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What is Japanese knotweed?

You may have heard to stay away from properties which have Japanese knotweed, but why?

It's a quick growing invasive weed which originated in Japan. In the Victorian times, botanists brought it over to the UK because they thought it looked attractive and the stems could be used for fencing.

However, it was soon discovered that the weed is more harmful than beneficial. It destroys surrounding plants, and has huge roots which damage walls and foundations of homes. In less than just 10 weeks it can grow 3 metres tall!

How is Japanese knotweed affecting homes in the UK?

New research has found that a Japanese knotweed infestation decreases a value of a home by 10% or £23,530 on average.

In the UK, there's more than 5% of homes affected by the weed, which means 1.45 million are struggling with the infestation. This adds up and means a total of £34.12 billion is knocked off the value of homes.

Houses of higher value get affected worse, and London homes are seeing an average drop of £47,546. In comparison, South East properties drop by £32,664, East of England by £29,128 and South West by £25,976.

The highest value homes in the UK are in Kensington and Chelsea, London. They are at risk of losing £119,162 off the price of their properties. Westminster and Camden could see a fall of £93,860 and £86,280 respectively. Outside of London, South Bucks experiences the worst drop in price with infestation, at an average of £59,792.

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How can Japanese knotweed be treated?

You may be thinking, why not just remove the weed so the value of homes doesn't drop?

Well, it's not that easy. It also depends on how developed the weed is. If it's not too developed and you can use herbicide to treat it, it'll set you back £2,500. If, however, it needs excavating as the roots have grown deep, it'll cost more like £5,000.

As well as the cost, it can take years to get rid of it. Environet UK, a Japanese knotweed removal specialist, claim that it can take up to 5 years to fully treat, and cost tens of thousands of pound.

What happens if you ignore it?

It's never a good idea to ignore something as harmful as Japanese knotweed. It won't just go away!

Firstly, giving it more time will only allow it to grow further and be more difficult and costly to remove. Plus, it's much harder to sell a house affected by the weed, and you're liable if the seeds spread to neighbouring properties.

If you let the weed take root, it'll grow through cracks in concrete, bricks, asphalt, cavity walls, gutters and drains and force walls to break apart.

It's also harder to get a house mortgage if a property is affected by the weed. house repayments lenders need evidence shown to them of a professional treatment plan and insurance backed guarantee for the work before they offer a loan.

It would be illegal if you had a house infested with the weed and didn't tell any potential buyers. There is a question on the TA6 conveyancing form where you must answer truthfully if your property is affected or not.

When is Japanese knotweed most prolific?

Don't look for the weed during the winter months because it dies back to ground level and is therefore much harder to spot. It starts growing again in March time, and will probably be most apparent around June.

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Mathew McCorry

If you read my property blog now, that'll be the end of it. I will not look for you, I will not pursue you. But if you don't, I will look for you, I will find you and I will make you read it.