Five easy ways to identify Japanese Knotweed

Japanese Knotweed | 09th January 2023

You can identify Japanese knotweed at any time of year provided when you know what to look for, so in this article we explain the common identifiers of Japanese Knotweed.

The five top knotweed identification tips

Below we explain what you should look out for when you are trying to identify Japanese knotweed. However, don’t worry if you are still not sure, you’ll also find a link to our free ‘ID My Weed’ service. You can can use this for Knotweed and the identification of other problematic invasive plants. Simply email us a photo, and your details and we’ll take a look for you.

1. Spade shaped leaf

The spade shaped leaf of Japanese knotweed

Japanese knotweed – Latin name – Fallopia japonica

A Knotweed leaf is sometimes described as heart shaped but the base, where the stem joins the leaf, is very flat and therefore we believe the leaf is best described as spade shaped – like the spade on a playing card. The way the leaves grow are also distinctive, with them appearing on alternate sides of the plant’s stem.

2. Identifying Knotweed’s zigzag stem

Zigzag stem of japanese knotweed

The distinctive zigzag stem of Japanese knotweed.

A common identification characteristic of Japanese knotweed is the growth characteristic of the stems. They appear in an understated zigzag pattern as pictured above. This is more visible on the more mature plants, where the Knotweed protrudes over other plants, standing at a height of between 1.8 and 3 metres tall. Provided the plant is not cut back, these stems will also be visible in the winter months. Surprisingly, the stems can die back into dead hollow canes that still retain the zigzag features of the live plant.

3. Orange tinge to the roots

knotweed root or rhizome

The root or rhizome of Japanese knotweed is orange/yellow in colour when the plant is live.

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 visible root material displays an orange colour. Be aware that the rhizome is the most invasive element of the whole plant, therefore always handle it with care! Or, better still, don’t handle at all and certainly don’t take any part of the root away from its original location.

Need help identifying Japanese knotweed?

Simply email us a photo and we’ll let you know


id my weed

4. Habit provides a big Knotweed identifier

Knotweed is a rhizomatous (produces underground stems) perennial plant which dies back in the winter leaving bamboo-like canes. These tall canes provide a useful means of identifying Japanese knotweed in the winter months. Upon examination, you will see that the plant comprises of a series of plant crowns from which it regenerates each year.

new growth emerging from a knotweed crown

New Japanese knotweed growth emerging from a crown with old canes present.

The Japanese knotweed that grows 1.8-3metres in height forms large swathes of leafy vegetation in the summer. This can easily be mistaken for dogwood or lilac at first glance. However, in late summer you can look out for small creamy white flowers that hang in clusters, making the plant look quite attractive.

At the start of a new knotweed growing season, the young shoots that emerge in mid to late spring are a red to purple in colour with rolled back leaves. The more vigorous spring growth, pictured in the main image of this article, often looks asparagus-like in appearance.

Japanese knotweed clusters of creamy white flowers

The creamy white flowers of Japanese knotweed typically emerge towards the end of summer.

5. Even dead winter canes help identifying Japanese knotweed

Knotweed canes in the winter

Japanese knotweed canes become brown and brittle in the winter months.

Although the plant dies back in the winter months, the stem and leaf material decomposes slowly, and because the plant out-competes most other plant species, it is fairly typical to see a swathe of dead canes. The presence of this slowly decomposing matter is perfect for trapping litter, this in turn can attract rodents to the location if not cleared.

Contact PBA Solutions

For more information on how PBA Solutions can help you, or your community, in identifying and removing Japanese knotweed and other invasive weeds, email or call us on 0203 174 2187.


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