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Japanese Knotweed: How to spot it and what to do if you find it

Japanese Knotweed: How to spot it and what to do if you find it

Fewer than one in five property owners can identify Japanese Knotweed, a survey by Environet found.

Indeed, some of you may even be wondering what it is.

Put simply, Japanese Knotweed is a plant that can cause incredible damage to your property and is very hard to stop in its tracks.

Japanese Knotweed in property: What you need to know

Japanese Knotweed, as you might have guessed from the name, is not a native plant to the UK.

It was brought in from Japan, Korea and China in the 19th century and has spread rapidly across the UK since then.

It grows most aggressively around wet areas such as canals and lakes, but has also taken hold around railway embankment – and people’s gardens.

What does Japanese Knotweed look like?

The fact that many homeowners are unable to identify Japanese Knotweed gives it an even better chance of spreading.

Japanese Knotweed buds sprout in spring and are red in colour, before red shoots appear and grow into hollow stems which are often mistaken for bamboo.

The stems are green with purple flecks and Japanese Knotweed leaves turn from a yellow/brown colour in spring to rich green in summer.

The shovel-shaped leaves can grow around 14cm in length and are followed by small white flowers in the autumn months.


How common is Japanese Knotweed?

It’s estimated that between 1% and 5% of homes in the UK are affected by Japanese Knotweed, which given there are an estimated 25 million homes in the country, is a considerable problem.

What damage does Japanese Knotweed cause?

The main issue with Japanese Knotweed is the structural damage it causes to property.

It can work through cavity walls, drains and through cracks in concrete and asphalt, meaning the external structure of your home could be severely affected if you have an infestation.

Why does it spread so quickly?

Japanese Knotweed can grow up to 10cm a day in summer and the rate it spreads at is often boosted by homeowners attempting to remove the plant themselves.

It’s underground network of stems mean it is extremely difficult to remove completely, even by professionals, and a new plant can grow from a piece of stem no longer than a fingernail.

It’s also extremely resilient, meaning a dried-up, seemingly dead piece of weed can regrow if it comes into contact with soil or water.

Japanese Knotweed removal – what not to do

Many homeowners, who often just think Japanese Knotweed is a fast-growing plant, will simply trim it back or take a garden strimmer to it.

Once the cut stems come into contact with soil or water, they can form a new growth within 10 days.

Others attempt to remove it with weed killer or chemical sprays and once it appears dead, believe the problem has gone away.

This is often not the case as Japanese Knotweed underground stems can sit dormant for up to 20 years and grow once again.

How to kill Japanese Knotweed

Essentially, the only way to remove Japanese Knotweed from your property for good is to use a professional.

But beware: It’s not a quick process and can be costly.

Consistent use of weed killer is the method most commonly used for removing Japanese Knotweed, but often treatment will need to be carried out over a number of years.

Another option is to dig up the plant and its underground stems, but it must then be disposed of according to Environment Agency guidelines.

Severe infestations of Japanese Knotweed can see treatment costs spiral, so it pays to seek advice from the Environment Agency if you believe you may have the plant on your property.

Fines for Japanese Knotweed

It’s not an offence to have Japanese Knotweed growing on your property.

But you could be facing a heavy fine or even a prison sentence if you cause the spread of the plant in the wild by dumping contaminated soil or remnants of the plant.

You could also face legal action from neighbours if you don’t take steps to control the plant and it infiltrates their properties.

Can I still sell my home if I have Japanese Knotweed?

You can, but an untreated infestation could lower your property’s value by up to 20%, it’s estimated.

Buyers are also entitled to know if a property is affected by Japanese Knotweed and failing to disclose information like this could see you facing legal action from the buyer.

Who to contact if you suspect Japanese Knotweed

A host of companies offer professional surveys to establish Japanese Knotweed growth and from that, a treatment plan can be established.

Before agreeing to a treatment plan, be sure that the specialist offers a guarantee of at least five years should the plant return and require further treatment.