Japanese knotweed is a very difficult and time-consuming invasive plant to eradicate from gardens and green spaces. It is known for its rapid and vigorous growth patterns and can cause significant damage to the surrounding native vegetation, infrastructure and property. The plant can be recognised by its bamboo-like stems which can reach 2-3 metres in height, as well as by its distinctive creamy-white flowers and deep green leaves which are often adorned with purple speckles. In summer, the plant produces a dense cluster of flowers which can last until late autumn when they fade and the stems begin to die back.
As the rhizomes of Japanese knotweed how to identify japanese knotweed break up, new shoots appear from the ground, growing at an exponential rate and rapidly colonising new areas. The stems of the plant resemble bamboo canes, but are hollow and have distinct rings or nodes with purple speckles and zig-zag patterning at the top of the plant. The leaves are broad, shovel-shaped and can grow up to 14cm (5in) in length, and are usually arranged in a zig-zag pattern along the stems.
It is a common misconception that Japanese knotweed only grows in damp soils, but it actually thrives in many conditions, and can be found across a range of habitats, including low-lying areas, rivers and streams, and on roadside verges and old homes and farms. It is also extremely resilient and can withstand a number of climatic conditions, such as droughts, frosts and heavy rainfall.
Despite this, it can still be very challenging to recognise japanese knotweed. It can be very hard to distinguish from similar plants such as bamboo and kiwifruit, but careful observation of its appearance and characteristics can help to spot the plant. If you are unsure, or you would like to take a more scientific approach, there are free tools and services available which can assist with identification of the plant.
For example, the horticultural industry-backed PictureThis app is an excellent resource which uses image recognition to identify more than 10,000 different plants – including Japanese knotweed – in seconds. It can be downloaded on both Apple and Android devices. If you have a picture of a suspected Japanese knotweed, simply upload it to the app and it will provide you with an instant identification and advice on how to tackle the problem. You can download it here. It is important to be aware that, while having an invasive species such as Japanese knotweed on your own land doesn’t break the law, if it spreads to neighbouring properties or public spaces, it can become a criminal offence, and may result in a fine and/or imprisonment. For more information on this, see our blog post on the legal implications of japanese knotweed.