What damage can Japanese Knotweed do?

Where did Japanese Knotweed come from?

Japanese Knotweed began its UK staycation in the 1850s when it wowed Victorian botanical with its exotic appeal and was a welcome guest in any well-to-do garden. But with gardening trends being what they are, this horticultural flavour of the month was soon discarded and its resilient roots were discards by the wayside.

How did Japanese Knotweed become a problem?

Little did the gardening gurus of the day know, they were actually unleashing a fiendish devil weed into the wild, since Japanese Knotweed can regrow from just a 2mm fragment of root, and that’s just what it did. The inhospitable rocky terrain of the quarries and roadsides where it was dumped were nothing to this voracious vine that found its origins on the hostile slopes of volcanoes in Japan.

What does Japanese Knotweed look like?

The pesky plant isn’t always easy to identify, and although it can look similar to bamboo, they are not in the same family. You’ll know Japanese Knotweed by its spade-shaped leaves, which can grow up to five and a half inches in length. During the late summer, it can also be identified by its creamy-white flowers. To see what Japanese Knotweed looks like, check out our photos and pictures of Japanese Knotweed page.

What damage can Japanese Knotweed do?

On its never-ending search for growth and sustenance, Japanese Knotweed can grow through brick walls and even concrete when it finds a weak spot. And as it makes its way, it’ll cause untold damage to buildings, foundations, pavements and even invade houses if they get in its way.

The power and speed of Japanese Knotweed would almost be something to admire if it weren’t for the destructive nature of this villainous weed. Ever eager to expand its territorial domination, Japanese Knotweed weed will infiltrate the tiniest of cracks and wind its wily way through drains and underground sewers.

Combined with its tenacity and resilience, Japanese Knotweed brings a rapacious growth which makes it a truly unwelcome garden guest and an even less welcome house invader if you’re unlucky enough. Able to grow up to 10 cm a day, Japanese Knotweed will target weak spots in buildings, crack masonry, split pipes and ravage foundations if left unchecked. And it shows no respect for fences and boundaries either, eagerly spreading from one garden to the next above or below ground.

  • Underground services – With its insatiable thirst, Japanese Knotweed will worm its way into pipes through tiny cracks or joints, and from there it will expand locking the pipe and eventually breaking it.
  • Hard surfaces such as asphalt – This is the Japanese Knotweed damage we see most often. Asphalt, patio slabs, driveway block paving will pose no problem to Japanese Knotweed on its unstoppable quest for light. Basically, if water can drain down into it, Japanese knotweed can grow up through it.
  • Concrete – It may be strong but not even Japanese Knotweed can grow through concrete. It normally finds a weak spot, pushes through and then expands as it goes to cause damage.
  • Buildings – If left unchecked for long enough, Japanese Knotweed can establish itself and wreak havoc on residential and commercial properties.
  • Boundary wall – Again is left unchecked, Japanese Knotweed will grow with enough force to damage fences and even cause walls to fall.
  • Cavity walls – Japanese Knotweed will grow up and through vents and air bricks two metres above ground, and once it’s in cavity walls it has the force to push the two skins of the wall apart.

Letting Japanese Knotweed spread

Failure to control Japanese Knotweed on your property, and letting it spread to a neighbour’s garden can now lead prosecution and quite a hefty fine for anti-social behaviour as well.

Schedule 9, Section 14 of the Wildlife and Countryside Act 1981 states that “if any person plants or otherwise causes to grow in the wild any plant which is included in Part 2 of Schedule 9, he shall be guilty of an offence”. (Japanese knotweed is a Schedule 9 listed plant).

But updates to the guidance documents now specifically name Japanese Knotweed alongside Himalayan Balsam and Giant Hogweed as a source of “serious problems” and state that individual failing to control the troublesome triffid will have committed a criminal offence and be liable for a fine of up to £2,500. Not sure if it’s knotweed? Check out our article on plants that look like Japanese Knotweed.

Williams and Waistell v Network Rail: claiming damages for the spread of Japanese Knotweed

In 2013, Stephen Williams and Robin Waistell, two residents in South Wales made a claim against Network Rail, which owned the land immediately behind their properties. Japanese Knotweed had been present for at least 50 years on the land owned Network Rail. The neighbours complained about the encroachment on to their land, and were awarded damages when the judge ruled Japanese Knotweed as a natural hazard affecting landowners’ ability to fully use and enjoy their property. More detail of Network Rail Infrastructure Limited v Stephen Williams and Robin Waistell judgment.

Smith v Line: The cost of allowing Japanese Knotweed to spread

If you notice Japanese Knotweed growing in a neighbour’s garden, it is their responsibility to control it and make every effort to ensure it doesn’t encroach into your property or another neighbour’s. Failure to do this means they can be held responsible for damages caused by this pernicious patio pest.

A case earlier this year between two neighbours was resolved after thirteen years, when a judge ruled Ms Line had allowed Japanese Knotweed to encroach onto the Smith’s property and as a result the value of the claimants’ land had been reduced by 10%, from £800,000 to £720,000. Ms Line was ordered to employ reputable contractors over the next five years to eradicate the agricultural interloper and also to pay court costs. See more details of Smith v Line Japanese Knotweed case.

Surveying and Removing Japanese Knotweed

If you do suspect an infestation of Japanese Knotweed on your or your neighbour’s property, you can send us a photo for a free, no obligation check.

Once Japanese Knotweed has been identified, you should tell your neighbours about it straight away and let them know that it is their legal responsibility to have the nefarious weed eradicated. Then you should let them know about Japanese Knotweed Specialists, one of the UK’s leading contractors and consultants in the control, treatment, removal and thorough elimination of Japanese Knotweed and that they can contact us here or give us a call on 0800 122 3326.


Our house purchase was held up when we were refused a mortgage at the valuation stage, when a survey commissioned by the bank showed that Japanese Knotweed could be present on the property. This really slowed down the process. It feels like an unreasonable extra expense and an unnecessary cost. Thankfully, Japanese Knotweed Specialists charged a very reasonable fee to carry out a Japanese Knotweed survey to find there was in fact no trace of the weed on the property, so the sale could go ahead. Thank you Japanese Knotweed Specialists. Property developer Peri, London
We recently purchased a property in the Bromley area. The initial mortgage valuation survey reported the presence of Japanese Knotweed growing on the railway embankment at the end of the garden. The mortgage lender advised that before they would consider approving our mortgage application, we would need to hire a JK specialist to inspect the growth and provide a detailed report on the findings. We duly approached Japanese Knotweed Specialists and Adam came round to carry out a survey. Thanks to his full and detailed report on the Knotweed, our lender was satisfied and (subject to a treatment programme being implemented) approved our application and we were able to proceed with the purchase. Japanese Knotweed Specialists have now commenced their 1st treatment to eradicate the JK and their service is always friendly and helpful. Mr Winsor, Bromley
Many thanks for such a speedy turnaround of this report. As I said yesterday, this has been an extremely worrying time for us, but the efficiency, professionalism and helpfulness shown by you and Tanya has been second to none, and has made a difficult situation that bit easier to handle. Arleen, Derby

We operate nationwide including but not limited to London, Manchester, Birmingham, Brighton, Leeds, Cardiff and Surrey.