Japanese knotweed, an invasive plant species native to Asia, is rapidly spreading across the United States, damaging property and threatening home values. This resilient weed can quickly take over landscapes and cause extensive harm if left unchecked.
Some experts say that having this plant on your property could devalue it by 15%¹. Here’s what you need to know.
What Is Japanese Knotweed?
Japanese knotweed (Reynoutria japonica) is a perennial herbaceous plant native to East Asia. It has distinctive heart-shaped leaves, bamboo-like stems with purple flecks, and tall clusters of creamy white flowers that bloom in late summer.
What makes Japanese knotweed particularly problematic is its robust root system of deep rhizomes that are brown outside and bright orange inside when snapped.
These roots allow the plant to grow rapidly, with reddish-purple shoots sprouting in early spring that quickly grow into stems up to 10 feet tall by mid-summer.
While the above-ground portion dies back in winter, the rhizomes survive underground to regrow the following year.
How Does Japanese Knotweed Spread?
Japanese knotweed spreads primarily through its extensive rhizome root system that can extend up to 23 feet horizontally and 10 feet deep.
This invasive species also disperses via stem fragments, which can take root when in contact with moist soil. Remarkably, rhizome fragments as small as 0.025 ounces can regenerate into entirely new plants.
It is often carried to new areas by waterways, on vehicles and equipment, and in contaminated soil. Once established in a new location, it can spread rapidly and be extremely difficult to eradicate.
What Is the Ecological Impact of Japanese Knotweed?
Japanese knotweed forms dense thickets that crowd out native vegetation and reduce plant diversity in the areas it invades. It also alters soil chemistry through allelopathy, potentially inhibiting the growth and reproduction of other plants.
In wetlands and riparian areas, Japanese knotweed reduces habitat quality for wildlife. Its roots do not hold soil as well as native plants, which can destabilize stream banks and increase erosion.
The ecological damage caused by Japanese knotweed is significant and far-reaching, disrupting natural ecosystems and biodiversity wherever it spreads.
How Does Japanese Knotweed Damage Property?
One of the most concerning aspects of Japanese knotweed is its ability to damage buildings and infrastructure. Its strong roots and rhizomes can penetrate concrete, asphalt, building foundations, and walls.
Japanese knotweed exploits existing cracks and weaknesses in structures to cause further damage as it grows. If left unchecked, it can block drains, weaken walls, and compromise the structural integrity of buildings.
What are Effective Japanese Knotweed Control Methods?
Controlling Japanese knotweed requires a comprehensive approach:
- Complete excavation of the plant and its extensive rhizome root system, followed by proper off-site disposal as controlled waste
- Professional herbicide treatment applied over 3-5 years, with visits every 3 months
- Installing root barriers to prevent the spread of this invasive plant to neighboring properties
However, DIY control methods are often ineffective and can actually make the problem worse by inadvertently spreading Japanese knotweed.
What are the Costs of Japanese Knotweed Removal?
Removing Japanese knotweed can be a costly endeavor:
- Professional excavation and disposal fees can range from $15,000 to over $100,000 depending on the size of the infestation (ref)
- Herbicide treatment programs typically cost around $3000-$5000 per year for 3-5 years
- Improper disposal of Japanese knotweed waste can result in fines of up to $5000 plus $1 per square foot of affected property
Given the high costs associated with Japanese knotweed removal, prevention and early intervention are crucial.
Dealing with Japanese Knotweed
As Japanese knotweed continues to spread across the United States, it poses significant ecological and economic risks. This tenacious invasive plant can severely damage buildings, degrade property values, and lead to costly legal repercussions for homeowners.
Effective management requires professional removal methods and proper disposal to mitigate the harmful impacts of Japanese knotweed on properties and the environment.
If you suspect Japanese knotweed on your property, act quickly to have it professionally assessed and treated. Protecting your home and property value from this invasive species requires vigilance and prompt action.
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Nancy has been a plant person from an early age. That interest blossomed into a bachelor’s in biology from Elmira College and a master’s degree in horticulture and communications from the University of Kentucky. Nancy worked in plant taxonomy at the University of Florida and the L. H. Bailey Hortorium at Cornell University, and wrote and edited gardening books at Rodale Press in Emmaus, PA. Her interests are plant identification, gardening, hiking, and reading.