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

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Japanese knotweed is a fast-growing and strong clump-forming perennial that grows to a depth of 3m with a radius of 7m. Although originally introduced to Britain as an ornamental garden plant, it is an invasive non-native species

It is estimated that 1.45 million homes are affected by this weed in the UK.

But, what can you do about it? We take a closer look at why it is often seen as a nuisance.

Japanese knotweed history

Selling your home in spring? Consider the history of certain plants in your garden, like the one introduced to the UK by the Victorians. Initially admired for its red shoots and heart-shaped green leaves, it was a popular choice for herbaceous borders during spring and summer. This plant grows rapidly, up to 2 cm a day, but appears to die in winter. However, the Victorians soon discovered its destructive nature and turned against this once-favored plant.

What does Japanese knotweed look like?

Many people are unsure of what the plant looks like, making identifying it 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 similar plants 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 Japenese knotweed do?

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!

What impact does it have?

The presence of this non-native weed can feel like a negative impact on homeowners.

However, The Royal Institution of Chartered Surveyors (RICS) has published a new Guidance Note for surveyors that has abolished the ‘seven-metre rule’ valuers use when determining whether Japanese knotweed poses a threat to a property.

This industry body has published a 36-page guidance note that “reflects an improved understanding” of Japanese Knotweed. Which can sometimes make a mortgage application or selling a property more difficult.

The guidance states “Research has demonstrated, and it is now generally accepted, that Japanese knotweed poses little or no risk of structural damage to robust buildings with substantial foundations such as dwellings, as opposed to less sturdy structures with shallow foundations, such as conservatories, garages or boundary walls,” 

So the extent of the damage it can cause is down to how well your property is built.

How do deal with Japanese knotweed?

Wondering how to get rid of Japanese knotweed? It’s tough, but there are some methods you can try to remove it.

Summer and early autumn are the most common times for the plant to grow. However, it’s worth being aware of the potential threat it could pose all year round.

Understanding what the Japanese knotweed lookalikes are will help you spot any potential problems in advance.

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 has their advantages and disadvantages.

Japanese knotweed eradication can be expensive and can take up to three years to have any effect.

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

  • Try to stop it spreading – spraying or injecting the stems with approved herbicides (chemicals) can be an effective treatment to stop knotweeds spreading. You must do this every year until there is no evidence of regrowth.
  • Removal: 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

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.

What to do if you find Japanese knotweed

If you find it growing in or near your property, and have it removed, you may be required 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 the 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 will need to disclose the presence of this invasive plant. However, while you may view it as an opportunity to negotiate a house price, the maintenance costs involved and the hassle of removing it might far outweigh any money you’d save on the property.

Before committing to buy a house with Japanese knotweed be 100% sure of its impact on the property, as it can be tough to remove. So, if a seller discloses its presence take a good hard look at things before you commit.

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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Last Updated: January 8th, 2024