Buying a house with Japanese knotweed

... a buyers guide



August 03, 2022

Japanese knotweed aside, buying a house is an expensive and emotional experience. So, is it really worth investing in your dream home if Japanese knotweed is present? 

Here's our guide for home buyers who've found their dream home but also the dreaded Japanese knotweed - seven things to consider.

Garden with Japanese knotweed infestation

Is it worth buying a house with Japanese knotweed?

Buying a house with Japanese knotweed can be worth it if it is your 'dream home'. However, home buyers and property developers should understand that it takes a lot of time, money and patience to eradicate this invasive plant from any location. 

  • Consider the possibility of damage to the property (house, garage, outhouses, etc.,);
  • Costs associated with Japanese knotweed removal;
  • Restricted access to the garden;
  • Problems with the new neighbours;
  • Legal implications;
  • Diminution;
  • Mortgage issues.

In this guide, we discuss these seven problems to help you gain insight into whether or not purchasing a property with a Japanese knotweed infestation is the right choice for you.

Japanese knotweed property damage

Yes, Japanese knotweed can damage your property. This is especially true if the infestation is extensive and lies close to the house. And yet even a small growth at the end of the garden can turn into a monster 'homewrecker' if given enough time and the right conditions. In fact, Japanese knotweed will exploit weaknesses in drains, pipes, garden walls and fences, driveways, concrete, patios and even the foundations of conservatories and outbuildings. Scary, right?

What’s even more alarming is that Japanese knotweed can lurk three metres below the surface of your garden – an invisible enemy. So, before you seriously consider purchasing a house with Japanese knotweed, hire a RICS chartered surveyor to do a survey. The surveyor will advise on the current size of the infestation and likely growth rate in the future.

consideration when buying a house with Japanese knotweed

Residential property with Japanese knotweed infestation.

small garden with japanese knotweed

Small garden affected with Japanese knotweed.

japanese knotweed infestation at residential property

Knotweed growing close to buildings causes untold damage and expense.

Japanese knotweed removal costs

Japanese knotweed removal costs vary depending on the method that's required - the cheaper removal solution starts at around £3,000. Sadly, 'Round-Up' won’t do the trick! In fact, DIY attempts to remove this invasive plant can make matters worse by spreading it to neighbouring land or waterways .

Often, the property seller will have a herbicide treatment management plan in place, something which usually lasts three years. But if they haven’t taken care of the issue, the ball is now in your court to get the knotweed removed.

Generally, the two main knotweed removal methods to choose from are:

  1. Herbicide Treatment - with this solution a Japanese knotweed professional will spray the knotweed in the summer over a period of about three years. This is the cheapest option and usually picked for residential infestations, where excavation would be difficult. 

  2. Excavation -  This involves bringing in professional plant vehicles to dig up the Japanese knotweed and take it to a licensed landfill site. Typically, excavation takes place over a week or so, depending on the size and density of the infestation.
All in all, if you want to buy a house with Japanese knotweed you have to consider the time, hassle and costs involved with removing it. It might also be worth asking the seller for a reduction on the cost of the house to cover the removal costs. Or, you can insist they initiate and pay for a knotweed treatment plan up-front. Usually, your solicitor will be able to help navigate these murky waters – just make sure you get an insurance-backed guarantee to cover you for the future.  

Oh, and another thing, never fall into the trap of the seller telling you (verbally) that they’ll “sort out the knotweed” before you move in. Remember, if a promise is not down on paper – a legal one – don’t trust it.

Restricted access to your garden

Japanese knotweed spreads easily. In fact, a fragment the size of a 'Tic Tac' can grow into a large infestation. This is why it’s essential to reduce the spread of Japanese knotweed wherever possible, or risk an even mightier problem! Normally, we strongly recommend you cordon off the infested area by up to three metres.

In principle, this seems fair enough -  why not reduce the spread of the pest? However, the reality can be far more frustrating. For example, young children and pets are notorious for accidentally spreading the plant further afield. Dogs pay no heed to a no-access sign! Before you know it, they have caught fragments in their paws and carried them all over the garden. 

What’s more, a three-metre buffer zone can take up a large part of your garden. You will have to accept that much of it will be unusable for a good period of time, often three years if the knotweed is under a herbicide treatment plan. Remember, herbicides can also irritate your skin and eyes.

Whatever you do, ensure your 'no-go' Japanese knotweed zone is properly cordoned off. If you have pets or young children, consider a physical barrier. Good luck!

Problems with neighbours

Having an easy relationship with your neighbours is a key ingredient to being happy in a new home. Yet, the relationship is often fraught with peril. Park in “their spot” on the street and you’ll soon find out!  So, having a Japanese knotweed infestation on your side of the fence – or theirs – can cause untold trouble.

It’s important to remember that allowing Japanese knotweed to spread beyond your garden is illegal. So, if your infestation is encroaching into your neighbour’s garden – causing them to forego the enjoyment of their own garden whilst also reducing the value of their property – you might be in for some hard times ahead. But, the same applies in reverse. Should their Japanese knotweed be invading your garden, you should expect them to take steps to remove it. If not, you will be well within your rights to sue them. Either way, the situation is a bundle of joy (not).  It will certainly help your relationship with next door if you can show you’re having the knotweed removed or treated.

Japanese knotweed causing damage to garden buildings, houses, outbuildings

Large infestation of Japanese knotweed close to buildings.

Development site with Japanese knotweed growing

Development site with Japanese knotweed growing.

Cordon off affected area during herbicide treatment

Cordon off affected area of land during herbicide treatment.

Legal implications

Japanese knotweed can get you in trouble with the law. This is because it is a criminal offence to “allow Japanese knotweed to spread from your property into the wild” (Wildlife and Countryside Act 1981). So, here are the legal implications to consider:

  • As the new owner of the property, you will legally inherit the responsibility for the Japanese knotweed.

  • Law enforcement can slap you with a Community Protection Notice (CPN) and consequently an ASBO (Anti-Social Behaviour Order) to force you to control the knotweed on your land.

  • Failure to control the knotweed can see you facing fines of £2,000 or even a short prison sentence.

  • It’s also illegal to dispose of Japanese knotweed clippings in any household waste bin (including compost and “green” garden waste bin).
It’s worth thinking about the legal implications of owning a house affected by Japanese knotweed. Taking steps to remove it is a good way to avoid penalties.


Diminution can occur when a property is affected by Japanese knotweed. This means the value of your house may drop by 10 or 15 percent. Yikes! 

Usually, property diminution is a problem for sellers. However, it can affect buyers too. It’s worth asking the estate agent and your solicitor if:

a)     The property has already received a reduction in value (if not, it might be something to ask for if you’re taking on a house with infestation included).

b)     It’s likely your property will still face diminution in the future, after it’s removed.

Many factors determine whether or not your dream property will have the value knocked out of it! So, forewarned is forearmed in this case!

Japanese knotweed and mortgage issues

You will struggle to get a mortgage on a property affected by Japanese knotweed. It’s so unfair, but this invasive weed makes most mortgage lenders run for the hills without a backwards glance. 

Thankfully, it is not the end of the road for you and your dream home. Difficult though it may be, now you will have to hop, skip and jump your way to getting your mortgage approved. 

Firstly, some mortgage lenders are more accepting of Japanese knotweed than others, meaning you’ll have to shop around. Secondly, to get approval, a fully paid-for treatment plan must be in place by a qualified Japanese knotweed company. Thirdly, the same company must issue you with an insurance-backed guarantee, so if the knotweed comes back, you are covered. Finally, the “risk factor” of the Japanese knotweed infestation will also determine how successful you are in getting a mortgage.

Make an informed decision

So, is it worth your time and money to buy a house with Japanese knotweed? We can’t answer that question for you. However, we hope this guide will help you make an informed decision.

It is worth noting that 32% of people still commit to buying a house with Japanese knotweed. So this pesky plant doesn’t have to be a deal breaker in purchasing your ideal home, but there is a lot to consider, and take on. 

Contact us today

For over 20 years we have been helping homeowners and property developers tackle Japanese knotweed. To discuss your knotweed concerns get in touch via our contact form, and if you have photos of the infestation, please attach them to your correspondence as they will help us understand the size of the job and confirm identification right from the very start.