Japanese Knotweed

Biological Name:

Japanese-Knotweed: Polygonum cuspidatum

Natural Habitat:

Japanese knotweed, or Fallopia japonica, is a type of flowering plant that is native to Japan, China, and Korea. It grows in a variety of habitats, including forests, fields, and along roadsides and streams.

Description:

Japanese-knotweed is a type of flowering plant that is commonly found in fields and other grassy areas. It is a member of the Polygonaceae family which also includes plants such as rhubarb and sorrel. Japanese-knotweed is an annual or perennial plant that produces small white or pink flowers and clusters of seeds. The plant is often used as a cover crop to improve soil health and suppress weeds. It is also known for its ability to tolerate a wide range of growing conditions including wet or dry soils. In some areas Japanese-knotweed is considered a weed because of its ability to invade cultivated areas and cause allergies and other health problems.

Frequently Asked Questions (FAQs)

Q: What is the problem with Japanese knotweed?
A: In its drive to expand, Japanese knotweed will exploit existing weaknesses in property underground services, walls, concrete, foundations, fences, out-buildings and conservatories. As it grows and expands, it will crack walls, ruin garden fences and it can even break through into buildings.
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Q: Why should you not cut Japanese knotweed?
A: If you do find Japanese knotweed on your property it is most important that you prevent further spread of the plant. Do not strim, cut, flail or chip the plants as tiny fragments can regenerate new plants and make the problem even more difficult to manage.
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Q: Is Japanese knotweed a big deal?
A: Although Japanese Knotweed is not dangerous to humans or animals, its ability to relentlessly grow up to 10cm a day can cause tremendous damage to your property. For instance, it can cause the following problems: Significant structural damage to weak points in masonry and property foundations.
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Q: What will choke out knotweed?
A: Spring is the beginning of the Japanese knotweed’s growth season, so smothering it with a tarp and keeping it tamped down with heavy rocks can ultimately kill the plant. To smother Japanese knotweed, cut all the tall stems as close to the ground as possible. Then, remove debris from the area the knotweed grows in.
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Q: Can I sell my house if I have Japanese knotweed?
A: Can you sell a property with Japanese Knotweed? You can sell a property with Japanese Knotweed; however, you may need to take some extra measures to ensure that potential buyers feel comfortable purchasing the house and confident that they will be able to secure a mortgage from their bank.
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Q: Can you burn Japanese knotweed?
A: Can I Burn Japanese Knotweed? You can but you must do this with extreme care. When the knotweed material has been excavated, cut the stems and leaves and leave it to dry before burning it, ideally without contact with the soil.
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Q: Does Roundup work on Japanese knotweed?
A: Glyphosate based products, like Round Up, are effective against japanese knotweed. These herbicides can either be sprayed onto the leaves or injected into the stem of the plant. The plant should be sprayed with weed killer at several stages during its growth.
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Q: What does Japanese knotweed do for your body?
A: Herbalists use Japanese knotweed to reduce plaque, gum pain, and gingivitis, claiming it has anti-inflammatory properties. Additionally, emodin is a natural compound in Japanese knotweed roots that serves as a natural laxative.
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Q: Is Japanese knotweed poisonous to humans?
A: Is Japanese knotweed poisonous? Japanese knotweed is not poisonous and is not harmful to touch, however, always use caution to avoid inadvertently allowing the infestation to spread.
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Q: Does Japanese knotweed give you energy?
A: Incredibly, scientists have found that the powerful antioxidant and health giving compounds in knotweed rhizomes, such as resveratrol, are also responsible for the plant’s ability to generate massive amounts of energy.
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Q: Can Japanese knotweed be eaten?
A: They are tart, crunchy, and juicy; can be eaten raw or cooked; and can lean sweet or savory, depending on how they’re prepared. So knotweed is in many ways the perfect thing to forage: It tastes good, it’s easy to find, and, unlike many wild edibles, it’s at zero risk of being over-harvested.
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Q: What is the difference between knotweed and Japanese knotweed?
A: One of the most identifying features of the Knotweed are the leaves. Japanese knotweed leaves are shovel-shaped (not to be confused with heart-shaped) with a point at the tip and staggered on the stem (one stem per node), creating a zig-zag stem growth pattern which is quite characteristic.
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Q: Is Japanese knotweed anti-inflammatory?
A: Anti-Inflammatory and Antiviral Activity. Some bioactive compounds from the extracts of Japanese knotweed exhibit anti-inflammatory and antiviral activities. The anti-inflammatory and protective activities of P. cuspidatum on Dry Eye Disease (DED) was investigated by Park et al.
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Q: Is knotweed serious?
A: Japanese knotweed can do extensive damage if left untreated. While it can’t grow through bricks and concrete, it can work its way through small cracks and gaps. It can cause damage to foundations, patios, walls and more if ignored. This is why mortgage lenders take it seriously.
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Q: How do I get rid of Japanese knotweed?
A: Spraying or injecting the stems with chemicals can be an effective treatment to stop knotweeds spreading. You must only use approved herbicides. You’ll have to respray. It usually takes at least 3 years to treat Japanese knotweed.
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Q: Should I pull out knotweed?
A: The plant will not resprout from the cut cane, but removing them may aid in finding and treating resprouts in an infested patch. The area will also be more conducive to revegetation if the cut canes are removed. Glyphosate concentrate- Glyphosate is a non-restrictive use herbicide.
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Q: Should I dig up Japanese knotweed?
A: Regardless of the season, digging out the roots of Japanese knotweed can discourage new growth and help to eradicate the plant. This method, while mostly effective, can and should be used in combination with another.
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Q: Can Japanese knotweed be permanently removed?
A: Physical Removal – Excavation and removal of the underground root and rhizome system, ensuring Japanese knotweed is gone, and gone for good. Herbicide Treatment – Is a control method, as while herbicide can kill immature plants, it’s less effective on mature rhizomes, often causing dormancy rather than death.
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Q: What kills common knotweed?
A: Roundup, Gallup, Landmaster, Pondmaster, Ranger, Rodeo, and Touchdown are all herbicides recommended to kill Japanese Knotweed. They are all glyphosate-based herbicides and will kill the troublesome weed. The best time to spray the leaves of Japanese Knotweed with herbicide is late summer or early autumn.
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Q: What can I do if my Neighbour has Japanese knotweed?
A: What to do if your neighbour has Japanese knotweed? If your neighbour has Japanese knotweed, then you should tell them as soon as possible. If they do not arrange to have the Japanese knotweed treated and allow the Japanese knotweed to spread to your land, then you may able to bring a claim against them.
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Q: Is Japanese knotweed in BC?
A: As in Britain, Japanese knotweed in North America bears only female flowers, and thus is sterile. Both types of Bohemian knotweed plants occur in British Columbia and elsewhere in the Pacific and Inland Northwest. Those Bohemian knotweed plants having perfect flowers produce pollen, and thus can produce seed.
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Q: Can you touch knotweed?
A: Is Japanese knotweed poisonous? Japanese knotweed is not poisonous and is not harmful to touch, however, always use caution to avoid inadvertently allowing the infestation to spread.
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Q: How did I get Japanese knotweed in my garden?
A: A small fragment of Japanese knotweed rhizome may have found its way into your garden (e.g. in a batch of contaminated soil, or carried on someone’s shoes) and grown into a new plant. If Japanese knotweed was growing on your property in the past, it may be that it was dormant for some time and has only re-emerged now.
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Q: Who kills knotweed?
A: Roundup, Gallup, Landmaster, Pondmaster, Ranger, Rodeo, and Touchdown are all herbicides recommended to kill Japanese Knotweed. They are all glyphosate-based herbicides and will kill the troublesome weed. The best time to spray the leaves of Japanese Knotweed with herbicide is late summer or early autumn.
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Q: What can I do if my Neighbour has knotweed?
A: If your neighbour has Japanese knotweed on their property, they are under no legal obligation to remove Japanese knotweed from their own property. However, if it starts to encroach upon your property they are causing a private nuisance and therefore are open to court action.
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About the author

Samuel is a gardening professional and enthusiast who has spent over 20 years advising homeowners and farm owners on weed identification, prevention and removal. He has an undergraduate degree in plant and soil science from Michigan State University.