Identification through the seasons
The information below gives a brief explanation of how the appearance of Japanese Knotweed changes throughout the year – it can be most difficult to identify and therefore easily missed during the winter months.
Knotweed in Spring
During March to April, small red/purple shoots (similar to asparagus) emerge from the ground. As time passes, the leaves begin to open, and they can be red or green with red veins.
Knotweed in Summer
This is when the plant grows most quickly – it can easily achieve 10cm per day in the right conditions. The bamboo like green and purple speckled hollow stems will grow in tightly formed stands. The shield shaped leaf with its flat base grows alternatively from zig-zag stems.
Knotweed late Summer
During September to October, the plant begins to flower. Small creamy white flowers, growing on 100mm long stalks, hang down in clusters. Even though the plant does produce seeds there are only female plants here so the plant does not spread through the seeds. You will see the bees enjoying the plant which takes them away from pollinating the native plants that need them.
Knotweed in Winter
After the plant has flowered, the leaves begin to turn yellow, and the plant begins to die back for the winter don’t be fooled though it will almost certainly still be very much alive below the ground. The leaves fall off, and the stems turn brown and become dry and brittle. These dead stems can take up to 3 years to break down.
What is Japanese Knotweed?
As the name suggests, it is native to Japan, and was introduced here in the mid ninteenth century as an ornamental garden plant. Just before the turn of the century, many gardeners’ perceptions changed, and it quickly picked up a reputation as a harmful species, starting to ‘escape’ and spread in the wild.
How can I identify Japanese Knotweed?
The branches and leaves grow in an alternate zig-zag pattern from nodes along the canes. The canes die back during the winter, and turn into a brittle hollow dry winter cane. It can take up to 3 years for the winter canes to break down naturally.
Why is Japanese Knotweed a problem?
It is an incredibly fast growing and strong plant
This bare earth is particularly a problem on watercourses where, during floods, or high tides, the river bank can be eroded away, taking fragments of the plant and its roots and shoots with it, resulting in a the risk of spreading of the Knotweed further downstream.
Even though the plant appears to die back in winter the plant continues to grow underground
Although it spreads much slower, the rhizome can extend in any direction, and will tend to follow the path of least resistance. This can cause problems to homeowners, and it can have a destructive effect on building foundations and drains.
Knotweed can rejuvenate from very small pieces of plant material
Japanese Knotweed has an incredibly sweet tasting nectar
There is the risk that Japanese Knotweed could cause structural damage
As well as helping clients deal with Japanese Knotweed, we also treat other invasive species and general nuisance weeds. Find more information on some of the other invasive species that we can help you with at Other Invasive Species.
If you have an overgrown garden area or green space surrounding your property, please feel free to get in touch. We can assist with all of these problems.
Get in touch and we can help
We’ll help you to identify, tackle and eliminate the invasive species that you have found on your property.