Map shows worst areas for Japanese knotweed

An infestation may need specialist removal.

People looking to move house in the near future are being warned to watch for the signs of Japanese Knotweed.

The invasive plant, which spreads incredibly quickly, can damage homes and can impact both the property’s value and the buyer’s ability to get a mortgage.

Leading invasive plant removal specialists Environet reckon about 5% of homes across the UK are affected by Japanese Knotweed, whether directly or due to the spread of the weed from a neighbouring property.

The presence of the weed can drop house prices by up to 10% in severe cases – and the company has produced a heatmap showing where the invasive plant is most pervasive.

The map has been created based on details of more than 57,000 Japanese Knotweed infestations, with new sightings added regularly – but how can potential homeowners spot the dangerous plant? Metro.co.uk has everything you need to know.

What does Japanese Knotweed look like?

Japanese Knotweed looks similar to bamboo and grows to around 6.5ft to 10ft in height.

The shoots are red in colour in the spring before turning green in the summer.

The leaves, which are shield or heart shaped, appear in spring and grow along the length of the shoots.

Bunches of creamy white flowers grow amongst the leaves from late summer.

They then die back in winter, leaving the brown, dead looking canes above ground – but the plant spreads through its underground root system, which are dark brown on the outside and orange inside.

The roots burrow deeply and break easily, making them difficult to remove completely.

What are the risks of Japanese Knotweed?

Japanese Knotweed grows incredibly quickly, at a rate of up to 4 inches a day in the summer.

Its roots can reach as far as 10ft below ground, which can damage the concrete foundations of buildings.

It’s not illegal to have Japanese Knotweed on your own land, but if it causes a nuisance or spreads to the wild or other land, you could be prosecuted and fined up to £2,500.

House sellers are legally required to declare the presence of Knotweed on their property, and you still have to declare that it has previously been present on your land, even if it’s been removed.

How do you get rid of Japanese Knotweed?

If you find Japanese Knotweed in your garden it’s recommended to contact a specialist removal company.

They can use a glyphosate-based herbicide, which kills the plant when injected into it at the correct time of year.

However it could take a few years of repeated application to completely eradicate the plant.

Many removal companies recommend continuing with the glyphosate treatment over a number of years.

Where are the worst Japanese Knotweed hotspots in the UK?

Our map, based on Environet’s data, suggests that there are a number of hotspots for Japanese Knotweed across the UK.

London is a major hotspot, as are Bristol, the southern and eastern Welsh coasts, spots in central England including Derby and Nottingham, western England including Liverpool and Greater Manchester, Glasgow, Edinburgh, Aberdeen and Fort William in Scotland, and the Isle of Man.

That isn’t an exhaustive list, and the map suggests Japanese Knotweed has a presence across most of the UK, including even remote areas like the Shetland Islands and Scottish Highlands.

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