We will answer the question “How does Japanese knotweed spread?” and also talk about what the plant looks like and what our legal obligations are if we find Japanese knotweed on our land. We will also look at some other important sub-questions, such as “How fast does knotweed grow?” and “How far does knotweed spread?” This information is very important for helping us understand, treat, get rid of, and stop the spread of this invasive weed.
Japanese knotweed is an invasive plant that can cause extensive damage if left uncontrolled. Understanding how this aggressive weed spreads is key to preventing its proliferation. Read on to learn all about how Japanese knotweed reproduces and expands its territory.
First let’s review some background on Japanese knotweed
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Native to Japan, Taiwan and northern China Introduced to Europe and North America in the 19th century.
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Hardy perennial that emerges in spring and dies back in winter. Grows rapidly to heights of 10 feet.
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Features hollow, bamboo-like stems and heart-shaped leaves. Small greenish-white flowers bloom late summer.
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Spreads primarily by rhizomes – underground stems that grow outward horizontally. Very deep and extensive root system.
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Considered an invasive weed due to its rapid spread and damage to foundations, pavements and more.
How Does Japanese Knotweed Spread?
Japanese knotweed spreads vegetatively through its root system and by relocating plant fragments to new areas. It does not spread by seeds in the UK. Its main methods of spread include:
Underground Rhizomes
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The primary way knotweed expands is via rhizome growth. Rhizomes grow up to 3m deep and 7m sideways.
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Any fragments broken off from the rhizome network can regenerate into new plants. Pieces as small as 2mm can regrow if dispersed to a new area.
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Digging out or disturbing the root system spreads knotweed by relocating rhizome fragments.
Stem and Crown Fragments
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Stems, canes and crown sections can also take root if dispersed to new ground.
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Cutting or striking knotweed stands can spread fragments. Must properly dispose of cut pieces.
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Fragments can stick to tools, boots, tires etc. and be transported to uninfested areas.
Intentional Planting
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Originally brought to Europe and North America as an ornamental. Some still sell it.
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Those not recognizing it as a weed may intentionally plant it, furthering its spread.
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Must educate public not to buy or plant knotweed. Proper identification is key.
Soil Movement
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Knotweed commonly spreads when infested soil containing rhizomes is relocated.
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Dumping soil from an infested site can seed new growth if it contains root fragments.
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Using contaminated soil as fill or landscaping material spreads knotweed. Screen soil carefully.
Waterways
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Rhizome fragments are buoyant and can be carried downstream to colonize new riparian areas.
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Major factor in knotweed’s widespread distribution along rivers, streams and drainage ditches.
Vehicles and Footwear
- Soil containing knotweed fragments easily sticks to tires, tracks and footwear and is transported to new sites.
How Quickly Does Japanese Knotweed Spread?
The extensive underground root system of Japanese knotweed makes measuring its exact spread difficult. But above ground growth and spread can be rapid:
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Emerges early spring and grows quickly, up to 10cm per day.
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Can form dense thickets up to 4m tall by late summer. Spreads across open ground rapidly.
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Root system spreads outward up to 7m horizontally from the parent plant and down 3m deep.
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Rhizome fragments as small as 2mm can regenerate into new plants and spread infestation.
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Once introduced to an area, knotweed will quickly spread to dominate if left unchecked.
How Far Can Japanese Knotweed Spread?
Japanese knotweed’s creeping rhizome network allows it to spread indefinately if not controlled:
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Left unchecked, knotweed will travel as far as space and growth conditions allow. No innate limits to spread.
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In the UK, has spread across most of the country assisted by soil movement and waterways.
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Individual infestations limited by proximate pavement, buildings, competing vegetation etc.
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But rhizome fragments leapfrog these barriers when relocated by soil movement or other means.
Does Japanese Knotweed Spread by Seed in the UK?
No, Japanese knotweed does not effectively spread by seed in the UK:
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It is gynodioecious, needing both male and female plants nearby to spread viable seed.
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But only the female variant was introduced to the UK. No male plants are present to fertilize.
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Occasional isolated instances of spread by seed reported, but not typical.
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As seed spread is not a factor, stopping rhizome spread is key to control.
Can Animals Spread Japanese Knotweed?
Animals can potentially spread Japanese knotweed:
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Grazing animals may ingest canes and crown material, later deposited in feces undigested.
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Hoofs, fur and claws could also pick up soil fragments for transport.
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Burrowing creatures like rodents may unearth and redistribute rhizome fragments.
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Not a major vector, but possible, especially where infestations are disturbed.
Can Japanese Knotweed Spread on Shoes or Vehicles?
Yes, shoes, tools, vehicles and more can easily spread knotweed:
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Soil containing minute rhizome fragments can adhere to boots, tools, tires, etc.
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If moved offsite, these fragments can start new infestations wherever knocked off.
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Major avenue of spread during earthworks, demolitions, or any soil disturbance.
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Must have thorough footwear, wheel wash and equipment decontamination facilities onsite.
How to Stop Japanese Knotweed Spreading Further
Stopping knotweed’s spread requires proper identification, treatment and control:
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Learn to identify knotweed and be vigilant in watching for new growth.
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Follow all guidelines for safe disposal of knotweed and infested soil.
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Implement an eradication plan using professional, legal herbicide treatment. May take several years.
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Excavate very small, isolated infestations if feasible. Must properly dispose of all plant parts and soil.
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Use screens, barriers and root barrier membranes to prevent spread to adjacent areas.
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Monitor sites for several years after treatment. Re-treat any regrowth promptly.
With vigilance and persistence, Japanese knotweed’s spread can be halted and eliminated from areas where it has invaded. But stopping its advance requires commitment to safe, effective eradication methods. Don’t allow this aggressive weed to damage your property – take action to evict it!
How does Japanese knotweed spread?
Understanding the origins of Japanese knotweed is key to informing our understanding of its spread in the UK.
Japanese knotweed, which is also called Fallopia japonica, is native to Japan. It was brought to the United States in the 1800s as an ornamental garden plant. Laws have been against it since 1990, though, because it can spread and do a lot of damage to driveways, roads, and home foundations. This legislation seeks to regulate the plant to attempt to control the spread of Japanese knotweed.
Japan knotweed is not a native plant, which helps explain how it spreads and how it is stopped from spreading. As a gynodioecious plant, Japanese knotweed has both female and hermaphrodite forms that need to be close to each other for the seeds to spread. In the UK, this kind of spreading doesn’t happen because only the female form of Japanese knotweed has ever been brought in. Japanese knotweed couldn’t grow and spread by spreading seeds, so it had to find another way to do it, and it has done it very well.
Japanese knotweed is not like many other invasive weeds in that its seeds don’t spread the plant. Instead, the plant’s complex underground root system or stems or crowns do.
Japanese knotweed typically spreads through its underground rhizome, or root, system. When the roots of a Japanese knotweed plant are disturbed, the plant can spread more easily. A new Japanese knotweed shoot can grow from a rhizome fragment as small as 2mm wide. For example, if you have a knotweed plant in your garden, its roots probably go deep into the ground and reach far beyond the height of the plant you can see. If you dig within 7 meters of the Japanese knotweed, you might disturb its root system. You might have found small pieces of Japanese knotweed rhizome in the soil you dug up that you can’t always see. If you move this soil to another part of your garden and leave any stubs of the plant behind, they can grow back very quickly. This will likely lead to another area of Japanese knotweed growth. Because of this, knotweed plants spread quickly, and it’s easy to see how the plant could spread by accident.
We know that Japanese knotweed is a very invasive weed that grows very quickly—up to 10 cm a day. Japanese knotweed is very strong plant, this characteristic has helped to ensure its survival and spread. knotweed’s strong, robust plant structure means it can thrive in a wide range of growing conditions. The plant doesn’t care much about the pH or salinity of the soil; it can grow in temperatures as low as -35°C.
It makes sense that you would want to get rid of this weed from your garden or land, but its complicated underground rhizome network makes it hard to do so yourself. You can’t stop the spread by pulling up the plant; in fact, it might make it spread even faster. Only killing the entire underground Japanese knotweed rhizome system will guarantee the removal of the plant. The Environmental Protection Act of 1990 says that Japanese knotweed is now “controlled waste.” This means that it can only be thrown away in licensed landfills so that it doesn’t spread. Because of how Japanese knotweed grows and the laws that govern it, we suggest that only licensed professionals try to get rid of it.
Can Japanese knotweed spread by seeds?
In its native home of Japan, Japanese knotweed has the ability to spread by seed dispersal. Japanese knotweed is a gynodioecious plant, which means it has both female and male forms that do well in Japan. The two types of weed can spread through their seeds when they are close to each other. This doesn’t happen with UK Japanese knotweed, though, because only the female plant was brought over in the 1800s.
Japanese knotweed doesn’t have any problems spreading because it can’t make seeds. Instead, it spreads quickly when its roots, stems, or crowns are disturbed. When the ground around a knotweed infestation is moved, a knotweed rhizome fragment as small as 2 mm could start a new infestation and spread it.
However, Japanese knotweed can spread much farther because Japanese knotweed seeds don’t help it spread. A seed would only naturally spread in a small area, but soil with a rhizome fragment in it could be dug up and moved anywhere in the country. And because of this, Japanese knotweed is a big problem all over the UK; there aren’t many places where it doesn’t grow.
How does Japanese knotweed spread?
How does Japanese knotweed spread in the UK?
The spread of Japanese knotweed knows no limits. As outlined above, Japanese knotweed seeds are not the cause of its spread in the UK, but rather it is spread through the disturbance of its underground rhizome network.
How does Japanese knotweed grow?
Japanese knotweed exhibits vigorous growth through the soil from a fibrous rhizome (creeping root system, much like underground stems). Soil can be contaminated with reproductive knotweed material up to a depth of 3m and a radius of over 7m (or wider in certain instances) from the main clump of stems. The rate of growth is very rapid.
How fast does Japanese knotweed spread?
The rate of spread of Japanese knotweed depends on the conditions in which it is allowed to grow. In perfect soil and light conditions, rhizomes can spread more than a metre each growing season. How did Japanese knotweed spread around the UK?
Does Japanese knotweed spread through seed dispersion?
Japanese Knotweed can produce seeds, but it does not spread through seed dispersion because it is extremely rare for these seeds to germinate. Despite not being able to propagate via its natural method, Japanese knotweed has been able to spread throughout most of the UK via its stems, roots and crown since its introduction in 1840.