Japanese knotweed can easily be identified at any time of year provided that you know what to look for; here we explain the common identifiers of Japanese Knotweed Weed.
We also provide links to our information sheets and brochure, which all provide pictures and descriptions for Knotweed identification. The 5 easy ways to identify Japanese knotweed are:
1) Spade shape leaf: Knotweed is sometimes described as heart shaped but the base, where the stem joins the leaf is very flat and thus we believe the leaf is best described as spade shaped – like the spade on a playing card. The leaves grow on alternate sides of the stem.
2) Zigzag stem: A common characteristic of Japanese knotweed is the growth habit of the stems. They grow in an understated zigzag pattern which is particularly visible on mature plants that are 1.8-3metres tall. Provided the plant is not cut back the stems also will be visible in the winter. Although as they die back, the stems turn into dead hollow canes but still retain the zigzag habit.
3) Orange tinge to the roots: The roots, known as rhizomes have an orange tinge which is particularly visible after a root is cut. In fact, a Japanese knotweed rhizome will snap easily and when it does the damaged plant tissue will gain an orange colour. Beware, the rhizome is the most invasive element of the whole plant; handle with care! Don’t take root away from it’s original location.
4) Habit: Japanese knotweed is a rhizomatous (produces underground stems) perennial plant which dies back in the winter leaving bamboo like canes which provide a useful means of winter identification. Knotweed forms stands which comprise of basal crowns of plant tissue from which it will regenerate each year. Japanese knotweed grows to 2-3metres and forms large swathes of leafy vegetation in the summer which can easily be mistaken for dogwood or lilac at first glance. In late summer small creamy white flowers appear which hang in clusters making the plant look quite attractive. Young shoots formed in mid to late spring are often red to purple in colour with rolled back leaves. More vigorous spring growth often looks asparagus like in appearance.
5) Winter dead canes: Although the plant dies back in the winter, the stem and leaf material decomposes slowly and because the plant out-competes most other plant species, it is typical to see a swathe of dead canes in the winter months. The presence of this slowly decomposing matter is perfect for trapping litter which in turn has been known to attract rodents.