The Japanese knotweed in summer often catches property owners unaware. The plant grows fast in early spring, thus causing massive property destruction within a short time. This weed can grow from tiny fragments; and looks different each season of the year. 

For example, the Japanese knotweed in summer is more vibrant compared to that in winter.

Identification of Japanese Knotweed in early Summer

Should you worry about Japanese knotweed?

Japanese knotweed may not look like a troublesome plant, because of its beautiful flowers and dark leaves. Unfortunately, the plant has been listed as one of the worst invasive plants in the UK.

It can reduce the value of any property because of its ability to grow through thick cracks and concrete. 

  • Some banks will decline financing properties affected by this weed without any treatment program in place.

The weed is more of a problem in human settlements such as urban areas than it is in natural habitats. The good news is that you can prevent this plant’s destructive nature by learning how to identify it in summer.

Identification of Japanese knotweed in summer

What does Japanese knotweed look like in summer?

It is easier to spot the Japanese knotweed during summer than in spring. During this period, the plant grows at a rapid rate of 10cm a day. Generally, it grows up to 3 meters in height, its green leaves, and flower clusters from the dense foliage.

The flowers emerge as yellow and will gradually turn into white as summer progresses. The leaves will be more noticeable during the end of summer as autumn approaches. They become darker and shovel-shaped.

During this time, the stems become brown- greenish and hollow; they look similar to bamboo.

Tall stems of Japanese knotweed in summer is just one of its characteristics. Growing up to 3m in height
Tall stems of Japanese knotweed in summer are just one of its characteristics. Growing up to 3m in height

Characteristics of a mature Japanese knotweed

Here are features of the Japanese knotweed that can help you identify it regardless of the season:

  1.  Leaves

The leaves of the plant are shovel-shaped with a pointed tip. They form a zig-zag pattern as they grow from the stem. The leaves are often dark green and grow up to 190 mm long.

  •  Flowers

Flowers grow up to 0.5cm wide and 10 cm long. They appear in clusters, as explained above. The flowers together with the leaves create dense foliage; they are creamy-white.

  •  Stems

The Japanese knotweed stems grow up to 3 meters tall. They are often mistaken for bamboo nodes. The stem is hollow inside; it can be easily broken during winter because of its brittleness.

  •  Rhizome

The rhizome system is the Japanese knotweed underground stem. It is fresh and grows up to 7 meters from the plant. Its outer part is dark brown, while the inside is yellow or orange. This root system has the potential to grow up to 3 meters deep. A tiny piece of this root can grow into a new plant.

The root system of the Japanese knotweed through the seasons occupies metres underground
The root system of the Japanese knotweed through the seasons occupies metres underground

What to do if you suspect Japanese knotweed

If you think you have Japanese knotweed growing in your garden or near your property, it is wise to get the help of an expert for inspection. This should be done as soon as possible before the plant becomes uncontrollable.

UK law does not allow you to treat the weed on your property. However, it is vital to note that you could face the law if the plant spreads to the neighbouring land.

Here are some methods of knotweed elimination:

Chemical control: This is the most effective treatment for controlling the weed on small scale land.  The most common herbicide used in chemical treatment is glyphosate. It would be best if you used herbicides towards the end of summer. 

Knotweed removal specialists recommend that the weeds be treated during each season for a minimum of 3 years. You should ensure that you hire an expert to undertake the treatments.

Additionally,  the company you hire should have an insurance backup to protect your interest as a property owner.

Spraying Japanese knotweed in June with herbicides to control its spread
Spraying Japanese knotweed in June with herbicides to control its spread

Mechanical/non-chemical control: Mechanical knotweed control methods are an alternative to chemical treatments. These methods are not highly recommended because of their potential to spread the weed.

Excavation, in conjunction with chemical treatments, maybe the best way to get rid of the plant for good. Mechanical knotweed removal methods require an expert to prevent further contamination.

It is also not advisable to cut the stems or roots into small pieces as these small fragments can grow into a new plant.

The knotweed waste should not be composed but burnt on site. Alternatively, you should ensure that the waste is carried from the site by a licensed waste management company. It should be appropriately sealed and taken to a licenced landfill dumping site.

The Japanese knotweed waste, which includes crown, stem, and root, must be disposed of properly to prevent further spread of the plant.


Japanese knotweed identification is essential in proper planning of how to eliminate the weed. However, one should note that it is not possible to eradicate this weed quickly.

The plant is best sprayed during summer just before winter dormancy. Several treatments are needed in order to completely get rid of the Japanese knotweed.

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 –

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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