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Spotting Japanese knotweed through the year

How it changes season by season, and the plants Northwich gardeners most often confuse it with.

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Red Japanese knotweed shoots in spring
Spring: red shoots
Japanese knotweed in summer leaf
Summer: full leaf
Surveyor checking a knotweed stand
Not sure? Send a photo

Spring

From about April, red-purple spears with tight rolled leaves come up and can add several centimetres in a day.

Summer

Thick growth reaching two or three metres, with hollow stems flecked purple that zig-zag at each joint, and broad leaves with a flat base.

Autumn

Sprays of cream flowers appear late in summer, before the leaves go yellow and drop.

Winter

Dry brown canes stay standing, hollow and snapping easily, while the rhizome below ground stays alive.

Plants it gets confused with

Bindweed climbs by twining round other plants. Dogwood has woody stems and leaves with curved veins. Himalayan balsam has pink flowers and favours damp riverside ground. If unsure, send us a photo.

The short answers

In brief

What does Japanese knotweed look like?
Hollow, bamboo-like stems with purple or red speckles, growing in a zig-zag from node to node. Leaves are shield or heart-shaped with a flat base, up to about 14cm long. Plants reach 2 to 3 metres in summer.
What does knotweed look like in spring?
Red or purple asparagus-like shoots with rolled-back leaves appear from April. They can grow several centimetres a day.
What does knotweed look like in winter?
The leaves drop and the canes die back to brown, hollow, brittle stems that often stay standing through winter. The rhizome underground is still alive.
What is commonly mistaken for Japanese knotweed?
Bindweed, Russian vine, dogwood, lilac, houttuynia and Himalayan balsam are frequent look-alikes. Bindweed twines around other plants; knotweed stands on its own stems.
Found it?

What happens next

Knotweed surveyWe visit, confirm the plant, measure it and write up what we find.Free knotweed ID from a photoSend a picture and we say what it is. No charge.Knotweed plan for mortgages and salesThe management plan lenders and buyers' solicitors ask to see.Knotweed from a neighbourA dated record of where the stand is and which way it is heading.Knotweed spraying programmeHerbicide applied through the growing season, over several years.Knotweed excavationRemoving the stand and its rhizome in a matter of days.Knotweed root barrierHeavy-duty membrane set upright to keep rhizome on its own side.Knotweed on development landSurveys and removal for Northwich building sites.Knotweed for landlordsSurveys and treatment for rented houses and flats.
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