Japanese Knotweed: What does it look like and how much can it damage your house price?

·4-min read
It is illegal to plant Japanese Knotweed in the wild. (Getty)

Japanese Knotweed is a plant many homeowners fear - but what should you do if it makes its way onto your property?

It's one of the world's most notoriously difficult to eradicate weeds that can kill gardens and knock a sizable amount off a person's home.

Recently four homeowners won tens of thousands of pounds from Network Rail after the weed, which was widely used to support tracks on embankments, spread onto their property and grew as high as 2.5m.

What is Japanese Knotweed?

Japanese Knotweed, as you might expect, originated from East Asia but is now prevalent across much of the world.

Japanes Knotweed can grow several metres tall. (Getty)
Japanes Knotweed can grow several metres tall. (Getty)

It 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 and deep roots which can damage concrete foundations and other structures.

The weed can survive in temperatures as low as -35C grow up to 7m high and put its roots 3m deep.

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 it grows.

While some reports say the plant is poisonous most experts agree it is not - the 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 it 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)

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 much can it affect house prices?

According to Environet, an invasive plant specialist, the presence of Japanese Knotweed on a property can lower its price by as much as 10%.

What's even worse is most lenders will refuse to offer a mortgage on the property if the weed is present and will often require it to be professionally removed before considering changing their mind.

A poll by YouGov found half of all buyers would walk away from a property if they knew was affected by Japanese Knotweed.

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Most of those who would still consider buying the house said they would ask for a considerable discount.

Owners are required to disclose the presence of Japanese Knotweed on their property when they are looking to sell.

How do you get rid of it?

As previously mentioned, the biggest problem with Japanese Knotweed is how difficult it is to remove.

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 often requiring a digger.

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

Shoots of Japanese Knotweed, Polygonum cuspidatum, Fallopia japonica. Green natural background, close-up, top view
The presence of Japanese Knotweed can knock up to 10% off the price of a home. (Getty)

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

While many herbicides can be used a very 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, if the weed has been growing for years and been allowed to spread its root as far as possible it will be considerably harder to remove.

Where is it most commonly found in the UK?

A survey by Environet found Japanese Knotweed was prevalent in many areas of the UK.

It was least present in Northern Ireland, but Wales, Scotland and England all had numerous hotspots.

The worst place in all of the UK was around St Helens and the wider Merseyside area.

Other places with significant Japanese Knotweed problems were London, south Wales, north west Wales, Norwich, Glasgow and a stretch of land between Nottinghamshire, Derbyshire and South Yorkshire.

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