Japanese knotweed identification has remained a significant challenge in the UK.  With more property owners asking this very question, ” How do I know if I have Japanese Knotweed on my property?”.

It is not easy to identify Japanese knotweed without mistaking it for several other plants that are nowhere near as much an issue.

There are several species of plants that can be easily mistaken for this weed.  The plant has the potential to cause substantial destruction when ignored and open you up to legal issues.

If you are looking into buying a property, you must know how to determine if it is affected by the Japanese knotweed. The plant is invasive, and it can be quite costly to get rid of it. In most cases, you will require an expert company to plan for effective treatment.

Read on to learn how to know whether you have the Japanese knotweed on your property.

Japanese Knotweed leaf and stem anatomy
Japanese Knotweed leaf and stem anatomy

What does Japanese knotweed look like?

How do I know I have Japanese knotweed, What does it look like? Proper identification of Japanese knotweed needs accurate information and a keen eye. This weed has a good number of unique characteristics, but it can also be mistaken for several other plants.

Proper inspection of each part of the plant you suspect to be Japanese knotweed will let you know if you have the weed on your property or not.


The weed has rhizomes that are referred to as underground stems. The rhizomes system is fresh and breaks when bent. It is dark brown on the outside and orange inside.

The roots can grow up to 3 meters deep and 7 meters horizontally. It is this system that spreads the knotweed.


The knotweed stems have been likened to those of bamboo. They have nodes and purple speckles. The leaves grow from these nodes in a zigzag pattern. The stem is hollow on the inside when mature. It only becomes brittle during winter.


The leaves of this knotweed are shaped like a shovel with a pointed tip. They grow on the stem from the nodes in a zigzag pattern. The leaves grow up to 250mm long and broaden during summer.


Japanese knotweed flowers appear in clusters. The flowers are creamy-white and appear at the end of summer and early autumn. These clusters are about 0.5cm wide; they create dense foliage with the leaves.

The flowers of the Japanese knotweed bloom and spread during late summer
The flowers of the Japanese knotweed bloom and spread during late summer

Japanese knotweed through the seasons

Characteristics in spring

The weed grows fast in spring.  It is easier to notice new shoots that are either purple or pink. The leaves will be dark green and rolled up during this time.

The knotweed canes measure at least 3 meters and 12 feet high. The crown also forms during this time of the year. These buds are round in shape at the lower part of the old stems; they measure about 3 cm wide. The buds are usually pink or red. The stems grow each year from these crown buds.

Characteristics in summer

The knotweed flourishes in summer. The leaves are incredibly green and shovel-shaped during this period. Towards the end of summer, clusters of flowers form, and white flowers appear in early autumn. The stems are mature and hollow.

Characteristics in autumn

During autumn, the dense covering of the leaves remains.  You will notice some yellowing on the leaves as October approaches. At this time, the plant will measure between 2-3 meters tall. The stems will become brown as winter approaches.

Characteristics in winter

The knotweed stems start to die during early winter.  The leaves will also turn yellow or brown before they fall off completely. The plant will then become dormant for some months. The canes will even break and fall on each other, and decomposition will kick in as soon as possible. 

Is Japanese knotweed a shrub?

This weed is mistaken for a shrub due to its large foliage.  The knotweed is perennial with a hollow stem, which is not a characteristic of a bush. Shrubs have woody stems. The Japanese knotweed stem easily breaks when bent while those of shrubs can be easily stripped away.

Other ways to tell you to have Japanese knotweed

The knotweed infestation comes in several sizes, making it difficult to spot them. The plant is likely to be lost in an ingrown garden more so during winter when the weed becomes dormant. Here are some other risks factors that are linked to Japanese knotweed infestation:

  •  Knotweeds grow in vast public lands such as parks, untilled land, or car parks.
  •  The weed can be found in properties near large industrial buildings, stores, or workshops.
  • Properties near water bodies such as rivers, ponds, or lakes.
Identifying whether you have Japanese knotweed or not amongst so many other weeds in a garden

What is the best time to spot Japanese knotweed?

This plant changes through the seasons, as shown above. This constant transition makes its identification challenging. In most cases, several plants can be mistaken for Japanese knotweed. 

It is easier to spot the Japanese knotweed during summer. The stems are usually hollow with purple speckles and measure about 3 meters in height. You will notice that the leaves alternate on the opposite side of the stem.

If you are still unable to determine if you have the Japanese knotweed, take photos that you can send to an expert to help you identify it. Several companies are specialists in Japanese knotweed identification; you can easily find one near your location.

How do I know if I have Japanese knotweed is becoming easier to spot due to its dominance over other plant species?
How do I know if I have Japanese knotweed is becoming easier to spot due to its dominance over other plant species?

What do I do if I find Japanese knotweed at my property?

Individual eradication attempts are not effective since this weed is invasive and can be dormant for a very long time before growing again. It is not advisable to cut the leaves or stems of the plant since it will flourish within a short period. Several weed killers are sold in stores.

Unfortunately, not all weed herbicides are effective in eradicating this plant. The most effective way to eliminate this weed for good is to hire a specialist company. These are trained experts that know what works and what doesn’t. 

Want to know more?

Knotweed Removal aims to provide the most up-to-date information, help and advice for YOU to make informed decisions. If you are unsure or uncertain about how to proceed, please reach out to us and we will gladly come back and advise you as best we can.

Governmental advice can be found here and the UK law covering the removal of Japanese Knotweed as stated under the Wildlife and Countryside Act 1981 can be found here.

the best means to contact us is via our email – hello@knotweedremoval.tips

Do not forget we have a library of blogs covering many areas relevant to Japanese Knotweed, our free downloadable How-to Guides and Product Reviews on the latest methods being employed to eradicate or remove Japanese Knotweed.

Knotweed Removal, UK

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