​About Japanese knotweed
Japanese knotweed is a tall perennial plant which originates from Japan.
In Jersey it’s an invasive non-native plant and it can spread in many natural or urban places.
You can find different species of knotweed on the Island:
- Japanese (Reynoutria japonica)
- Giant (Reynoutria sachalinensis)
- Bohemian (hybrid) (Reynoutria Ă— bohemica)
- Dwarf (Reynoutria japonica var. compacta)
All these species are listed as invasive.
Knotweed grows quickly and can spread 5 metres horizontally and 3 metres deep. This can cause serious impacts on the environment, buildings and structures:
- stop native plant from growing
- destroy other species around them
- damage to tarmac and kerb stones
- penetrate drainage works and foundations
- exploit and open cracks and gaps in concrete and walls
Unless you have a licence, it is against the law for you to:
- have or control Japanese knotweed
- plant or allow another person to plant Japanese knotweed in the wild
This also applies for any other of the 3 species of knotweed.
To apply for a licence contact us.
It is your responsibility as a landowner to control the spread of knotweed on your property. If you refuse to take control measures, we can enter into a Species Control Agreement or the Minister can issue a Species Control Order.
Wildlife (Jersey) Law 2021
Japanese knotweed: managing on development sites on GOV.UK
Good Practice Management Guide for Japanese Knotweed on NNNSI
Report your sightings
We gather information on Japanese knotweed to help stop its spread.
To report your sightings of knotweed you can:
You should include photographs and details about the location.
What it looks like
You should be able to easily recognise knotweed at all stages of its growth.
Early season shoots are often asparagus-like and reddish in colour. These grow into tall, hollow, bamboo-like stems which are usually pale green and purple-flecked in the mature state.
Mature Japanese knotweed stems can be 2 metres high and grow up to 10cm per day. Mature plants produce small white flowers in late summer and have leaves that are arranged in a zigzag pattern up the stem. Leaves are shield shaped with a flat base and grow up to 12cm long.
Giant knotweed can grow over 4 metres high, have leaves 15cm to 40cm long and have less zigzag growth. Bohemian knotweed grows to 2 to 3 metres high and has leaves which are heart shaped.
Early season shoots of Japanese knotweed
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Mature Japanese knotweed
Controlling Japanese knotwee​d
You should not control Japanese knotweed by:
This can help it spread because knotweed can regrow from small pieces.
The way to control Japanese knotweed depends on many factors, including location and size. There’s no quick solution and it can take a few years. You must kill their extensive root system to get results that will last.
You should have a written management plan to make sure treatments you apply will work and prevent knotweed from spreading.
You can use some of these measures to control the spread of knotweed:
Using herbicides
The most effective method to control and destroy Japanese knotweed is for you to use a Glyphosate based herbicide.
The best time to apply the treatment is in autumn when the plant is getting ready for winter.
Make sure you carefully read the label, follow the instructions and wear appropriate PPE.
Only use approved herbicides near water.
Cutting shoots
You can weaken and eventually destroy knotweed by cutting and pinching out of all shoots every 2 weeks.
Use a sharp blade to cut shoots and dispose of them carefully.
Occasional cutting may cause more damage by encouraging the plant to spread.
Grazing from livestock
Constant grazing from livestock can reduce the spread but won’t destroy knotweed.
Excavating the site
If you can’t control or destroy knotweed using the above methods, you can dig the site and get the root system out. This will need to be followed by a screening to make sure the whole root system is out.
You must have a licence to excavate knotweed. You should keep the contaminated soil and use:
- a bunding or burial system
- an appropriate root barrier membrane
Trained contractors
You can hire specialist contractors trained in knotweed control. Contact us to ask for the list.
Disposing of Japanese knotweed
Knotweed can regrow from tiny pieces as small as a fingernail, so you must dispose of it carefully.
You must dispose of cut or dead steams by either:
- burning them on site
- piling them up on site and leave them to dry out and die
- bagging them and:
- for small quantities, put them in your household waste
- for large quantities, take them to the Energy Recovery Facility at La Collette to be burnt. Find more information on
harmful plants​
Do not add any pieces to your green waste or take it to the Green Waste at La Collette. Your load will be rejected if it is suspected to contain any of the 4 knotweed species.
Never put pieces in water courses or ditches as it can spread to new areas.
gov.je