In spring, Japanese knotweed leaves are a vibrant lime green colour and feature the plant’s distinctive shield shape. They’re arranged alternately and can be up to 14cm long. During this time the stems, or ‘canes’ as they’re sometimes known, will be thin and bamboo-like and clump together to form dense, leafy thickets. The canes grow quickly, typically 10cm per day and by the end of the summer they’ll have reached their full height of between 1.9-3 metres.
By late summer the stems will have changed to a darker, more pronounced green and the foliage will have matured into a more dense, bushy appearance. They’re usually spiky with purple speckles and the nodes are clearly visible on the stems, making them easy to identify. As the weather cools in autumn, the canes will start to turn a reddish/brown colour and they’ll be more brittle.
Once the leaves have wilted and fallen, the rhizomes will become exposed and this is when the plant becomes most difficult to control. If you come across a rhizome while digging or gardening, it’s important that you don’t try to remove it as this could result in the spread of the knotweed. Instead, contact a specialist japanese knotweed leaf shape removal company as they’ll be able to safely and effectively remove the invasive plant from your property.
Although Japanese knotweed spreads mainly by seed, it can also reproduce via its extensive underground root system which is called a rhizome. The rhizomes are able to break off into fragments and, provided they’re in moist soil, can sprout into new shoots which will establish a separate colony of the weed. This is how the plants are so persistent and problematic – even after a single disturbance!
Key identification traits:
Erect, aggressive perennial often found in dense patches due to spread of rhizomes. Hollow, bamboo-like stems up to 6 ft tall with egg shaped leaves arranged in a zig zag pattern at the leaf axils. Flowers are cream coloured and develop in branched sprays at the ends of the stems in August to September.
It is important to recognise the differences between true Japanese knotweed and its close relative, buckwheat (Fagus sachalinesis). While buckwheat has similar characteristics in the early growing season, its leaves are broad and ovate with pointed tips and the stems don’t grow in the iconic zig-zag shape. In addition, buckwheat produces a yellow flower at the end of its stem which is less prominent than the creamy white of Japanese knotweed flowers.