Japanese Knotweed
Perennial & invasive weed
Japanese knotweed is an extremely invasive perennial requiring careful identification and specialist management. It can force through neglected ground, dominate borders and spread from very small pieces of underground stem. Do not treat it as an ordinary garden weed. Early professional or specialist advice is sensible, particularly where it is near boundaries, buildings, water or development work.
How to identify it
New shoots emerge in spring as reddish, asparagus-like spears. By summer, bamboo-like hollow reddish canes with obvious joints form dense stands 2-3 m tall. Broad, shovel-shaped leaves are arranged in a zig-zag along the stems and have a squared-off base. Sprays of small creamy-white flowers appear in late summer. In winter, dead canes turn brown and persist. The extensive orange-brown rhizome system spreads underground and can regrow from tiny fragments.
Where it grows
It grows most strongly from spring to autumn on disturbed ground, neglected corners, stream banks, railway land and garden boundaries, but can establish almost anywhere. In UK gardens it may arrive in imported soil, from neighbouring land or after careless movement of plant material. Winter dieback can hide the problem until new red shoots appear in spring.
Why it is a problem
Japanese knotweed forms dense shade that excludes other plants and its rhizomes can spread far beyond the visible stems. Tiny fragments can create new infestations. There are legal restrictions on allowing it to spread and on disposal; affected material is classed as controlled waste. Moving soil or cut stems casually can therefore worsen the problem and create legal difficulties.
How to control it
Identify it carefully and seek professional or specialist advice before disturbing an established patch. Do not dig and move it, rotavate it, fly-tip it, or put it in home compost or green-waste bins. Avoid cutting or transporting stems unless following an appropriate disposal plan. Mark the area, prevent accidental soil movement and keep records or photographs of seasonal growth. Physical control needs specialist planning and persistent follow-up because every rhizome fragment must be contained; consult the RHS or a local garden centre for suitable local guidance.
Commonly confused with
It is sometimes confused with giant knotweed, Himalayan knotweed, dogwood or young bamboo. Japanese knotweed has hollow jointed canes, a zig-zag leaf arrangement and broad leaves with a distinctly squared-off base. Bamboo has narrower leaves in clusters, while dogwood's stems are woody and its leaves are arranged in opposite pairs.
Japanese Knotweed: frequently asked questions
How do I identify japanese knotweed?
New shoots emerge in spring as reddish, asparagus-like spears.
How do I get rid of japanese knotweed?
Identify it carefully and seek professional or specialist advice before disturbing an established patch.
Where does japanese knotweed grow?
It grows most strongly from spring to autumn on disturbed ground, neglected corners, stream banks, railway land and garden boundaries, but can establish almost anywhere.
General guidance for UK gardens and allotments, focused on prevention and non-chemical control. For a confirmed identification, the RHS or a local garden centre can help. Page updated 19 Sep 2026.