Identifying Japanese Knotweed Roots

Identifying Japanese knotweed roots is essential for property owners and green spaces managers as this perennial weed can cause damage in gardens and commercial sites. Despite appearing to die back in the winter, Japanese knotweed continues to spread throughout the year from its underground stems (known as rhizomes) and if left unchecked it can grow into dense, tall bamboo-like shoots up to 7ft high. identification japanese knotweed roots of the plant at all times is therefore essential and there are a number of things to look out for. This article will highlight how to recognise Japanese knotweed during each season with tips on its leaves, flowers, stalks and roots.


Japanese knotweed starts to emerge from its winter dormancy in early spring. During February, March and April, the reddish buds on the stems turn into shoots that can grow a couple of centimetres each day. As the shoots mature, they begin to form branches from nodes on their length and form dense bamboo-like clumps that can be up to 2.1m (7ft) tall. The leaves of the plant are shield or shovel shaped, up to 12cm long, and can be either a dark green colour or with purple specks.

At the end of the summer, Japanese knotweed develops clusters of creamy white flowers that are up to 5cm in diameter. These flowers are crowded together on the top of the stalks and provide a valuable source of late-season pollen. After the flowering period, the stalks become brown and brittle, and the leaves gradually lose their colour. The rhizomes then slowly move deeper into the ground until they are hidden from view in the autumn.

Identification in the Winter

In the winter, identifying Japanese knotweed can be more difficult. As the weed goes into dormancy, the canes that were visible above ground in the summer will dry up and turn straw coloured. However, a Japanese knotweed infestation is still alive and thriving underground in the rhizomes and it is only when the shoots appear again in the spring that people realise there is a problem.

When the first frosts hit, the rhizomes of the plant will begin to change colour. They will eventually become a rich orange or yellow colour before they become completely brown and brittle. The leaves will also turn from a fleshy green to a dark brown or orange colour and the whole plant will begin to die back. During the winter, anyone who is digging or working on a site may come across fresh Japanese knotweed roots. These roots are distinctive due to their rounded shape, tapered tip and the fact they are hollow inside, resembling carrots. If you come across these, it is important that you seek expert advice as they are a sure sign that the area is infested with Japanese knotweed. A specialist will be able to remove the roots and ensure that the problem is eradicated.