Is the invasive species in your back garden? Japanese Knotweed Agency map the areas in the UK most at risk from Japanese knotweed

Japanese knotweed is a lot more common in the UK than you might think – and it costs the UK economy over £40million a year.

The plant, native to Asia, was initially brought to the UK in 1850 in a box delivered to Kew Gardens and was much sought-after for its pretty flowers. However, its fast-growing roots led to a wild proliferation – and now the plant can be found all over the UK.

Bolton has been revealed as the Japanese Knotweed capital of the UK in 2022, with the North-West of England making up three of the top four most badly affected locations.

Bristol comes in second and St Helens in third, while Wales is another particularly hard-hit region, with three places in the top 10.

So, what are key attributes of Japanese Knotweed and where are the most badly affected areas in the UK?

Japanese knotweed can grow several inches a day

It hibernates through winter and reawakens in the spring and spreads rapidly, with its root network expanding at an alarming rate. By midsummer, it can grow by several inches a day, and can be identified by its creamy white flowers which bloom around August.

Each root can grow to be three metres deep and several metres horizontally, often piercing through foundations, driveways and walls and causing extensive damage.

In 2021, Dr Ross Cuthbert, of Queen’s University Belfast, led a project to analyse the economic impact of all the UK’s invasive species, and found that since 1975, the plant has cost the UK economy at least £41million a year.
The majority of [Japanese knotweed’s] economic impact is in house devaluation from when you have knotweed on the property, and also the cost of removing an infestation,

Japanese Knotweed Agency have released their National Register in 2021 and seen over 35,000 records submitted by surveyors, homeowners, members of the public and people who enjoy the countryside. That shows how many infestations have been registered in particular areas which you can search by the first part of your postcode to see what has been reported near you.

Bolton has 684 infestations within a 2.5-mile radius of the town centre, whereas Bristol has 475 and St Helens 441.

Streatham, in south-west London, is the only location in the top 10 in the London area, and came in at ninth with 300 logged infestations.

Rapid urbanisation and a defeatist attitude to the species were to blame for its increased prevalence in the North-West and Wales.
The plant had become such a scourge in these areas that many believed it was too prevalent to begin to combat.

Urbanisation helps spread Japanese knotweed

Increases in urbanisation have also seen more soil being moved from one site to another, taking the plant — which can regrow from a lone, finger-sized piece of root — to new areas which it then takes over.

I think the reason why we see it far more in cities is because there has been more and more human movement of soil. A lot of that goes back to the Second World War when there were huge amounts of materials being buried, moved around, bombed etc and obviously there is still a massive amount of the weed in London.

There is also a lot of it in Wales and the reason for this is that for many, many years, the attitude was, ‘well, there’s so much around that there’s nothing we can do about it’.

Also, because land values are quite low in the area there’s no financial incentive to fully excavate it as opposed to just using herbicides to keep it under control.
If there was a million-pound house in London we would likely say that the value of the property justifies getting rid of the infestation properly, which means digging it up. So that might be a ten grand fee for a £1,000,000 house. But if you did the same in, say, Swansea, that house might be worth £100,000 so the treatment starts to look quite expensive.

So, in these sorts of properties, you would just go for a herbicide treatment and control it that way. But controlling is not killing it and it is most certainly not killing it all which is needed to prevent it spreading.”

According to research, approximately one in 20 homes are currently affected by knotweed, either directly or indirectly.

By publishing the 2022 British Japanese knotweed hotspots we hope to raise awareness and encourage people in the area to be vigilant for signs of knotweed as the growing season takes off, so they can act quickly if needed.

Anyone living near or moving to one of these hotspots would be wise to check their garden carefully, enter their postcode into Exposed to find out how many known occurrences are nearby and if in doubt, seek expert help.

Japanese Knotweed Agency offer a free onsite survey that provides a substantial report highlighting where any crowns of the weed are, its age and route of growth etc, and also checks for up to 58 other invasive plant species found in the UK. There’s a full quotation included by one of their registered specialist firms that comes with an Insurance Backed Guarantee, and the Agency can also advise if you are able to make a claim against a third party for the recovery costs of the treatment and Insurance Backed Guarantee, and also claim compensation for devaluation, with a typical claim value well over £10,000

If you are a homeowner and have Japanese Knotweed on your property, get your free Knotweed survey today:

FREE JAPANESE KNOTWEED SURVEY – CLICK HERE

WITH summer on its way, experts are urging homeowners to look in their gardens to see if they have certain plants which can “damage” property and “devalue” it.

Buying and selling property is often a stressful time, which can be made even more hard when invasive plants are found in the garden. To help homeowners identify plants before purchasing a new home, or to solve current issues, Japanese Knotweed Agency have unveiled the most “common” plants which can devalue property by as much as 15 percent.

Japanese knotweed is an invasive plant which is identified by its creamy white flowers, bamboo-like stems and shaped leaves. It is the most invasive weed in the UK, infamous for its devastating ability to cause costly damage. Its roots can reach down to 10 metres underground, making it extremely difficult to eradicate, and the spread of the weed could damage pipework, pines and weaken building foundations.

Due to this, Knotweed is listed as a defect to the property by RICS Homebuyer Reports, with the potential to reduce the price of property by as much as 15 percent.

Alan Hoey, Managing Director at the Japanese Knotweed Agency said “It is really important to check yourself or get a professional in to check and take immediate and thorough eradication actions before it gets too late if you find you are affected by Japanese Knotweed.

“We highly recommend you seek professional help when removing Knotweed as they re-establish easily from even the smallest remains of the root system.

If your property is affected by Knotweed and you are the owner, Japanese Knotweed Agency offer a free onsite survey and full report, along with a quotation for a herbicide treatment plan and 10-year insurance backed guarantee by a professional and qualified partner firm.

Request your FREE Japanese Knotweed Survey and Report

Similar to Japanese knotweed, giant hogweed is invasive and can spread very fast. It is often spotted in July and can be identified by green stems with purple shoots and white flowers. The expert said: “Widespread really across the UK, especially found around rivers and ponds, its sap is phototoxic and can cause severe skin burns or scars under sunlight.

“Though not causing direct harm to the property, buyers may still refuse to pay a higher price if present because of its high cost of removal, up to £15,000.”

According to the experts, Ivy is also “dangerous to your house”, with a strong wall-climbing ability. It can cause wall cracks, damage the mortar and bring dampness into the home. “Unlike giant hogweed, English ivy could be removed with bare hands by peeling them carefully off the wall. “It is also possible to kill them by cutting their roots and letting them dry out.

“However, not all wall-climbing plants are harmful, such as Boston ivy, so we recommend consulting a professional before mistakenly cutting some beautiful and safe plants from your wall.”

While most trees cause no harm, the experts said large ones such as poplar, willow and oak can be dangerous if grown close to property.

Poplar trees have fast-growing root systems which can spread out to 40 metres and take up 1000 litres of water and nutrients from the soil. “They could live around 50 years and are harder to remove when their roots grow thicker and bigger as time progresses. Their age, soil type, location, depth all matter when deciding whether your tree is a problem. If grown too close to your property, they could lead to further risks or cracks in foundations, subsidence and other structural defects, potentially costing you £5,000 to £25,000 to repair.”

Another invasive plant which can spread seeds metres away is the Himalayan balsam.

It was brought to the UK in 1839. It grows up to two to three metres tall and has pink flowers in summer and early autumn. It can kill off other plants and reduce biodiversity by stealing lights, nutrients and water.

It does not have physical danger to humans but its significant ecological impact on nature and associated laws are not favoured by buyers.

So, it is recommended to keep this plant controlled or eradicated, and make sure it does not spread to your neighbours’ home as it can be illegal.