What is Japanese knotweed? How to identify and remove the invasive plant

It is illegal to plant Japanese knotweed in the wild. (Getty) (Christopher Kimmel via Getty Images)

Japanese knotweed has brought misery to millions of homeowners across the UK and has been the centre of many a court dispute.

The invasive plant is notoriously difficult to get rid of, and in some cases can cause damage to buildings and completely overrun gardens.

It is illegal to sell a property without disclosing the presence of Japanese knotweed, as discovered by chartered accountant Jeremy Henderson, who was recently in court over the sale of his London home.

He claimed he “reasonably believed” there was no knotweed in his three-bedroom house in Raynes Park when he sold, but a judge said not enough checks had been made, and ordered him to pay £32,000 in damages.

Here, Yahoo News UK explains how to tell if you have Japanese knotweed and what to do if you discover it.

What is Japanese knotweed?

Japanes Knotweed can grow several metres tall. (Getty)
Japanese knotweed can grow several metres tall. (Getty) (Andrew Francis Wallace via Getty Images)

Japanese knotweed originated from East Asia but is now prevalent across much of the world.

The plant has been classified as a pest and invasive species in many nations and is incredibly hard to get rid of.

It is extremely resilient and grows wide with deep roots that can damage concrete foundations and other structures.

The weed can survive in temperatures as low as -35C, grow up to 7 metres high, and puts its roots down around 3 metres deep.

Read more: These are the areas in South East London being overrun by Japanese Knotweed

It retreats underground in winter, but can grow extraordinarily quickly in summer.

Japanese knotweed has been compared to bamboo – although they aren't related – because of the speed at which it grows.

While some reports say the plant is poisonous, most experts agree it is not. Its threat comes from its ability to wreck all nearby plants and structures.

It is such a problem in the UK it is illegal to plant it in the wild and it can only be disposed of at special landfills.

What does Japanese knotweed look like?

Japanese Knotweed has been compared to bamboo for the speed it grows at and it's thick branches. (Getty)
Japanese knotweed has been compared to bamboo for the speed it grows at and it's thick branches. (Getty) (SoopySue via Getty Images)

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Japanese knotweed looks like a lot of green leaf plants but can be identified by its thick bamboo-like stems.

It grows into a very dense thick bush with the vast majority of its leaves on the top exposing the bamboo-like branches below.

One of the best ways to identify Japanese knotweed is to ask yourself if you'd seen that plant before, as a whole bush can grow in a matter of weeks.

How to get rid of Japanese knotweed

The most common route is to go via a specialist, and even then it will take three to five summers to get rid of it properly when using the most common methods.

The quickest method is to simply dig into the ground and pull out all of the roots, but the weed is so extensive it can mean a large area of land will need to be excavated, which can often require a digger.

The other commonly used method is to spray the weed with herbicides twice a year.

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Invasive plant control of Japanese Knotweed, Fallopia japonica, near St Keverne, Cornwall, England, UK. (Photo by:Geography Photos/Universal Images Group via Getty Images)
The most common way to tackle Japanese knotweed is to go to a specialist, but even then it can take some time. (Getty Images) (Geography Photos via Getty Images)

It can take anywhere between three to 10 years to thoroughly poison the plant enough for its roots become so weak they are unable to properly regenerate in the spring.

While many herbicides can be used, a particularly powerful one is needed to do the job properly, and these are often not easy to find in conventional shops.

The most important factor is the age of the plant, and whether the weed has been allowed to grow and spread its roots as far as possible – which will make it considerably harder to remove.