What is Japanese knotweed?

Officially titled Fallopia Japonica, Japanese Knotweed is a plant native to east Asia. It arrived in Europe during the 19th century, and unaware of its ability to cause harm it was planted freely. It was even celebrated for its pretty flowering branches!

Sometimes mistaken for bamboo, Japanese knotweed grows from rhizomes that are situation deep underground. Roots from these rhizome bulbs can spread as much as 3 metres deep and up to 7 metres across. Above ground, the plant can grow up to 10cm a day, reaching heights of 2-3 metres.

It’s typically found on riverbanks, railway sidings, development sites, residential gardens, roadsides, woods and footpaths. Aside from root growth, it can also spread through contact – small pieces of the plant can be picked up and transferred by fly tipping, handling of garden waste and in the soles of shoes. In the case of railway sidings, the plant was used to screen for sound from neighbouring properties without realising that the trains had the capacity to carry the plant to new areas.

But it’s not all bad – the plant can be used to create cattle feed, soup, wine and even ice cream!

Japanese knotweed is believed to affect 4% of homes in the UK.

How to spot Japanese knotweed

The appearance of Japanese knotweed varies of the course of the year, as the plant natures through the seasons. It’s often said to represent asparagus.

In Spring – bright red bulbs and reddish purpose shoots

Summer – hollow reddish-green stems with deep green leaves

Impact of Japanese knotweed

Japanese knotweed has a bad reputation in property circles, understandably so. The roots and branches grow at a phenomenal rate and with great strength. Issues include:

  • Large green leaves block the light of other native plants, dominating the space and thriving whilst causing native plants to retract and potentially die off.
  • Developers dislike the plant because of the high cost of removal. Presence of knotweed requires extensive excavations because of how far reaching the root system can spread, having to go both deep into the ground and several metres in all directions.
  • The plant is strong enough to break through decking, patios, concrete, foundations and even through the flooring of a home in its search for moisture, exploiting all weaknesses.
  • The disruptive root system affects services, walls, foundations, conservatories and flooring.
  • People have been unable to successfully sell their homes, or their homes have been significantly undervalued where Japanese knotweed is present.

So why is this not a problem in its native Japan? In Japan the plant is vulnerable to local pests and diseases which have controlled its activity. Some European countries are exploring introducing some of these species to test the effectiveness on reducing Japanese knotweed spreading. Other companies have taken an alternative approach, training dogs to sniff out the plant and root.

FACT: There’s no statutory requirement to remove or kill the knotweed plant. It is, however, the owners job to be responsible for it not spreading.

Regulation and liabilities with Japanese knotweed

There are several pieces of legislation which come into force when considering Japanese knotweed:

Wildlife and countryside act 1981 – covers the spread of non-native species. If found guilty of allowing knotweed to grow and cause problems for others, under this act individuals can be charged with a fine of £5000 and 6 months in prison – or 2 years in prison and an unlimited fine.

Environmental protection act 1990 – along with the Wildlife and countryside Act, this act covers the disposal of knotweed. The problem plan can only be taken to landfills licensed to handle contaminated soil. Untreated knotweed is not a classed as hazardous waste, but treated knotweed could be – it is the responsibility of the person collecting and transporting to a licensed handler to get it right.

Anti-social behaviour orders (ASBO) – police can take action, serving an ASBO against businesses and individuals who don’t control Japanese knotweed when could be reasonably be expected to do so.

Declaring Japanese knotweed in form TA6.

In February of 2021, the Law society made changes to form TA6 s7.8. It is now a requirement for sellers to declare with absolute certainty whether Japanese knotweed is or isn’t present – adding in an “unknown” response.

In order to answer “no” to the presence of knotweed, sellers MUST be certain in saying it is not found above or below ground, within 3m of a property. Because the root system of knotweed can’t be seen and can travel extensive distances, it’s virtually impossible to know it’s not there. Because the seller will be liable for the response given, it’s important that they understand the implications to responding on the form.

To help prevent your clients being left open to legal action, we offer client care text which explains each of the yes/ no /not known responses and implications. Do please speak to one of our team if you would like a copy.

Eradicating Japanese knotweed

The good news, it is possible to get rid of Japanese knotweed. Options vary in both cost and time involved, with the main routes taken including:

  • Excavation and landfill of the site. This can take 1-2 weeks and involves digging out all contaminated soil and root system. Understandably, this makes it the costliest route but also the fastest. Most suppliers offer a ten-year guarantee insurance.
  • Foliar spray – In this process, herbicides are applied to top and underside of the leaves. Absorbed by plant, the herbicides reduce the ability of the plant to regenerate. Whilst significantly cheaper than excavation, it will take approx. 3 years to fully die back.
  • Stem injection. This involves preventing regeneration by taking herbicides and injecting them directly into the stem system of the plan. The benefit over foliar spray is that there is less chance of transmission of the herbicides onto neighbouring plants. It will still take over 2 years for the plant to die back.
  • Both foliar spraying and stem injection require the land to lie dormant for several years, making it unavailable to landscaping.

Do surveyors find Japanese knotweed?

Whilst surveyors will take every measure possible, given the distances the root systems can travel underground it’s hard for surveyors to confidently identify what’s in the area of a property. It would require gaining access to multiple surrounding properties, over significant periods of time, to be certain of spotting the plant in all of its growing stages. The plant is especially difficult to spot in the very early stages of growth, and in the winter can easily mistaken for looking dead.

What we do know is that when surveyors have confirmed the presence of Japanese knotweed, the valuation can be reduced by significant amounts. It’s common practice to offer a number of valuations based on the various method for eradicating the plant, due to the time taken for the different methods to take effect.

Japanese knotweed indemnity policy

CLS offers a Japanese knotweed indemnity policy designed to protect buyers, lenders, landlords and successors for 5 years.

The policy is available for both residential and commercial properties, up to 0.5 acres in size and offers an indemnity limit of £20,000.

Available from our website, the policy can also be adapted online using Variable Statements of Fact, to customise to your client’s needs.

And finally… Bohemian knotweed

A hybrid plant formed from Japanese knotweed and Giant knotweed, this plant behaviours similarly to all the information we have discussed here but more aggressively. Achieving growth of 2-3 metres per day, with larger leaves and spread through the air in addition to contact, the plant is a significantly more vigorous variant.

Of the 4% of properties in UK affected by Japanese knotweed, it’s estimated that 2% are affected by bohemian knotweed. The good news is that it’s also covered by our Japanese knotweed policy, so we have your covered.

Click here to start working with us.


This article was submitted to be published by CLS Property Insight as part of their advertising agreement with Today’s Conveyancer. The views expressed in this article are those of the submitter and not those of Today’s Conveyancer.

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