How To Correctly Identify Japanese Knotweed

Japanese Knotweed is an invasive non-native plant pest and is considered one of the most problematic plant species in the UK and Ireland. This is mainly due to its highly invasive nature and its extremely rapid growth rate. The species was introduced to Britain in mid-19th century as an ornamental plant for large gardens, prized due to its imposing size and sprays of creamy white flowers.

Identifying Japanese Knotweed

Japanese Knotweed plants have a Creamy white colour, 0.5cm wide. It forms clustered panicles that can grow to 10cm and bloom in the very late summer around August/September time. The stem of the plant grows in zig-zag pattern, with green, purple and red speckles visible on the cane itself. The cane is hollow and grows to 2-3 metres in height. Can Grow up to 2cm a day. Japanese Knotweed leaves are a light green with red or purple flecks. Heart or shovel-shaped with a pointed tip and shoots out from nodes in a zig-zag pattern. New leaves are rolled up with dark red veins, mature leaves can grow up to 20cm. Japanese Knotweed can grow up to 10cm per day during late spring / early summer, with the plant typically growing up to 2.1m (7ft) but can grow up to 3m (9.8ft).

Japanese Knotweed is a self-propagating plant, meaning that it spreads and grows from fragments of the plant itself. Japanese Knotweed has an extensive underground rhizome system and if you were to snap a piece of the rhizome you would see that inside of Japanese Knotweed rhizome is a bright orange colour and this is how we are able to determine whether plant is in fact Japanese Knotweed.

Dead canes of Japanese Knotweed can also be mistaken for doc plants and vice versa, with the dead cane looking woody. Mature canes of Japanese Knotweed are thick and strong like bamboo.

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