This week’s blog is all about Japanese knotweed and how it could affect you if you are buying or selling a property – or even if you’re staying put! According to recent research, Japanese Knotweed has knocked £20 billion off the total value of the UK property market, with many mortgage lenders refusing to approve funds for homes which are affected by this virulent shrub.

What is Japanese Knotweed?

Japanese Knotweed (Fallopia Japonica) was first brought to the UK in the 1850s as an ornamental species. Its strong roots and vigorous growth meant that it was also popular for use in stabilising the ground at railway cuttings, during the burgeoning age of steam and it was initially very popular amongst Victorian horticulturalists and industrialists alike. Unfortunately this popularity soon waned once people discovered that the plant was able to grow through tarmac, concrete, drainage systems and brickwork – causing destruction to homes and gardens and spreading like a wild weed. Japanese knotweed is now one of the UK’s most destructive, aggressive and invasive plants. It is also notoriously difficult to remove.

Last year a survey by YouGov and knotweed specialists Environet, found that some 5% of homes in the UK are currently affected by knotweed – either directly or from neighbouring properties.

Speaking to the Independent about the knotweed invasion, Nic Seal, the founder of Environet suggested that the problem is not likely to be fixed overnight and that it is something that all homeowners and potential buyers must be aware of:

“Japanese knotweed is the problem that just keeps growing. For most people in the UK, their home is their biggest asset and often the ‘pot of gold’ they are relying on in retirement, but Japanese knotweed is having a serious impact on values by deterring buyers and making homes difficult to sell, even if the knotweed has been successfully treated,”

If a home is affected by knotweed in can wipe at least 10% off of the price and with an estimated 850,000 to 900,000 UK households affected by the weed, this would mean that it has wiped almost £20 billion off of UK house prices.

Japanese Knotweed

Not your problem?

If you have knotweed on your property and you don’t think it is a problem, think again. Landowners can be sued if they allow it to spread next door.

Speaking about the challenges involved in removing knotweed, Marc Montaldo of Cobley’s Solicitors – who specialise in Japanese knotweed litigation – suggests that if your knotweed strays, you can be liable for quite a large pay out to your neighbours:

“In legal cases relating to diminution in value due to knotweed, we typically see claims for around 10 per cent of the property’s value. This is due to the stigma attached to knotweed impacting its future sale price.”

Sellers are legally required to let future buyers know if their property is or ever has been affected by Japanese knotweed – even if it has been successfully removed – and mortgage lenders might refuse to provide a loan for a new home unless there is a knotweed management plan in place, with a guarantee backed by insurance.

Japanese Knotweed

So what can you do about knotweed?

If you have knotweed. Firstly. Don’t try treating it yourself – this can actually make things worse and it could potentially spread even more quickly. There are quite a few specialist knotweed removal firms out there so call an expert and get it done properly.

If you move into a property with a knotweed problem where the owner ha s obviously withheld information from you, then you may be entitled to sue, but this is shutting the door after the horse has bolted. The best thing to do is check for any reported cases first and Nic Seal from Environet has created an incredibly useful UK knotweed heatmap, showing all of  reported cases, which is updated regularly:

“The site is already well populated, but this is an ongoing project. The more people who report sightings, the more effective it will become. His is also be a useful tool for homeowners who want to be aware of infestations near their property which could spread, putting their home at risk,” he said.

The map shows that Dorset is relatively safe from the dreaded shrub, with only 6 reported cases within 4km of our headquarters here in Bridport. If you’re concerned about knotweed before you move then you can check out the map here: You can also report any cases of knotweed and help contribute to the heatmap project and there are also some useful tools on the site to help you to identify Japanese knotweed, which is often mistaken for other shrubs such as Himalayan honeysuckle.

Japanese knotweed picture credits:
H. Zell [CC BY-SA 3.0 (]
KENPEI – KENPEI’s photo, CC BY-SA 3.0,