How is it spread?

Japanese knotweed can produce seeds, but it is extremely rare for these seeds to germinate. The most common method of dispersal is by means of stem, crown and rhizome (underground stem) sections.

New plants will grow from the nodes of pieces of green stem, in soil or water. Mechanical cutters, such as flails, will spread knotweed in this fashion. If stems are dried until they are dark brown, they will not regrow unless the crown (base of the stem) is still attached.

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Flowers

Japanese knotweed can produce seeds, but it is extremely unlikely that they would germinate in the wild.

Stem

New plants can grow from the nodes of pieces of green stem, in soil or water. Machinery such as strimmers or flails will spread it in this way.

Crown

This part is able to survive drying or composting and will rapidly produce new canes when it comes into contact with soil or water.

Rhizome

(underground stem) - pieces as small as 0.7 gramme (smaller than a one pence piece), can grow into a new plant. Breaking up the rhizome stimulates the production of small red buds which each grow into a new stem.

The crown is able to survive drying and composting, and will rapidly produce new canes. If you wish to dispose of knotweed canes by drying or composting, it is important that the stems are cut above the crown, rather than pulling the plant, which will also dislodge the crown. Where local bylaws allow bonfires, canes can be pulled and dried on polythene sheet, before careful burning. Living crowns usually have growth buds and have a characteristic orange/red colouration when cut or peeled, similar to that of rhizome, described below. 

The rhizome (a root-like underground stem) may reach a depth of 3 metres (10 feet) and extend up to 7 metres (23 feet) away from the parent plant. Sections of rhizome as small as 0.7 gramme, or smaller than a one pence piece, can grow into a new plant! Fragmenting the rhizome stimulates the production of small red buds, which grow into new plants. You should never accept topsoil without having first inspected it for rhizome.

© Cornwall Knotweed Forum.

The information on this page has been compiled by the Cornwall Knotweed Forum from information provided by its members and partners. It is provided in good faith to the raise awareness of the issues and to promote best practice in the control of Japanese knotweed. The information may be used freely for private and educational purposes but may not be copied for commercial use. We update information and advice on a regular basis. However the Cornwall Knotweed Forum, or any of its constituent members cannot be held responsible for the efficacy of the treatments described, or any damage to persons, property or the environment that arises from interpretation of the advice given.

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