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How to Identify Japanese Knotweed

The most easily identifiable characteristic of Japanese knotweed is the shape of its leaves – which are heart or shovel shaped. Be cautious about identifying Japanese knotweed based on its looks alone, as these can change depending on the time of the year.
When identifying Japanese knotweed, look out for the following:

  • Heart or shovel shaped leaves
  • Creamy white flowers might bud in late summer
  • Zig-zagging growth patterns

Early-Stage Identification Japanese Knotweed

The best time of the year to identify Japanese knotweed is in the middle of summer. During early Spring, purple shoots will appear above the ground, just as buds’ forms and bloom outward as ‘spears’. As these grow – reaching up to 2cm daily – these start to form bamboo-like pillars.

In early summer, when it’s the best time to identify Japanese knotweed, the stems will have matured and developed a purple pattern. At this stage, they grow into a zig-zag.

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Download Our Knotweed Identification Guide

As the identification process can be challenging, depending on the time of the year and the conditions of the environment, we’ve developed a guide to help you understand the timeline of growth and change that occurs in this plant throughout the seasons.

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Identification of Japanese Knotweed Throughout the Seasons

Japanese knotweed is a perennial plant, meaning its appearance changes with the seasons. It starts with small fleshy roots in the spring, growing up to 10cm per day and over 3 metres high in the spring and summer, before dying back to brittle, leafless canes in the winter where it is less identifiable.
Knotweed can spread from very small sections of root at an alarming rate and can cause problems to foundations and drainage of a property if left untreated.

Summer

The combination of sheer height and density of Japanese knotweed in the summer makes the plant easily identifiable. At an average of between 2-3 metres high in full bloom, the spade shaped leaves and spiky stems with creamy white flowers make the plant appear attractive. However, the exponential growth above ground masks the speedy way in which the underground rhizomes are expanding.

Knotweed is a good source of nectar and may attract bees and other pollinating insects and full bloom begins around late August.

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Autumn

The appearance of Japanese knotweed in autumn will have very similar traits as in late August, as the flowers will be in full bloom until October. Towards the end of October and through to November, the leaves will start to wilt and turn yellow and the stems will become dark brown in colour and start to become dormant.

Winter

The leaves have fallen and the dark brown canes will appear to be decomposing and may collapse and intertwine.  New seasons shoots may already begin to appear under the dense brittle canes. Whilst in winter, knotweed remains dormant above ground, below ground the rhizomes are still present and may continue to grow.

It is highly important to make sure you have an expert carry out Japanese knotweed identification to help to determine whether you have an infestation. Failure to do so can lead to the plant quickly spreading across your premises and neighbouring properties, leading to damage. Get in touch with the experts today to find out how we can create a treatment and removal plan.

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See More Japanese Knotweed Pictures

Don’t rely on guesswork, especially when it comes to such a destructive and costly plant. When attempting to identify Japanese knotweed, it’s helpful to look at pictures – many of which highlight just how invasive this plant can be.

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Professional Japanese Knotweed Identification

Japanese Knotweed Specialists are the leading invasive species identification and removal professionals in the UK, capable of sourcing, treating, and disposing of various aggressive plants.

If you suspect growth of Japanese knotweed on your property, you have a legal obligation to act on it. Contact a specialist today to ensure peace of mind – we’ll help you identify and treat any infestations.

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