How to identify Japanese Knotweed

Here’s what to look out for...

Leaves

Knotweed leaves

The leaves are green, shield or heart-shaped, with a flat base and are up to 12cm long.

  • Shield shaped
  • Flat base
  • Lush green colour in summer
  • Form zig-zag shaped stems

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Main Stems

Knotweed purple specs on stems

The stems are green with red or purple specks, hollow and similar to bamboo, and can grow up to 2- 3m tall, forming dense cane-like clumps.

  • Purple speckles in Spring/Summer
  • Regular nodes (like bamboo)

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Roots (Rhizome)

Japanese Knotweed roots

The roots consist of rhizomes, which are yellow / orange when cut, but can spread to a depth of 3m and radius of 7m.

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Flowers

Japanese Knotweed flowers

Clusters of creamy flowers appear on the tips of most stems from August to October but produce sterile seeds.

  • Late summer / autumn
  • Spike length can be 10cm

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What to look for in Spring

Knotweed purple specs on stems

In the spring, Japanese Knotweed emerges from winter dormancy with new leaves initially being reddish in appearance with an arrow shaped tip up to 4cm long.

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What to look for in Summer

Knotweed purple specs on stems

2-3 metre stems, which are hollow with nodes that resemble bamboo. The leaves will be green in colour appearing from zig-zag plant growth. In late summer the plant will start to produce white flowers.

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What to look for in Autumn

yellow leaves in autumn

Similar to late summer, approaching late autumn the leaves start to go yellow and start wilting, this is a sign of the plant starting to pull all the nutrients from above ground.

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What to look for in Winter

Knotween winter

Japanese Knotweed canes will begin to die back and the plant will lose its leaves, leaving dried brittle canes. 

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Identification Service





If you suspect Knotweed but are unsure, use our free Identification Service. Simply send us a photo and we’ll get back to you.

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