Invasive plant - Japanese Knotweed

Invasive plant - Japanese Knotweed

Most people think of animals such as cats and rats when you mention invasive species, however plants can also be invasive. One plant that is particularly damaging in Jersey is Japanese Knotweed (Fallopia japonica). Introduced in the late 1800s, this plant has become so deadly because not only does it penetrate walls, asphalt and drainage works, causing safety risks. But it also forms a dense canopy, which prevents other plants from growing, damaging the islands native plantlife. 

Japanese knotweed can spread and grow very easily, meaning it cannot be controlled through strimming or mowing, in fact, this will likely actually help it spread. For small infestations, it is best to simply pull the knotweed out by hand.

However for bigger infestations, the government advises chemical treatments are best at containing it. If using chemical treatments, ensure to follow the instructions, wear PPE and only use approved herbicides near water. Other methods such as grazing and cutting can reduce the spread of knotweed however it will not eradicate it. Though it is best to get in contact with a company who specialises in Japanese Knotweed removal before starting any work.  

Japanese knotweed can grow from just a small cutting, so it is important that it is properly disposed of. The best method of disposing of knotweed is burning it, you can either do this yourself (of course provided it is safe to do so) or you can bag the knotweed up and take it to the energy recovery facility where they will then incinerate it. Japanese knotweed should never be put with regular green waste as it can hide as seeds and spread to other locations. 

Because this plant has become so out of control, the UK has legislations outlying the codes of practice around Japanese Knotweed. Jersey has laws on this too!  

In Jersey, in 2021 Japanese Knotweed was officially listed as a non-native, invasive species in the Jersey Wildlife Law 2021. This means that it is an offence to possess, deliberatley plant or knowing cause someone else to plant Japanese Knotweed. Only those licenced under law are permitted to plant Japanese Knotweed.  

Sightings of Japanese Knotweed can be recorded on the Jersey Biodiversity Centre website or on the iRecord app. Recording sightings helps to locate where the knotweed problems are most, allowing us to do something about it! 


Photo credit: Raf Fernades 2021

japanese knotweed 2021
Abbi Jones