The worst exposed Japanese knotweed hotspots in the UK

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:


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Dangerous’ garden plants which can decrease property value by up to 15% – how to identify

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.

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Free Japanese Knotweed Survey – discover the facts about your knotweed

Mrs Walsh wrote: The Japanese Knotweed that grew in my garden was quite large, and the roots were so big and thick I couldn’t cut them with any normal tools. This plant has taken over my garden and I am worried it will damage my foundation if I don’t get rid of it soon. Luckily, there are professionals out there who know how to treat it safely and effectively – but they come at a price! I didn’t want to spend money on expensive treatment though, so I took advantage of the Free Japanese Knotweed Survey available across England & Wales.

What is Japanese Knotweed?

Japanese Knotweed is a non-native invasive weed that was brought into the UK in the 1900’s and today is estimated to affect 950,000 residential properties around the UK. It can cause devaluation of your property, be expensive to treat and/or remove, and can cause untold damage to foundations of your property, affect water and sewerage pipes, and stop you re-mortgaging your property or selling it.

What problems can it cause?

Japanese knotweed is a species of plant that can cause huge problems to buildings, roads and other structures. In fact, if left unchecked, it can cause serious structural damage. Luckily Japanese knotweed is easy to treat and we have a 10-year insurance backed guarantee. If you find it in your garden or anywhere else on your property, call us immediately for a free survey.

How do I treat it?

Only an expert should treat the Knotweed which typically is a 3-year treatment plan within a 10-year Insurance Backed Guarantee

How much does it cost to treat it?

Costs vary depending on the site, amount of Knotweed present, age, type of Knotweed and many other factors. Our FREE and WITHOUT OBLIGATION Knotweed Survey gives you all the facts with an inclusive quotation for treatment and an Insurance Backed Guarantee.

Why are we offering this survey?

Japanese Knotweed Agency operate the UK’s Japanese Knotweed National Register and work with many partners across the UK in the fight to eradicate Knotweed and help people protect their property.

Is there a Guarantee?

If you take up our partners treatment plan after your survey and quotation, once the first treatment has taken place, you are covered by the inclusive 10-year Insurance Backed Guarantee.

How do I take part in the survey?

To request your FREE and WOTHOUT OBLIGATION On-Site Survey, just request a Survey form to your email here:

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Knotweed Survey – Sign up for the free knotweed survey and learn more about this invasive weed.

You have probably seen knotweed in your neighbourhood, and you may have even wondered what it was. Knotweed is an invasive weed that reproduces like crazy and can wreak havoc on your property value, as well as any structures it comes into contact with. Luckily, now you can have a FREE AND WITHOUT ANY OBLIGATION survey about the knotweed on your property and learn more about the invasive species. Click here to sign up for the free knotweed survey today!

What is Japanese Knotweed?

Knotweed is ranked towards the top end of the World’s Most Invasive plant species and should not be underestimated on what adverse effects it can have on your property.

Japanese Knotweed spreads very fast and grows at a rapid pace throughout the summer months in the UK and can exploit all types of land and terrain and even grow through tarmac, brickwork, walls, drains, sewers, cavity walls and literally anywhere it can exploit to will do so.

Knotweed is said to affect 950,000 houses across the UK and can significantly reduce the value of your property, cost thousands of pounds to treat, can stop house sales dead in their tracks, can leave you open to litigation if it spreads from your land on to another person’s land and cost you tens of thousands of pounds.

The good news is that if it is coming from another person’s land such as railway, council land, commercial land and so on, you can typically recover all of the costs of treatment and insurance plus recover a significant cash sum to cover any devaluation of the property value.

How Can I Tell If I Have Knotweed?

You can visit our Seasonal Gallery on the below link and make yourself aware of how Kno0tweed looks throughout the seasons.

How Much Is My Property Worth with And Without Knotweed?

In the very best circumstances devaluation can be 5% of the property price, so £150,000 property value will have a minimum loss of £7,500 – plus the cost of a treatment plan and 10-year Insurance Backed Guarantee.

Where Knotweed is identified to be a fair infestation, and may be evidence of it growing in drains, sewers, close to the property or inside the property, the valuation will decrease significantly. Some severely affected properties have seen a 100% devaluation because of the extreme growth and other factors such as access to be able to treat and so on.

The Knotweed will only get worse, so you need to act fast if you think Japanese knotweed is on your land. In most cases you should be able to recover all costs and get compensation.

How Do I Remove the Weed from My Property?

A specialist treatment firm will typically attend at least once every 3 months and treat the weeds by injecting the stems of every plant again and again, and this will go on for at least 3 years, followed by a 2 year observation by the homeowner.

Once treatment starts, you should then be covered with a 10-year Insurance Backed Guarantee, so if it does come back after the 3-year treatment, your insurance will cover any additional treatments required.

What Should I Do Next?


Your survey will highlight the locations of the crowns of Knotweed and where it is coming from and spreading to; it’s direction of growth and travel, and serious issues, age, and lots more, to give you 100% expert, factual information inside an extensive written report bespoke for your property, and will include a full quote for treatment and an Insurance Backed Guarantee.

How do I get a FREE Survey?

It’s simple and straight forward, just click the link below, enter your details and then check your email for the enhanced form.

We check the completed form first to ensure it is Knotweed that is present so we don’t waste your time or ours. Once we identify the Knotweed, we will arrange a surveyor to attend, and you’ll then get a full copy of the report and then decide how best to proceed.

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Japanese Knotweed and its impact on property values

We all know that Japanese knotweed can be pretty destructive, especially if it’s allowed to grow out of control and invade the landscaping of neighbouring properties. But how much does this invasive species affect property values in general? And why does it have such an impact on home valuations? Let’s take a look at how Japanese knotweed devalues property and how to deal with it in your own backyard.

What is Japanese Knotweed?

Japanese knotweed is a type of weed that can have negative effects on land, property and surrounding areas. The weed spreads quickly and can even damage properties in which it grows. It’s important to understand how Japanese knotweed will devalue your home before you decide to purchase a new home with it on.

Japanese knotweed (Reynoutria japonica) has been dubbed the worst weed in the UK by the Royal Horticultural Society, owing to its tenacity and the difficulty of eradicating it once it takes hold in a garden or property. Not only does it pose an aesthetic problem, but it’s also responsible for devaluation of properties when real estate prices are assessed to factor in its presence as either a potential risk or actual threat to nearby homes and buildings. This article explores how Japanese knotweed causes property devaluation and what can be done about it…

Signs of Japanese knotweed

Japanese Knotweed is quite distinctive and easily recognised once you’ve seen it once, you can pretty much identify it at all times. Knotweed has a distinctive rounded heart shaped leaf and thick stems that typically grow 6 inches per day in the UK throughout the summer.

You can check our Gallery through the seasons to see what the invasive weed looks like all year round:

Why it’s important to get rid of it

Although knotweed can’t cause any direct harm to your health, you may want to keep it away from your home if you care about how much your house is worth. According to a study published in 2013 by Nottingham Trent University, knotweed infestations can reduce a property’s value by as much as 15 percent. Depending on the size of the infestation and its proximity to buildings, it could render a property unsellable.

Knotweed will only keep growing and spreading so to ignore it could be extremely detrimental to your property and your pocket. If you allow Knotweed to spread from your land to a neighbour’s land or into the wild, it is a criminal offence and can carry a heavy fine and you could also end up with a claim against you which could run into tens of thousands.

How to get rid of it

Because Japanese knotweed can be difficult to control, chemical treatment will be necessary. Several specialist herbicides are available that work well with Japanese knotweed, such as glyphosate (Roundup), triclopyr (Weedol), imazapyr (Pursuit) and aminopyralid (Milestone). These are systemic herbicides, meaning they need to be taken up through plant roots or stems to have an effect; cutting them down will not help. A specialist treatment firm knows how to do this properly and it usually takes a visit every 3 months for 3 years to get a full treatment delivered.

An Actionable to Do List

First thing is getting your Knotweed formally identified by the Japanese Knotweed Agency, and where positive, request a FREE Onsite Survey and you’ll get a full report to show the locations of the crowns, age, route of growth, lots more information and a quote for a treatment plan that comes with an Insurance Backed Guarantee.

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How to Claim for Japanese Knotweed Trespass

If you’ve found Japanese knotweed growing on your property and don’t want it there, you may need to take legal action against the owner of the land where it has grown. This guide will teach you how to claim Japanese knotweed as trespass, so you can get your property back to full health and full value.

What is knotweed?

Knotweed or Japanese Knotweed is an invasive plant species which was brought to the UK in the early 1900’s as a decorative plant, unbeknown that it spreads like wildfire and can cause damage to property and amenities. Knotweed ryzomes (root system) and root growth can grow vigorous and can even grow through tarmac, concrete, water pipes, sewer pipes and can get into property foundations and cause havoc.

Knotweed can grow up to 8 inches a day in the summer and grow as tall as 12 feet high. The stems grow thick like bamboo and small stems grow from the main stems and grow a thick bush of leaves and even flowers through August and September.

What does trespassing mean?

If something from another person or property comes on to your property or land without your knowledge or consent, that is considered to be trespass. The fact that Knotweed has come from another parties land on to yours, and causes devaluation and other problems and can cost you money to put right, this is a recoverable trespass issue.

What are the options to resolve this issue?

If Knotweed is coming from a neighbour, the best approach in our opinion is to speak with your neighbour and try and get an amicable solution between you both. A survey and treatment plan with an Insurance Backed Guarantee will ultimately help both of you. If the Knotweed can be seen to be coming from your neighbour to your land quite obviously, your neighbour may agree to pick up all the costs. This is something hopefully as neighbours you can sort out.

If your neighbour doesn’t listen to your friendly request, you should put it in writing and allow them a small amount of time to get some resolve. Knotweed will only grow and spread if it is left and that will be worse for everyone.

If the Knotweed is coming from a commercial neighbour like the railway or council land or a commercial enterprise, report it formally so you have a record. Many times we see that although reported, the commercial entity doesn’t take it seriously enough or carry out proper treatment, then the problem again will only worsen.

The fact that Knotweed will not go away on its own, and a typical treatment plan with an Insurance Backed Guarantee can cost a few thousand pounds, you need to ask yourself should you pay for it if the neighbour is at fault? Then you need to think about any damage to your property and any devaluation because of the presence of Knotweed, and ask if you are happy with that or want to take action to protect your own asset.

If you decide to make a claim against the neighbour land owner, you can typically do this on a No Win No Fee. You should be able to recover the full cost of a treatment plan and force your neighbour to treat the Knotweed on their land to ensure it doesn’t come back again. You should also be able to claim the cost of the Insurance Backed Guarantee, and cash compensation for the devaluation of your property because of the presence of Knotweed. This may be an average of 10% of your property value, so a £200K property should start a claim for £20,000 plus treatment plus guarantee and maybe some additional compensation for inconvenience.

Which option should I choose?

The choices are really down to you. As your house and property is usually your biggest asset, it is important that you take this seriously and probably that you seek expert legal support to ensure you are fully protected.

How much will it cost me?

Japanese Knotweed Agency offer a FREE – WITHOUT OBLIGATION On-site Survey anywhere in England & Wales, which will give you all of the information you need to make a decisive way forward. The Survey Report will give you information on where the Knotweed has travelled from, its age, all identified crowns and growth areas, any potential damage caused by the Knotweed, and will also report on up to 58 other invasive weeds if any of those are present.

Your Survey Report will also come with a full quotation for treatment and a 10-year Insurance Backed Guarantee that if any Knotweed comes back after the treatment and within 10-years, it will get treated for free under the guarantee.

The Survey and report are 100% FREE and WITHOUT OBLIGATION

With that information you can then decide how to proceed and whether to move forwards with any legal claim. The options are then yours with detailed information at hand.

Request your FREE Onsite Survey here:

When should I claim Japanese knotweed as trespass?

As above, if you are friends with your neighbour and the Knotweed is coming from their land to yours, it may be best to speak together and try come up with an agreement.

If the neighbour doesn’t take notice or take action, the Knotweed will only get worse week by week, so you shouldn’t wait too long before taking action, whichever route you choose.

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Understand the laws regarding Japanese Knotweed

According to some reports, homeowners are not aware of their legal responsibility to stop Japanese Knotweed spreading. Only 36% of them know they can be sued and only 18% are aware that they could face criminal prosecution. Japanese knotweed should not be ignored. This page contains information that will help you understand the laws regarding Japanese knotweed.

Japanese Knotweed can grow in the garden of a landowner’s property. He should take every precaution to prevent the invasive weed spreading to neighbouring properties. If this fails, he could be held liable for any damage that was caused by the encroachment. If the knotweed is growing on your property, the landowner could be held responsible.

Give Notice to Your Neighbour

If you want to sue your neighbour, you should give the person or organization responsible for the adjacent land the chance to address the nuisance (knotweed) unless it has been there for quite some time and must be obvious that they are already aware. You should notify your neighbours as soon as possible. Also, make sure you specify what actions you want the landowner to take.

You should ask your neighbour to treat knotweed on their property as well as on theirs. Ideally, the remedy they choose should also include a guarantee. You should also include a description of the possible consequences for them if they ignore the notice. If the knotweed is from commercial land or infrastructure like Council or Network Rail, they are more than likely already aware.

Unreasonable Conduct

A Community Protection Notice (CPN), which can be used under the Act, can be used to order someone to stop or control the growth of Japanese knotweed and other plants that could cause serious problems for communities. The conduct of an individual or body must have a negative effect on the quality or life of others in the area. Section 57 of the Act defines conduct as “a failure to act”. CPNs could be used to force someone to stop or control the growth of Japanese knotweed, or other plants that can cause serious harm to communities.

Fixed Penalty Notice

If an individual or organization isn’t controlling Japanese knotweed, or any other invasive plant, and it could reasonably be expected that they would, the CPN could then be used. A mandatory written warning must be served before the CPN can be used to force them to cease their anti-social behaviour. A community protection notice violation without reasonable excuse would be considered a crime and subject to a fixed penalty. A summary conviction would result in a fine of not more than PS2,500 for an individual. A fine of not more than PS20,000 is possible for an organisation such as a company.

Paramount Knotweed Management Plan

Knotweed is not a reason to deny a mortgage application. Instead, it should be considered on a case-by-case basis. A suitable Knotweed Management Plan must be presented. It can be shocking to discover that your property has knotweed or that your property is infested. However, there are ways to control the infestation. The Knotweed Management Plan is the key.

Legal Rights Against Misrepresentation

Japanese knotweed is a serious problem in the country. The seller must disclose this information to you when buying a house. If the Japanese knotweed is present in a property you’ve purchased, you may sue the seller.

Property value loss

Knotweed infestation can cause property value loss. If a property is found to be infested with Japanese knotweed or Japanese knotweed within 7 metres of the property, it will make it extremely difficult to obtain a mortgage.

A property that is affected by Japanese knotweed loses its value, regardless of whether it is within their boundaries or within 7 metres. This is known as diminution of value. It may be possible to include a claim of diminution in any settlement if you succeed in bringing a Nuisance Claim on a defendant.

Professional Negligence

If you paid for a professional inspection of your property, and the surveyor failed to notice the Japanese knotweed, then you could file a claim for professional negligence against the surveyor. You can file a claim if you can prove that the surveyor should’ve noticed the Japanese knotweed.

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Japanese Knotweed and its detrimental affect on the property industry

The property industry is being hit with problems caused by Japanese knotweed. In just 10 weeks, it can grow 10 cm per day and can reach a height of 3-4 meters. It is illegal for someone to cause or allow the invasive plant spread onto another property.

A new study has shown that the UK has seen an astonishing 28% increase in Japanese knotweed cases in the last five years.

The results of analysing 29,536 confirmed cases of Japanese knotweed in the UK from 49 environmental organizations including National England, Environment Agency and National Trust were reached. The Japanese Knotweed Agency has also started a National Register for England and Wales.

It is extremely difficult to remove the underground roots of this plant. The nationwide treatment of the invasive plant may take up to three decades.

Ask your surveyor to check for Japanese knotweed or other invasive plants when you hire them as a consultant for your new home purchase.

This is particularly important if your property borders an existing or old railway line or is near a river, canal, or stream, Council land or commercial property.

Horticulture conducted a YouGov survey previously to learn more about the plant’s impact on the property market.

According to the YouGov survey, 4/5 of UK homeowners said they wouldn’t buy a house with Japanese knotweed. Just under half of those who said they would still buy the house agreed to lower the price at least 10%.

Many homeowners are not familiar with the plant, according to the survey. The reason is that only half of respondents could identify Japanese knotweed using a selection of photographs.

Questions remain about the government’s response to Japanese knotweed.

A national eradication program was proposed in 2015, but it was rejected by the government due to the staggering £1.5 billion cost.

Due to the current year’s weather, Japanese Knotweed is fast-growing and an invasive plant. This causes homeowners more problems than ever.

Its wet and frosty spring was followed by sunshine and dry weather earlier in the year. Experts are anticipating a rise in Japanese Knotweed incidence, which is already flourishing and growing rapidly.

Buyers and sellers must realise that there is a real possibility of an infestation or evidence of it in their property. This could cause a property to be unable to sell or stop selling.

Japanese Knotweed is a legal requirement for home sellers. The TA6 Property Information Form is used to notify buyers about any negative aspects affecting their home. It also includes a question pertaining Japanese Knotweed.

It is difficult to get a mortgage for a property that has Japanese Knotweed or had it in the past. Many home insurance policies won’t cover Japanese Knotweed. They also won’t cover damage to neighbouring properties or the cost of removing or eliminating the plant.

Japanese Knotweed is classified as a controlled waste under the Environmental Protection Act 1990. It can grow up to 20cm per day. If it is not controlled, its roots can reach deep into foundations and cause damage to walls and drainage systems.

It must be removed and disposed of by an expert. The cost will vary depending on how large the infestation is.

For homeowners, the only way to protect against any damage or remediation caused by Japanese Knotweed in their home is to purchase a Japanese Knotweed-specific insurance policy.

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How Did Japanese Knotweed Get Here?

Japanese Knotweed is a contentious plant that can depreciate the value of a property and cause conflict between neighbour’s. The invasive plant is known for spreading quickly and for monopolising gardens. Knotweed grows in large patches that can quickly push out any other competing plant life. Thankfully, Japanese Knotweed is easy to identify, so homeowners can waste no time in getting a treatment plan in place to get rid of the plant.

Although there is plenty of discussion regarding how Japanese Knotweed spreads, and what to do if you’ve bought a property with Knotweed, how this plant first got to the UK is not usually discussed. Japanese Knotweed’s history is an interesting one and can help give insight into why it has flourished so well in the UK and what lessons can be learned when dealing with invasive plants in the future.

Where is Japanese Knotweed originally from?

Japanese Knotweed is originally from Japan and is also native to China and Korea. The plant is one of many species of plants that have been discovered to be growing on the side of volcanoes. In its native land, Japanese Knotweed can reproduce naturally and also benefits from a prodigious underground system of rhizomes. In its native environment, Knotweed is kept in check by natural predators in the form of fungi and insects, not to mention other plants and an environment that can be much more hostile than the United Kingdom.

The plant was originally discovered by Dutch naturalist Maarten Houttuyn in the 18th-Century, he named it Reynoutria japonica, a name which it still goes by today. Unfortunately, the records of this original discovery were lost for some time, so when more European botanists started exploring Japan some 150 years later, the plant was rediscovered and given a new name by a Bavarian botanist, Phillip von Siebold. Siebold and his partner Zuccarini, named the plant Polygonum cuspidatum. It wasn’t until the turn of the 20th century that a Japanese botanist by the name of Makino, discovered that Houttuyn and Siebold’s plant were one and the same.

Who brought Japanese Knotweed to the UK?

Philip von Siebold brought Japanese Knotweed to the UK in 1850, unaware of the impact that it would go on to have on the environment. At the time, botany and the cultivation of plants was a popular interest of the upper classes. Botanist like Siebold would be able to fund their research trips by sending their discoveries back to nurseries on the European continent, where they would then be cultivated and sold onto commercial nurseries or botanical gardens around the world.

Why was Japanese Knotweed imported to the UK?

Japanese Knotweed was imported to the UK for commercial sale and botanical cultivation. Over the time that he spent in Japan, Siebold collected and recorded over 1,000 different plants, often choosing to plant them in the garden behind his research base on Dejima, an artificial island near Nagasaki. Periodically, Siebold would box up a number of samples and send them back to his home in the Netherland. From their new home in Leiden, these plants would be carefully grown and the packaged up for botanical gardens in Belgium and Britain, with an unmarked box containing Japanese Knotweed arriving at London’s Kew Gardens in 1850.

Kew Gardens often relied on these boxes of new plants to keep their own collections diverse and interesting for visitors. After discovering how quickly the plant could grow in Britain, the horticulturists there recognised Japanese Knotweed as a plant that could be easily cultivated and sold on to budding gardeners. Soon the plant was being distributed to garden nurseries around the country and then shared in cuttings by enthusiastic gardeners. In addition to being intentionally spread by people, the plant also began to spread by its own means, populating river banks and finding new routes to the rest of the country along roads and newly built railway lines.

Where does Japanese Knotweed grow in UK?

Japanese Knotweed now grows in almost every area of the UK. The plant was given free rein to spread throughout the country for over a hundred years before being recognised as invasive by the government. By the time Japanese Knotweed was identified as an invasive threat in 1981, it had already been spread by gardeners, dug up and transported by urban development projects and even used to stabilise soil on the sides of railway lines.

The plant is frequently found growing alongside public watercourses such as canals, as well as near railway lines, motorways and public footpaths. Japanese Knotweed thrives in most conditions in the UK and is often found growing on land that has been abandoned or left unattended. For this reason, large infestations can often be discovered in overgrown back gardens, or on abandoned industrial sites.

How common is Japanese Knotweed in the UK?

Japanese Knotweed is a very common sight in the UK. Since the government has made the spread of Japanese Knotweed a more pressing concern, efforts have been made to track where it has been growing throughout the country. Using these statistics, it’s been possible to recognise the areas of the country that have been most affected by Japanese Knotweed. Bolton, Bristol, Conway, Rotherham and Nottingham are areas in the UK that have been affected the most, however exact numbers are difficult to assess

What do I do if I find Japanese Knotweed?

If you find Japanese Knotweed it’s important to ascertain where the plant has come from and to what extent the plant affects your property. You may want to consider contacting a Japanese Knotweed specialist to make a positive identification before you move forward with talking to any neighbour’s who might also have the plant on their land. Ignoring the infestation is not advised, as the plant can quickly multiply, leading to a larger problem to deal with and potentially more costs, if you find that it’s not possible to claim compensation for the cost of treatment.


If you think you’ve found Japanese Knotweed and would like some advice on what to do next, then you can contact us by calling freephone 03335 777 888 or send us a message using the contact form on this page.

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How Japanese Knotweed Affects House Insurance: Are You Covered?

Japanese Knotweed can have a negative impact on the value of your property, not to mention causing conflict between neighbour’s and causing stress in your day-to-day life. Discovering a Japanese Knotweed infestation can also lead to some very expensive costs, which many might wish to alleviate by relying on their home insurance. Unfortunately, making a claim on your home insurance after discovering Japanese Knotweed is not always straightforward, or even possible, in some cases.

Does house insurance cover Japanese Knotweed?

Most house insurance policies will not cover losses incurred as a result of Japanese Knotweed. However, there are some exceptions to this rule, such as if the plant has caused subsidence, or if it has spread from a neighbouring property. Having Japanese Knotweed on your land also might prompt other questions, such as how it could affect your premiums and if your insurance might cover the legal costs of a Japanese Knotweed claim made against you.

Will my insurance provider pay for treatment of Japanese Knotweed?

Home insurance providers will not pay for treatment of Japanese Knotweed. If you have discovered the plant on your land and can prove that it has either entered from a neighbouring property, or the seller has lied about the Japanese Knotweed, then you may be able to claim compensation to cover the cost of damages.

Am I covered for damage caused by Japanese Knotweed?

Standard house insurance policies do not typically cover the costs related to repairing the damages caused by Japanese Knotweed growing on your land. However, in the case that the Japanese Knotweed has caused structural damage to your home, like subsidence, you may be able to claim for damages. Although, successful claims are only likely to be made when you can prove that you have taken reasonable steps to eradicate the Japanese Knotweed before the subsidence took place.

This is a good example of how important it is to not delay dealing with a Japanese Knotweed infestation, doing so can result in serious repercussions such as the above, as well as the potential legal implications of allowing the plant to spread to a neighbouring property.

Will my insurance cover Japanese Knotweed from a neighbouring property?

Depending on your policy, your insurance may cover the cost of repairing damage caused by Japanese Knotweed entering from a neighbouring property. In this circumstance, your insurers may seek to pursue your neighbour’s for the costs related to the damage to the property.

Will my insurance cover legal expenses if my neighbour claims for Japanese Knotweed damages?

Your insurance policy might cover the cost of legal expenses in the event that your neighbour attempts to claim for compensation for damages caused by Japanese Knotweed entering your land.

It is against the law to allow Japanese Knotweed to spread from your land into a neighbouring property, regardless of if it’s publicly or privately owned. If your neighbour can prove that you have allowed the plant to spread into their land then you could be found liable for the loss of value of the property, as well as any treatment costs that the infestation might have incurred.

In most cases, you are able to add-on legal expenses insurance on to your standard home insurance policy. You may wish to assess the fine print in your current policy if you’re worried that you might not be covered for this eventuality.

Do I need to inform my insurance provider that I have Japanese Knotweed?

You do not need to inform your insurance provider about the Japanese Knotweed on your land. In the event that you find Japanese Knotweed on your property, you should do as much as you can to prevent it further spreading and causing damage to your property. If you fail to do this, your insurance provider may decline a future claim for damage caused by subsidence, on the grounds that you have acted negligently in not treating the problem sooner. In the eventuality that you are directly asked about the presence of Japanese Knotweed on your property by your insurance provider, you must be honest with them.

Can I get house insurance if I have Japanese Knotweed?

You can still get house insurance if you have Japanese Knotweed on your land. As standard house insurance policies do not tend to cover the costs of removing Japanese Knotweed or the damages caused by the plant to the property insurers are not likely to take this into account. However, in the case that you are directly asked about having Japanese Knotweed, it’s recommended to answer honestly and openly.

Will having Japanese Knotweed affect my house insurance premiums?

Having Japanese Knotweed shouldn’t affect your home insurance premium. Most standard house insurance policies will not cover the removal of Japanese Knotweed, or repairs to anything damaged by it. As such, your discovery of the plant, whether or not it has originated on your land, should not affect your premiums.

However, in the case that you plan on claiming for damages related to subsidence caused by Japanese Knotweed, you will likely find that your premium will increase. Don’t forget that, in the event that you do make a successful claim, you will also have to pay the excess laid out in your policy. Claiming for subsidence cover can also negatively impact your ability to get insurance cover for subsidence in the future, as your home will have been flagged as high-risk by the insurance companies.

What insurance do I need to cover me against Japanese Knotweed?

Since 2015, it has been possible to buy specific Japanese Knotweed insurance which covers the cost of removing the plant, and the potential costs related to claims against you, as a result of the Knotweed spreading to a neighbouring property.

A Japanese Knotweed indemnity insurance policy will cover the costs of treating and removing the infestation, in addition to preventative insurance-backed measures to stop the plant from returning. The policy should also cover the cost of a Japanese Knotweed survey, as well as any reparation costs in relation to damages to the property and legal expenses paid for as a result of claims made against you. These policies were created with the intention of easing the conveyancing process, in cases where homes have been affected by the plant.

Japanese Knotweed insurance policies are usually for 10 years, with the limit of indemnity being based on your property’s market value, offering valuable protection to both you and your mortgage lender. It should be noted that these Japanese Knotweed indemnity policies are only available for residential properties where the presence of the plant is not known, or if treatment has taken place to the satisfaction of the mortgage lender.

Too little, too late?

Unfortunately, Japanese Knotweed indemnity policies, such as the above, have not been advertised to their full extent, so for many, the discovery of them will be a case of too little, too late. If you’ve found Japanese Knotweed on your land, and have found that your insurance does not cover the costs of repairing damages or removal, then you may be able to seek compensation against the seller of the property or even the persons or organisations who have allowed the plant to spread to your land.


Get in touch with us by sending a message using the contact form, or calling us freephone 03335 777 888

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