If you need help identifying Japanese knotweed, you first must know that Japanese knotweed looks different depending on the current season. These changes can be the cause of misidentifications, leading to future growth and potential property damage. It is imperative that you seek advice from a qualified professional if you believe that you could have Japanese knotweed growing on your property.
Early Spring will see the stem starting to grow, look out for red/purple shoots appearing through the ground.
No matter how small the Japanese knotweed appears on the surface, the rhizome will always be underneath. This is why it is so important to never attempt removal yourself.
During this season the stem will grow rapidly from small shoots into tall canes.
At the beginning you will not be able to see any leaves. As the stem grows the leaves will start to show.
The stem is green with purple speckles, with the leaves being deep green
During the initial growing seasons, the stem may start growing through weak points, in walls, concrete, paths etc. The damage comes from the smaller stems working through cracks
By the middle of Summer the stem will be fully grown. The stems will be hollow with distinctive purple speckles.
Similar to the Japanese knotweed growth above ground, the below rhizomes will be growing rapidly throughout the Summer.
In the Summertime, the stems can reach height of 3 to 4 metres! Growing up to an impressive 10cm a day.
The leaves will now be large, green in colour and either heart or shield shaped.
The leaves will be a deeper green, with the stems becoming browner.
During the Summer is when we will see the most damage. This is because the smaller stems will now be fully grown, creating pressure on any structure the Japanese knotweed is near.
Continuing through Summer, the stems will remain green with purple speckles.
The rhizome will remain bright orange in the middle of the "root."
A stand of Japanese knotweed will cease or slow the growth seen in the Summer months
Later in the Summer, from around August to October, clusters of creamy white flowers will appear.
The leaves will be at their largest, green in colour and have white flowers growing from the stems. The white flowers will now be a main identifying feature through the Autumn months.
The Japanese knotweed canes will turn brown, and have a dark orange centre.
The canes may stay standing throughout the winter months and can occasionally be seen amongst new stands that will grow the following Summer.
As we move into winter the leaves will fall from the plant and the canes will die.
During the winter there will be no leaves and the canes will turn brown.
The rhizome root system is very knotty and woody in appearance. However, if snapped the internal rhizome will appear orange.
The rhizome of a Japanese knotweed plant can remain dormant for up to 20 years.
The depth of the roots can be up to 2 metres, and can spread as far as 7m horizontally.
Regeneration can occur from a piece of the plant as small as 0.7g!
