What does Japanese knotweed look like?

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What does Japanese knotweed look like?

Many of us involved in construction, utilities and countryside management will have heard of the dreaded Japanese knotweed before, as this infamous weed has earned a feared reputation. Invasive, destructive and fast growing, an outbreak of Japanese knotweed spells bad news for any property due to the extensive damage it leaves behind.

To protect your property and the surrounding area, it’s essential that you can identify Japanese knotweed before it has the chance to spread. But what does Japanese knotweed look like? And how can you get rid of it? The team at Oliver Brown Ltd is here to help with this comprehensive guide on how to handle this threat.

What is Japanese knotweed?

Japanese knotweed is a perennial plant known for its resilience and aggressive spread. As the name suggests, Japanese knotweed is native to Japan, but was brought over to the UK in the early 19th century and intended for use as an ornamental plant before its true nature became apparent.

So what does Japanese knotweed damage do to buildings and infrastructure? With its deep and extensive root system, this invasive weed can push its way through expansion joints in foundations, concrete, brickwork and more, exploiting any areas of weakness that it finds along the way. This can cause cracking and structural damage that can compromise the safety of the entire building; in extreme cases, Japanese knotweed can make a building completely inhabitable. 

How does Japanese knotweed spread?

While Japanese knotweed does produce seeds, these very rarely germinate. Instead, it spreads through its underground rhizomes, which can grow extensively – even up to 10cm a day during the summer months! Even stem fragments as small as 2mm can establish new growth when spread to a new area. Humans can also help to spread Japanese knotweed inadvertently by handling contaminated soil during excavation or construction work.

What does Japanese knotweed look like?

To the untrained eye, Japanese knotweed might look like just another weed. However, Japanese knotweed identification is easier than you’d think and there are a few features that distinguish it from other plants. Here are a few key things you should look out for:

  • In spring: New Japanese knotweed will start to appear in spring, starting as reddish-purple buds and then growing into shoots that resemble asparagus spears.
  • In summer: As the shoots grow taller – usually reaching 2.5m in height – they will develop large, bright green leaves that are shaped like a spade. During late summer, the colour of these leaves will become less vivid and nodes will appear, giving the stem the appearance of bamboo. Clusters of small white flowers will also begin to appear.
  • In autumn: Like other trees and plants, Japanese knotweed will begin to lose its colour in autumn and the leaves and flowers will start to fall off. The shoots will also turn brown and become more rigid and brittle.
  • In winter: Japanese knotweed appears to die during the winter, however, its underground rhizomes are still active and it will start to regrow once the temperature improves.


How to get rid of Japanese knotweed

Without proper intervention, Japanese knotweed can encroach on surrounding properties and obstruct drainage systems and other vital infrastructure. If you have Japanese knotweed growing on your land, it’s your responsibility to ensure it doesn’t spread further than the boundaries of your property; failure to do so could lead to you being prosecuted under Japanese knotweed UK law;

So how do you get rid of Japanese knotweed?

Firstly, you should contact a trusted expert in invasive plant removal, like the team at Oliver Brown Ltd. There are a number of ways we can help:

Herbicides: We can carefully apply the necessary glyphosate-based herbicides to the affected area, spraying it onto the foliage or injecting it into the stem. This method might require several applications to ensure the rhizomes have been fully eradicated, and we can provide you with ongoing support across the seasons.

Excavation: We can physically excavate and remove Japanese knotweed from your property, painstakingly digging out the entire rhizome network to ensure it can’t resprout in the future.

Root barriers: Our highly trained team can install root barriers – a weed-suppressant membrane – at your site to contain a Japanese knotweed infestation and prevent it from growing any further.


If you require Japanese knotweed removal in the UK, get in touch with the experts here at Oliver Brown Ltd. We specialise in invasive plant removal and our experienced team can offer comprehensive treatment plans that promise complete eradication. To find out more or to discuss your needs, give us a call today.


What does Japanese knotweed look like?

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