28% growth in UK Japanese knotweed cases in just 5 years
Study reveals findings from 49 UK environmental authorities – including worst affected areas – showing 28% growth in Japanese knotweed cases.
Analysis by Horticulture.co.uk has found that confirmed cases of Japanese Knotweed have grown by 28% in the UK in just five years.
The study collated National Biodiversity Network figures from 49 local authorities in Britain – including the Environment Agency, National Trust, Botanical Society of Britain & Ireland, Natural England and others.
The invasive plant species was originally imported into Britain from Japan back in the nineteenth century, when engineers thought it would stabilise and beautify railway embankments. It has since spread like wildfire across the UK, with more than 29,000 confirmed cases growing in number each year.
The underground roots of the plant are known to be extremely difficult to eradicate completely, with most affected property owners having to undergo protracted treatment plans at significant costs.
Its presence can also lead to difficulty when selling your property.
According to our YouGov survey of 907 UK homeowners:
- Four in five would walk away from buying a property affected by knotweed
- Of those who would consider purchasing a property with a known knotweed invasion, almost two-thirds of buyers would expect at least a 5 – 10% discount on the expected sale price
- One in twelve had never even heard of Japanese Knotweed
Perhaps the most worrying finding is that nearly half (47%) didn’t recognise a knotweed plant from our line-up of plant images.
Analysis of the 29,536 confirmed cases in the UK show the regions with the largest growth in live cases over the last 5 years:
| County | Total Confirmed Live Cases | 5 Year Change |
| South Yorkshire | 1,111 | +77.19% |
| Hampshire | 123 | +73.24% |
| West Sussex | 155 | +72.22% |
| Kent | 217 | +64.39% |
| Powys | 923 | +61.93% |
| North Yorkshire | 215 | +58.09% |
| Cardiff | 280 | +53.01% |
| West Yorkshire | 1,762 | +52.82% |
| Surrey | 200 | +49.25% |
| Shropshire | 146 | +47.47% |
| National Average | 29,536 | +27.91% |
Horticulture.co.uk have launched an interactive map where residents can pinpoint confirmed cases of Japanese Knotweed in their local area.
The page also provides further guidance on how to identify and report the plant in the UK.
Dean Wilson at Horticulture.co.uk comments:
“When instructing a surveyor for your new home purchase, always ask them to look for Japanese Knotweed and other invasive plants.
“This is especially important if the property borders an old or existing railway line, or is close to a river, canal or stream – where the plant is known to spread via small fragments of root that work their way downstream.”
According to the data, there are a further 19,702 unconfirmed cases of Japanese knotweed, with thousands more in the UK likely to remain unreported.
A national eradication programme was proposed in 2015, but this was rejected by the Government at the time due to its “prohibitively expensive” cost – estimated to be in the region of £1.5 Billion.
Kindly shared by Horticulture.co.uk
Main photo courtesy of Pixabay
