What is Japanese Knotweed?
Japanese knotweed (Reynoutria japonica syn. Fallopia japonica) is a weed that spreads rapidly. In winter the plant dies back to ground level but by early summer the bamboo-like stems emerge from rhizomes deep underground to shoot to over 2.1m (7ft), suppressing all other plant growth.
Eradication requires determination as it is very hard to remove by hand or eradicate with chemicals. New legislation now covers its control – see our Legislation page.
An Invasive Non-Native Species
Japanese knotweed is a fast-growing and strong clump-forming perennial, with tall, dense annual stems. Stem growth is renewed each year from the stout, deeply-penetrating rhizomes (creeping underground stems). Although originally introduced to Britain as an ornamental garden plant, Japanese knotweed is an invasive non-native species.
Rhizomes are creeping swollen root-like structures that are actually adapted stems. Roots, stems with leaves and flowers are produced along its length.
Appearance
In spring, reddish-purple fleshy shoots emerge from crimson-pink buds at ground level. These grow rapidly, producing in summer, dense stands of tall bamboo-like canes which grow to 2.1m (7ft) tall. These canes have characteristic purple flecks, and produce branches from nodes along its length.
Leaves are heart or shovel-shaped and up to 14cm (5½in) in length and borne alternately (in a zig zag pattern) along the stems. The stems die back to ground level in winter, but the dry canes remain for several months or longer.
The creamy-white flower tassels produced in late summer and early autumn reach up to 15cm (6in).
