Japanese knotweed: What is it, what does it look like, and how to get rid of it

·3-min read
Japanese knotweed: What is it, what does it look like, and how to get rid of it

A homeowner who spent £1.3 million on a London house has won £50,000 after a surveyor failed to spot Japanese knotweed in the garden of the property.

Paul Ryb bought the two-storey, brown-brick property in Highgate, north London in part because he liked its big garden, reports the Mirror.

The former investment banker, who has trouble with his eyesight, recruited the help of a surveyor to look over the property. In a report, the surveyor said the property was in “excellent condition” and had “very few defects”.

But he did not notice the clumps of Japanese knotweed in the garden.

After Mr Ryb had paid his deposit and moved in, the gardener spotted the knotweed, refused to even touch it and left the property.

The invasive plant could have consumed Ryb’s garden over time, so spent more than £10,000 having the area cleared.

Mr Ryb sued the surveyor and was awarded £50,000 in damages.

The plant, known as Japanese knotweed, is known to cause property damage, potentially depreciating the value of the home and even stopping other plants from growing in the garden.

What is Japanese knotweed?

Japanese knotweed is a type of invasive plant species notorious for its propensity to spread, causing damage to building structures and costing up to tens of thousands of pounds.

“In winter, the plant dies back to ground level but, by early summer, the bamboo-like stems emerge from rhizomes deep underground to shoot to more than 2.1m (7ft), suppressing all other plant growth,” explains the Royal Horticultural Society (RHS).

The weeds are almost impossible to remove by hand or eradicate with chemicals.

What damage does Japanese knotweed cause?

The weeds are known to block pipework and going on to clog sumps and drainage pits.

Water pipes and cabling are other underground infrastructures susceptible to damage in its wake.

Japanese knotweed is also known to have major environmental and legal implications.

In fact, specialists from across the UK have documented a huge portfolio, including evidence of major damage which has been caused by Japanese knotweed over the past 25 years.

What kills Japanese knotweed?

A weed killer, which is glyphosate-based, is considered one of the better options for getting rid of the weed.

Glyphosate is a systemic herbicide that takes several applications over up to four seasons to completely eradicate it.

Spraying or injecting the stems with other chemicals which are approved herbicides may also help but, again, the substance needs to be resprayed, taking up to three years to fully treat and kill the weed.

What does Japanese knotweed look like?

According to Warner Goodman, signs you may have Japanese knotweed include:

  • Zig zag stems

  • Lush green colour leaves

  • Shield shaped leaves with a flat base

  • Bamboo style stems

  • Red tinged shoots

  • Found in dense clumps

  • In July it will sprout clusters of white flowers

  • Between September and November it will leave brown stems once the leaves have died back.

If you are concerned you may be at risk of Japanese knotweed you can use the Heatmap which shows sightings of the weed in your area highlighting the level of risk using a scale of yellow to red colouring.