Minnesota lists 29 prohibited noxious weeds ranging from Palmer amaranth to poison hemlock and Canada thistle to wild parsnip. North Dakota lists 13 noxious weeds, including salt cedar and yellow toadflax.
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 Japanese knotweed. It is included on the Minnesota list and appears throughout the state. It’s expected to move into North Dakota over the next few years.
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What Is Japanese Knotweed?
The Japanese knotweed 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.
When it’s growing in your yard, it can damage your home’s foundation, driveway, patio, and walkways. It finds any cracks or weak spots, growing through them, gradually expanding, and breaking up the concrete or asphalt.
How To Identify Japanese Knotweed
It is a shrub-like plant with hollow stems with slightly swollen nodes, which gives it the appearance of bamboo. The stems are green with purple speckles. The leaves are bright green with purple speckles growing between two and six inches in length with a pointed tip. The leaves alternate along the stem.
The tiny flowers are greenish-white to creamy white in clusters up to four inches long. It blooms 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 dense thickets valued by gardeners for landscape screening crowd out native species and reduce wildlife habitat. Plus, it doesn’t stop with a small patch, it grows and spreads widely through the rhizomes. If any portion of the plant is washed into a nearby river or creek, it moves downstream and starts growing in new places.
If Japanese knotweed finds your lawn, the root growth seeks out drainpipes and home foundations. They enter any cracks or push on weak spots, clogging and splitting pipes, and damaging the home’s foundation.
And they don’t stop there. They grow under concrete and asphalt driveways and walkways, finding cracks and starting the destruction process. They can also do significant damage to retaining walls.
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
Eradicating the Japanese knotweed is extremely difficult. 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 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 level of damage to your lawn and garden.
Yet another approach is to consult an expert in eradicating knotweed who has the skill and experience to remove the plant without spreading it.
We Can Help
We’ve repaired foundation damage from plants, weather events, and shifting soil from our offices in Fargo, Minneapolis, Rush City, Sioux Falls, and throughout the surrounding area.
If you find Japanese knotweed on your property, contact the professionals at Innovative Basement Authority for a free inspection to ensure the weed has not caused damage to your home.