Originally brought to the UK in the Victorian era as a quick-growing ornamental plant, Japanese knotweed has turned into a nightmare for thousands of homeowners across the UK.

Known for its fast growth rate and incredible longevity, it has become one of the most common invasive plant species in the country. If left untreated, or treated improperly, Japanese knotweed can cause serious structural damage to homes and drive down their value – which in turn can make them hard to sell or get a mortgage on.

This guide contains everything you need to know about Japanese knotweed – how to spot it, what you can do about it, and how to get a mortgage if you think it might be growing near a property you want to buy.

How to recognise Japanese knotweed

Japanese knotweed can grow in just about any kind of soil, and is commonly found on roadsides, railway embankments, and along rivers and streams.

The plant itself is characterised by dense clusters of green, purple-speckled bamboo-like stems which can grow several metres tall and are hollow on the inside. The leaves are generally shaped like hearts or shields, with a pattern that alternates on either side of the stem. Small white flowers can grow on the plant between July and October.

Get expert mortgage advice*

Looking to discuss your mortgage options? Rest Less members can book a free mortgage consultation from Fidelius. Speak with a qualified, FCA-regulated, independent mortgage adviser you can trust. Rated 4.7/5 on VouchedFor from over 1,000 reviews.

Get mortgage advice*

Why is Japanese knotweed so bad for homes?

Japanese knotweed is notorious for the structural damage it can wreak on homes. It can crack tarmac, spoil patios and paving, block drains and even damage the walls and foundations of a property.

Not only this, but the plant is incredibly hard to get rid of. Knotweed roots spread very quickly and can grow several meters underground. Destroying Japanese knotweed yourself is almost impossible, and more often will just make the problem worse. Stephen Hodgson, the chief executive of the Property Care Association (PCA), advises that “digging it out of the ground can just spread it terribly”, as the plant is capable of regenerating itself from the tiniest remains. Entirely new plants can grow from shreds of just 1cm in size.

This combined with its growth rate – up to 10cm a day in the hotter months – means it’s not hard to see why lenders are so nervous about providing mortgages on homes where Japanese knotweed is present, or a risk.

How do you get rid of Japanese knotweed?

If you find Japanese knotweed in your garden or growing nearby, then the most important rule is not to try and get rid of it yourself.

There are companies that specialise in treating cases of Japanese knotweed. Before contacting one, check to see if it is a member of the Invasive Weed Control Group of the Property Care Association or the Invasive Non Native Species Assocation (INNSA). The INNSA offers a directory of members including relevant contact details.

The company you choose will typically inspect the problem and work with you to figure out a plan to remove the knotweed, though this is rarely a quick or straightforward process. The most common solution is the routine use of industrial-strength herbicides on the knotweed, which normally takes around three years to complete. The cost of contracting a specialist company will depend on the company and the severity of your knotweed problem, so you should make sure to compare quotes from a few different contractors.

If you have cut down any of the knotweed, this must be disposed of on-site. This means you need to compost it separately on plastic sheets. You should not take Japanese knotweed or even the soil in which it grows to the dump or attempt to get rid of it in the wild, as this is likely to spread it.

You don’t legally have to remove knotweed from your own property, but you can be prosecuted if it spreads into the wild or even sued if it spreads into a neighbouring garden.

Will a surveyor warn me about Japanese knotweed?

If a property has a knotweed problem, you ideally won’t have to wait until the surveying stage to find out – sellers are legally obliged to declare the presence of knotweed when they sell. However, they will sometimes claim to be unaware of the plant or may attempt to conceal it during the sales process. 

With the plant becoming more common, surveyors are increasingly able to spot the signs of knotweed while conducting a survey of a property. If they think the home might have a knotweed problem, they should let you know how serious the issue is and recommend a cause of action.

You can find contact details for RICS surveyors in the area you’re buying using the RICS Find a Surveyor service and find out more in our guide Which property survey should I get? 

Will Japanese knotweed affect my mortgage application?

Homebuyers should tread carefully when buying a home with a knotweed problem. Lenders tend to be very nervous about offering mortgages on homes where Japanese knotweed has been found growing nearby, since the potential structural damage it can cause can hurt a property’s resale value immensely.

Teddy Cenaj, mortgage expert at Rest Less Mortgages, says: “Lenders are normally not too keen on properties which are affected by Japanese knotweed. However, it is not impossible to get a mortgage. Some lenders are willing to consider applications on affected properties but initial treatment will need to begin before getting a mortgage confirmed. Sometimes lenders will also retain some of the mortgage until the buyer can prove that they have successfully eradicated the plant.”

Want to speak to a mortgage advisor? Speaking to an experienced mortgage advisor can help you to understand your options and get a great deal on your mortgage.

If you’re looking for expert mortgage advice, you can get a free consultation with an independent mortgage adviser at Fidelius. Speak with a qualified, FCA-regulated, independent mortgage adviser you can trust. Rated 4.7/5 on VouchedFor from over 1,000 reviews.

You can read about other things that might make it harder to get a mortgage in our article 10 reasons you might not be able to get a mortgage on a property.

Does home insurance cover Japanese knotweed?

Most buildings insurance policies won’t cover damage caused by Japanese knotweed, and therefore you usually won’t be able to make a claim to help get it removed, but check your policy small print to see exactly where you stand. If your home is affected by knotweed originating on a neighbouring property, your insurer may well pressure them for compensation.

You could consider getting indemnity insurance if you are buying in an area with knotweed risks where the property itself is currently unaffected, or if you are buying a property that has had knotweed in the past but no longer does. This should cover some or all of the relevant costs of treatment if Japanese knotweed affects the home in the future, including any repairs to the property and legal bills if the knotweed spreads to other properties and your neighbours take action against you.

Rest Less Money is on Instagram. Check out our account and give us a follow @rest_less_uk_money for all the latest Money News, updated daily.