Japanese knotweed is an invasive and persistent plant that is extremely difficult to remove and control. It can cause damage to buildings, roads and waterways and can deprive native plants of nutrients and sunlight, resulting in their gradual decline. It is important to know how to recognise this weed and keep an eye out for it, especially during the summer months when it grows quickly and can cause a lot of disturbance.
The easiest way to identify Japanese Knotweed how to recognise japanese knotweed is by its bamboo-like stems, which are hollow and dark brown in colour, with green leaves that are heart shaped and arranged in a zig-zag pattern. Its flowers are small and creamy white and appear in dense clusters in the late summer.
These characteristics make Japanese knotweed easy to distinguish from other plants, such as Common bindweed, dogwood and Himalayan honeysuckle, which have similar appearances. Its height is another important identifier, with mature plants growing to a maximum of 2-3 metres high. It is also worth noting that it has purple speckling on its stems and leaves, which is particularly distinctive and a key feature when trying to recognise japanese knotweed.
The roots of a Japanese knotweed plant are known as rhizomes, which work like underground stems and can spread up to seven metres horizontally from the visible part of the plant. These rhizomes are responsible for Japanese knotweed’s relentless growth and resilience. As a result, it is very important to note any evidence of rhizomes or root systems when carrying out work on your garden, land or commercial site, as even the smallest fragments can grow into an entire new plant.
When Japanese knotweed shoots emerge in late winter, they look a little like thick asparagus spears. They then gradually elongate, reaching up to 10cm (30cm) in a few weeks and becoming more obvious as they grow taller. The shoots are able to grow at an astonishing rate, outpacing surrounding plants and growing over them, which can cause damage.
Once the shoots have reached a good height, they produce green leaves that are up to 14cm (5in) wide. Depending on the season, the leaves can be heart-shaped or shovel-shaped and are arranged in a zig-zag formation. If you notice these features on your property, you may have a japanese knotweed infestation.
Once the shoots have finished growing, they begin to die down during the autumn and, in some conditions, they will wither completely, turning reddish-brown or straw coloured. However, even in this stage it can still be possible to spot a knotweed problem as the rhizomes are still active below ground.