The leaves of Japanese knotweed are bright green and distinctively shield or heart-shaped with a pointed end. They are arranged at staggered intervals along the stem and, unlike many similar-looking plants, do not change colour in autumn. The plant also produces rhizomes in the winter which can grow from tiny sections of root at an alarming rate, often causing damage to drainage and foundations.
As a perennial, Japanese knotweed is a tall shrub with hollow stems that look similar to bamboo. When mature it can reach heights of up to 3 metres. This can be particularly problematic for properties where the plant is growing into a house or other building. In some cases, a property may be subject to a Japanese knotweed abatement order, requiring it to be removed by a qualified invasive species control company.
Identification of knotweed is best undertaken during the spring and summer months, when the plant is at its most vibrant. During these periods the weed’s reddish buds and shoots can be seen sprouting from the ground, growing up to a couple of centimetres a day, outgrowing surrounding plants.
A distinguishing feature of the plant is its understated zig-zag pattern, which can be seen on both the leaves and stems. The purple speckling on the stems, which can be visible even when the plant is dormant in the winter, is another key indicator that you have found a mature Japanese knotweed plant.
Once the leaves have grown to their full size, a distinguishing characteristic of the plant is its clusters of white flowers. The flowers resemble miniature cauliflower heads and can be densely grouped together. The flowers are often visible from a distance, making them an easy-to-spot indicator that you have discovered a mature Japanese knotweed plant.
The flowers will then start to fade, becoming a pale straw colour and eventually falling off the stems as the season comes to an end. This makes it easier to identify the plant as it starts to deteriorate and lose its colour in the autumn. As the weather turns colder, the Japanese knotweed will eventually die back to a brittle, dead straw-coloured cane.
identifying japanese knotweed can be difficult at any time of the year, but it becomes especially challenging in the winter. If the Japanese knotweed has been exposed by blowing winds or being cut and cleared, its brittle hollow stems can still be seen, providing an opportunity to spot the presence of the invasive plant.
While it is true that the plant can be found in a variety of places across the country, it is most often spotted in urban areas and in close proximity to domesticated buildings. If you suspect that you have a Japanese knotweed problem, then it is important to act as quickly as possible, as the invasive plant can cause significant damage to property and land and is very difficult to remove once it has established itself on site. In addition to the potential for property damage, if left untreated, Japanese knotweed can spread rapidly, encroaching into neighbouring garden spaces, properties, drains and paths, and can ultimately damage foundations and other structures.