Japanese Knotweed: find out if your property is in a high risk area and how to manage the invasive species

Environet has launched a UK interactive map to show where Japanese Knotweed is most prevalent.

As summer arrives in the UK many people will be opting to spend more time in their garden, and what better way to enjoy the UK heatwave than planting new flowers. However, those looking to do so should be aware that Japanese Knotweed has been found in many properties.

Japanese Knotweed is an invasive species that gardeners should be highly aware of due to the damage it can cause.

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Environet has  launched their own interactive heatmap designed to inform homeowners and homebuyers of the local presence of knotweed and the potential risk to their property, the data is generated from over 50,000 known infestations, with new sightings added daily.

Last year, a man in London discovered the invasive species in his newly purchased home and successfully sued the previous owner of his house after discovering a large amount of Japanese knotweed in his garden, resulting in a £200,000 court bill. Making a seller aware of the presence of Japanese knotweed has been legally required since 2013.

According to the Royal Horticultural Society, the seller is required to state whether Japanese knotweed is present on their property through a TA6 form - the property information form used for conveyancing. So, what is Japanese Knotweed? Here’s everything you need to know about managing invasive species.

What is Japanese Knotweed?

Beginning to grow in April-May, Japanese knotweed is a massive root system that utilises weaknesses in building foundations and connecting drainage systems, and causes gradual damage, resulting in a faulty structure over an extended period of time.

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It could cost the average UK property up to £40,000 for professional Japanese knotweed removal and a further £9,500 for structural damage repairs depending on the impact it has had over time amounting to nearly £50k in fees.

How to find out if your area is high risk

The interactive heatmap to find out whether your area is high-risk for Japanese Knotweed can be found on the Environet UK website. All you need is your postcode and the database will tell you whether or not you should be concerned about the invasive species in your area.

Scientists at the University of Leeds have discovered a possible breakthrough in controlling Japanese knotweedScientists at the University of Leeds have discovered a possible breakthrough in controlling Japanese knotweed
Scientists at the University of Leeds have discovered a possible breakthrough in controlling Japanese knotweed

How to stop knotweed spreading

According to the Government website, homeowners should not treat knotweed on their own unless they have the appropriate skills or they can find companies that specialise in treating knotweed.

Spraying or injecting the stems with chemicals can be an effective treatment to stop knotweeds spreading but only approved herbicides can be used. Respraying is also needed as it usually takes at least three years to treat Japanese knotweed.

When using chemicals, you may need to:

  • make sure anyone spraying holds a certificate of competence for herbicide use or works under direct supervision of a certificate holder
  • carry out a Control of Substances Hazardous to Health assessment
  • get permission from Natural England if the area is protected, for example sites of special scientific interest
  • get permission from the Environment Agency if the plants are near water

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