How to Identify Japanese Knotweed

Mid-Summer and Autumn

Japanese Knotweed and invasive weeds pushing through concrete

Japanese Knotweed is identified easily during mid-summer and early autumn, where it is at its full annual growth. During spring, reddish shoots appear from the ground and large, asparagus looking spears rapidly grow from bright pink buds. These can grow up to 2cms a day and quickly forming strong bamboo-like stems that grow into green heart shaped leaves.


In summer you can notice the mature Japanese knotweed stems are hollow with purple speckles and can reach up to 3 metres in height. The leaves alternate on each side of the stem producing an obvious zigzag pattern.

By late summer Japanese Knotweed begins to flower, the flowers are white, and appear in long cluster formations. Japanese knotweed spreads via its underground rhizomes (root system) which lay dormant, in the winter months.


The rhizomes can spread 7 metres outwards from the visible growth, and to depths of up to 3 metres. Japanese Knotweed can spread from even a small fragment of rhizome being accidently carried to another area, even by disturbing the soil several metres from where the stems appear.

As Japanese Knotweed very rarely grows from seeds, it is evident that the plant is incredibly invasive which has been spread to most parts of the UK, simply through the translocation of rhizomes fragments in contaminated soil.