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There are a lot of things to compete with when it comes to buying a new property. The housing market is a heavily saturated arena. Even after they’ve got an offer accepted, buyers still have hurdles to jump and obstacles to conquer. There are the estate agent fees, the cost of homebuyer reports and structural surveys and conveyancing outlays – and that’s before we’ve even taken into account the risks of gazumping.

However, while these things are part and parcel of scaling the property ladder, few people expect their plans to be destroyed by a plant.

Japanese Knotweed in the UK

This exotic-sounding plant is an unknown quantity to many people. But, for those of you who have come into contact with it, you’ll know that it’s an absolute nightmare. A plant capable of destroying a building and resisting all attempts at repulsion, the discovery of Japanese knotweed on a building can lead to serious complications for buyers, sellers and owners alike.

But what is Japanese knotweed? Originally introduced to the UK as an ornamental plant, in the past 200 years it has since grown exponentially to become the UK’s most invasive plant species, costing the country around £166 million annually in damages and control measures. Despite its natural habitat being on the side of volcanoes (which, on reflection, shows just how tough this plant is) Japanese knotweed has spread like a virus into populated areas, growing by up to 10 cm a day. There are no natural enemies to keep it in check, no wildlife to eat it and no other plants being that can contend with its all-conquering growth. 

What does Japanese Knotweed look like?

Now you know that this plant is your enemy, it’s time to seek and destroy. Japanese knotweed identification is not the easiest task. However, the plant does have some recognisable features that you should look out for.

Japanese knotweed, otherwise known as Fallopia japonica, differs in appearance depending on the time of the year. Its growing season tends to run from April to October, but the UK’s mild and damp climate means that it can run from as early as March to as late as November, giving the plant a longer havoc-wreaking window.

Despite its differing seasonal appearance, the plant is commonly known for its spade-shaped leaves and bamboo-like stems. In spring, it can be compared to an oversized asparagus, with the knotweed spears capable of reaching 3 metres in height. These spears then develop into green bamboo-like canes and grow leaves. In the summer, watch out for Japanese knotweed flowers: small, white and growing on its leaves.

While Japanese knotweed will continue to grow throughout the summer and into the autumn, it becomes dormant in the winter. The leaves drop off and the canes turn dark brown and begin collapsing on top of one another. However, do not be deceived. Although Japanese knotweed may look dead in winter, it’s simply waiting for warmer weather, with new shoots underneath the leaf litter waiting to emerge and expand.

How can Japanese Knotweed damage your property?

As mentioned, Japanese knotweed can cause major damage to buildings and other structures. The underground roots exploit any cracks or weaknesses in a structure and the pressure exerted by their expansion can result in serious damage. Such is the strength of Japanese knotweed, it can push through tarmac, paving stones and brick.

Sometimes the ravages of Japanese knotweed can’t be seen until the damage is done. As the roots search for moisture, they can infiltrate drainage pipes and other underground infrastructure. This encroachment can lead to blockages and lifting pipework. It can also lead to blackouts and electrical complications. In worst-case scenarios, drains and pipes will have to be completely replaced, something which is extremely costly.

If, for whatever reason, you decide to tolerate Japanese knotweed on your property, the law is very clear about how this should be handled. Japanese knotweed is not illegal. But you do have a duty not to allow it to grow onto neighbouring properties. If your knotweed grows out of control and encroaches other properties, it will be classed as a ‘private nuisance’ and you may be prosecuted under civil law, resulting in some serious financial penalties. For reference, a private nuisance is an act or omission that interferes with, or otherwise disturbs, a person’s enjoyment and exercise of their ownership of land. One such example of knotweed becoming a private nuisance was when a homeowner in Wales was awarded £15,000 in damages after an infestation of Japanese knotweed on National Rail land encroached on his property.

Implications When Buying or Selling a Property

When it comes to buying and selling property, Japanese knotweed is a headache for both parties. For sellers, the discovery of Japanese knotweed on their property can scupper a deal and leave them with nothing. For this reason, it’s recommended to hire a reputable firm to carry out the extermination of the plant before you list your property for sale. While this may be costly, this is certainly the lesser of two evils: many buyers, and their lends, won’t touch a property riddled with knotweed due to fears over the property structure, complications and repair costs.

It’s also worth noting that both the seller and the estate agent have an obligation to disclose the presence of knotweed. In agents’ case, consumer protection regulation requires them to inform the buyer of any material facts that might impact their decision to buy, and Japanese knotweed counts as ‘material’ in this case.

For buyers, Japanese knotweed can ring the knell of their home-ownership dreams. Many mortgage providers simply will not lend if the property survey comes back with Japanese knotweed. While some lenders may take a more pragmatic view and lend the money on the condition that the knotweed will be eradicated by a reputable firm, others will flat out refuse to do so. In these cases, the mortgage lender may refuse to accept any mortgage application from the would-be buyer until the seller sorts the problem out.

If Japanese knotweed is not treated properly, its impact on a properties market price can be massive. Due to a reluctance to lend on properties with knotweed, it’s common for sellers to end up selling the property at well below their initial asking price, or to cash buyers in market for a bargain. In fact, for one homeowner in Cheshire, they were looking at a potential £30,000 loss on their property due to the presence of Japanese knotweed.

When it comes to knotweed getting in the way of a potential purchase, it’s always recommended that the buyer and seller work together to find a solution. Not only will this give the buyer comfort in the work being taken out by a reputable company, but it will also help them get their mortgage. Meanwhile, the seller will get a fair price on the property

Japanese Knotweed Removal

So now we’re onto the $1million question: how to get rid of Japanese knotweed. This is a complex and challenging procedure best undertaken by a reputable and specialist company. This said, there are some people who prefer to go it alone and take on the plant with a DIY approach (more on this below).

Japanese knotweed removal is particularly tough due to the plant’s notorious ‘bouncebackability’. Even if one tiny shoot of knotweed is left behind, the plant will grow back to its full extent and cause exactly the same problems. For this reason, all work carried out needs to be extremely thorough, and checks should be done to ensure no remnants of knotweed are left on the property.

There are many removal methods, causing Japanese knotweed removal costs to vary widely. The most common approach is to use herbicidal stem injections. The most economically friendly removal technique, this method can take between 24 and 48 months to be completed, with two to four growing seasons being required to ensure that Japanese Knotweed is thoroughly eradicated. Depending on the size of your land, herbicide treatments can range from £1,000 to £12,000 in price.

If you require immediate treatment, excavation may be your best bet (although it will come at a cost). Using a root barrier during excavation will prevent the Japanese knotweed from spreading onto neighbouring properties as its roots will not be able to penetrate the barrier or continue to expand. Japanese knotweed roots tend to grow 2 metres deep, so by digging 3 meters below the ground, the barrier will completely surround the infestation. This should rule out any legal proceedings from neighbouring properties in the future.

Professional contractors will ensure that the barrier is installed at an angle of 45º, so that any root growth from outside the barrier will be diverted downwards rather than punching through and causing an infestation leak. As mentioned, this treatment is more expensive than herbicides (costing anything between £2,000 and £35,000) but it can be carried out as a matter of urgency and eradicate the problem promptly.

Whether it’s down to money or personal pride, some people decide to take on their infestations single-handedly.

DIY Japanese Knotweed Treatments

If you’re taking on the beast yourself, be sure to have done your research first. As a rule of thumb, it’s best to start the treatment as soon as possible (to prevent the infestation spreading) and to understand the science behind the herbicide treatment. Failure to do so could have heavy implications for your home and your finances in the future.

You will need to dig deep enough to reach the end of the root and carry out the treatment to an industry standard. Don’t flail the knotweed, don’t spread contaminated soil and, whatever you do, do not allow any soil or plant parts to land on neighbouring properties.

What does Japanese Knotweed Mean for my Home Insurance?

Despite it being a (fairly) common issue, most home insurance policies will not cover costs related to the damage or removal of Japanese knotweed.

While this does mean you won’t have to pay a higher premium should you have a knotweed infestation, it also – sadly – means that you will have to pay for any knotweed treatments out of your own pocket. However, if your knotweed infestation impacts a nearby property, your home insurance may cover the costs of any claim made against you – however, you will need to check that this is the case with your policy. If not, this can kind of cover can generally be bolted on.

Lastly, when it comes to professional Japanese knotweed removal, check to see if the company you have employed offer any kind of guarantee. With the backing of insurers, many removal firms will offer not just to remove your knotweed once but to eliminate – at no extra cost – any recurrence within a given time period (10 years, for instance). Most companies will offer this service for around £200 – an additional charge that may be annoying but will at least give you peace of mind should the dreaded knotweed return.


Japanese knotweed is a plant that a lot of people have never heard of. But those who have are unlikely to ever forget the ordeal of having to deal with it. The plant is an absolute nuisance and can wreak havoc on your property, any potential house sales and your overall financial situation. If you suspect that your property has a Japanese knotweed problem, it’s always best getting a professional opinion and researching the most reputable and affordable companies before you carry out any work.