How To Kill And Control Japanese Knotweed

Fallopian japonica, better known as Japanese knotweed, is a garden weed. It is a highly invasive plant that must be controlled before it spreads and become a significant problem on your property. The Japanese knotweed’s roots are stout and form a robust system that can cause severe damage to driveways, footpaths, and house foundations.

What Is Japanese Knotweed?


The Japanese knotweed is perennial, meaning the plant can live for many years thanks to its deep-penetrating roots (rhizomes) that are more of stems that creep underground, facilitating their rapid growth. The rhizomes are strong enough to penetrate concrete and tar-macadam damaging buildings and various structural surfaces.

The plant produces bamboo-like stems each spring, which grow to a much as 8feet (2.4m) high, suppressing the plants beneath the. Come winter, the stem whither back to the ground. The Japanese knotweed presence in many properties worries many real estate investors and owners, even causing mortgage lenders to withhold loans for affected properties. In some cases, the market value of these properties falls, some by thousands of dollars.

According to research, the plant is believed to have been brought to Britain in the 19th Century touted to be an ornamental plant.  It blossoms in later summer, having vibrant leaves, stout stems, and creamy-white flowers that make it seem very attractive. The Japanese knotweed does not produce seeds; instead, it spreads and grows from even the smallest rhizome pieces. That is why controlling its spread can be challenging but surmountable if done right, which can also see you save money and effort.

Japanese Knotweed Identification

The Japanese knotweed has very distinctive features ranging from hollow green canes dotted with purple speckles and heart-shaped leaves. The stems or canes start appearing in early spring, maturing by early summer. The white flowers develop spikes in late summer. Thus, the plant’s seeds are very rarely fertile and have very little to no impact on how the weed spreads. The Japanese knotweed grows in dense clumps, and its green stems will turn brown in the autumn and remain throughout the winter. Fresh shoots develop around them when spring comes knocking.

Eradicating The Japanese Knotweed

Acting early once you notice the presence of the Japanese knotweed is crucial to mitigating its spread. Start by digging up the weed once you find it; keep in mind the rhizomes (root system) are tough and grows deep; therefore, a pickaxe or something with a similar impact will suffice.

Pieces of the roots are likely to remain and facilitate the plant’s regrowth no matter how careful you are when uprooting the Japanese knotweed. As such, repeating the process severally when you see the regrowth is necessary. It will exhaust the rhizomes’ energy and strength, eventually killing it; however, this might be a long process lasting several years. It is a process best left to the experts at

Legislation On Japanese Knotweed

According to the 2014 Anti-Social Behavior, Crime, and Policing Act, companies and individuals should take the recommended actions to prevent and remove invasive non-native plants like the Japanese knotweed.

After digging up the Japanese knotweed’s rhizomes, you have to contend with the problem of its proper disposal. The plant is classified as “controlled waste” under the 1990 Environmental Protection Act. Moreover, the 1981 Wildlife and Countryside Act stipulates that growing Japanese knotweed in the wild is a criminal act. Therefore, you cannot dump the rhizomes anywhere because studies suggest that topsoil movement can propagate its growth or spread.

The best and most effective way of dealing with Japanese knotweed after digging it up is to dry out and burn the plant.

Killing The Japanese Knotweed

You can kill and keep the Japanese knotweed under control using any weed killer that contains glyphosate. The best time for spraying the weed with the herbicide is during its flowering phase in late summer. But you also will face significant problems because the plant will, at that stage, have developed and reached its full height.

Alternatively, you can spray it when its growth is roughly 3feet or 90cm high, mostly around May. Deal with any regrowth during mid-summer and repeat the treatment in September before the canes start dying down. Conduct a thorough inspection the following spring and repeat the treatment if you discover any signs of regrowth.

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