Identification

General description:

Japanese Knotweed flowers between late summer and early autumn, producing creamy white flowers that form in clusters. The leaves on the plant are light green while the stems can have red or purple flecks. The leaves are heart or shovel-shaped with a pointed tip, and shoot out from nodes in a zig-zag pattern. The stem of the plant grows in a zig-zag pattern, is green with purple and red speckles, and can grow up to 2-3 metres in height. The roots of the plant, also known as rhizomes, are dark brown on the outside and orange/yellow on the inside. The information below will hopefully inform you of Japanese Knotweed and its identification within the UK.

Photo 100029437 | Japanese Knotweed © Natalie Schorr | Dreamstime.com

Late spring – summer (vegetative stage)

This describes the period after dormancy when the plant will not have flowers, during this stage the leaves will be quite large, around 15 cm long and 10 cm wide, and heart/saddle shaped. The leaves are pointed at the end and are light green, they come out of the stem on alternating sides, with the stem in a zigzag pattern. The stem may have red or purple speckles. Below you can easily see the leaf during this period as described above.

Photo 168646264 | Japanese Knotweed © Trygve Finkelsen | Dreamstime.com

Above are Japanese Knotweed stems, you can see their red and purple speckles, also note the stems are bamboo like.

Summer – early autumn (flowering)

Japanese Knotweed will look very similar during this period and the ‘vegetative stage’ while the plant is growing, the difference is that it will now have flowers as well. Japanese Knotweed flowers are Cream white in colour, around 0.5cm wide, and form clusters that can each grow to 10cm. Blooms very late summer (August/September). Below you can see a picture of this! further below you can see what this looks like as part of the whole plant, with the flowers growing along each branch.

Late Autumn – Spring (Dormancy)

Japanese Knotweed is a deciduous plant, this means that over the winter its leaves will die off and only its stem and roots will be left, until it grows back the next spring. Due to its lack of flowers and leaves, Japanese Knotweed will be harder to recognise during this time, however I will give you some tips below.

You may be able to recognise the knotweed from its roots and rhizomes, these are shown below, they are dark brown with a yellow centre. remember to take caution, as even 1cm of rhizome or root can sprout a new plant.

The image below shows Japanese Knotweed beginning to grow during spring.

The next image shows flowering Japanese Knotweed: