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What is Japanese Knotweed and What Can You Do About It?

Phi Spencer

By Phil Spencer

Did you know that a plant could wipe significant value off your property? Even if it’s not actually on your land?

Japanese knotweed is that plant.

In fact, in 2017, a couple sued the individual they bought their home from, 15 years prior, because she had failed to disclose knowledge of Japanese knotweed near the property and the extent of the problem.

But, what is Japanese knotweed and what can you do about it? We take a closer look at this plant and why it’s such a nuisance.

What is Japanese knotweed?

Japanese knotweed is an incredibly resilient plant, usually found on wasteland sites, but sometimes creeping its way into gardens.

Growing to a depth of 3m with a radius of 7m, it can cause thousands of pounds worth of damage to buildings and sites.

Japanese knotweed history

The plant was introduced into the UK by the Victorians who thought it would look good in their gardens.

With its red shoots and heart shaped green leaves adorning any herbaceous border in the spring and summer, it’s easy to see why this plant was once considered attractive. It grows up to 2 cm a day, before appearing to die in the winter.

However, the Victorians quickly turned against their new favourite plant when they realised quite how destructive it was. But, by then it was too late, the damage was done.

What does Japanese knotweed look like?

Many people are unsure of what the plant looks like, making identifying Japanese knotweed difficult.

Above ground, it looks fairly nondescript. It’s green with heart-shaped leaves and bamboo-like stems, sometimes blooming white spiky flowers.

Due to this unassuming appearance, some plants confused with Japanese knotweed include bamboo and field bindweed. As a result, it can go easily undetected.

However, looks can be deceiving! Below ground is another matter altogether.

What does Japanese knotweed do?

Whilst Japanese knotweed isn’t poisonous, it’s extremely harmful.

Its roots, which can extend down to 7ft render, are virtually impossible to remove yourself, without the use of extreme chemicals.

If left unchecked, these roots can exploit weaknesses in any building, causing significant structural damage to walls, drains, floors and hard surfaces. It can also grow up to 10cm a day, easily creating new areas of infestation!

This means that this plant not only affects the health of your garden, but your entire property also!

Japanese knotweed house damage

As recent reports have indicated, the presence of this destructive non-native weed, can knock thousands of pounds off the value of your property, in some cases, up to 10%.

Property Wire reported that a landmark ruling has allowed UK homeowners to sue their neighbours if Japanese knotweed ends up on their land. This means that the responsibility of dealing with the problem falls with the owner of the property which it originates from.

How do you get rid of Japanese knotweed?

Wondering how to get rid of Japanese knotweed? It's tough, but there are some methods you can try to remove this troublesome plant. Be persistent!

The key is to deal with the problem immediately, to prevent it spreading and becoming near-impossible to remove. Summer and early autumn are the most common times for the plant to grow, however it’s worth being aware of the threat all year round.

Understanding what the Japanese knotweed lookalikes are will help you spot the problem before it gets out of control.

If you already have Japanese knotweed growing on or near your property, there are a few courses of action you can take, either chemical or non-chemical. Each have their advantages and disadvantages. 

Unfortunately, Japanese knotweed eradication is expensive and can take up to three years to have any effect.

But, here’s what to do if you find Japanese knotweed:

  • The best way to get rid of Japanese knotweed is to spray the plant with approved chemicals (herbicides) - glyphosate-based weed killer
  •  Afterwards, dig it out, let it dry, and burn it. This involves digging down to the roots and disposing of the plant appropriately - you can’t dispose of it with normal household waste as that can cause it to spread. Never put it in green waste bins without killing it first
  • Alternatively, some homeowners choose to use the eco-friendly MeshTech method

But, it's important to note that trying to tackle the problem yourself can make the situation worse or could affect guarantees you might require in the future, so it's important from the outset to get the correct advice with a coordinated approach with neighbouring landowners.

Treatment should be repeated annually until there is no evidence of regrowth.


What to do if you find Japanese knotweed

It's worth noting that Japanese knotweed is not typically covered under most general insurance policies. If you find it growing in or near your property, and have it removed, you will most likely have to take out a special knotweed indemnity policy to prevent potential future attacks of the plant and to mitigate against all damage it can do.

These special indemnity policies provide cover for cost of treatment, any damage caused by the plant, third party legal fees (should the plant have spread onto neighbouring properties), and the resultant devaluation of any property found with Japanese knotweed growing in or near the grounds.

If you have any doubt about Japanese knotweed, speak to the Environmental Agency, or contact specialist removal companies.

Should I buy a house with Japanese knotweed?

So, what does this have to do with those buying a home?

Sellers are required to disclose information concerning this harmful plant. However, while you may view it as an opportunity to negotiate a house price, the maintenance costs involved and hassle of removing it might far outweigh any money you’d save on the property.

Buying a house with Japanese knotweed is an enormous commitment, as, clearly, it’s extremely tough to remove. So, if a seller discloses knowledge of the hazard, think twice about buying, even if it’s your dream home.

Research is absolutely key! Want to learn more about your area? With a property report, you can find out everything you need to know about a specific area, from local schools to who the neighbours are. Get your full report here!

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