stems, remove the clippings, cover the area with a tarp to eliminate light and water, and place 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. They also pose their own risks of damage to your lawn and garden.

Perhaps the most straightforward way to deal with this weed is to consult an expert who has the experience to remove the plant without spreading it elsewhere in the process.

We Can Help

We’ve repaired foundation damage from plants, weather events, and shifting soil from our offices in Indianapolis throughout the surrounding area. If you find Japanese knotweed on your property, contact the professionals at Indiana Foundation Service for a free inspection to ensure the weed has not caused damage to your home.

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Foundation Repair, Basement Waterproofing & Crawl Space Repair and Encapsulation, Serving Central Indiana & Indianapolis

Indianapolis, IN

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Whiteland, IN 46184