Japanese knotweed

How to deal with problems associated with Japanese

knotweed (Fallopia Japonica)

A guide to Japanese knotweed

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What is Japanese knotweed?
Japanese knotweed is one of a number of invasive plants that can cause problems to your property:

  • It’s a large clump-forming plant, which grows up to 3m tall, with light green shield-shaped leaves with a flattened base, approximately 10-15cm long.
  • The stem is hollow, bamboo-like, light green speckled with pink-red.
  • There are only female plants in Britain, so no viable seeds are produced.
  • The flowers are tiny and clustered together in creamy-white sprays, present from August to October.
  • It produces thick and extensive roots called rhizomes, orangey-yellow inside, and spreads by fragments of rhizome. A piece the size of your thumbnail is sufficient. Fragments of rhizome get picked up in soil and on equipment.
  • Over the winter the plant dies back leaving tall brown canes but as a perennial plant its top growth is renewed each year from the rhizomes which can spread relentlessly.

What are the problems caused by Japanese knotweed?
You can have Japanese knotweed growing on your property and, unless required to do so under a Community Protection Notice (see below), there is no requirement to take any action to deal with it. It would however be advisable to take measures to eradicate the plant, but there are no regulations forcing you to do so.

You would be breaking the law if you:

  • Caused the Japanese knotweed on your property to spread into the wild. This would contravene the Wildlife & Countryside Act 1981 (as amended). This could include allowing the plant to spread from your property into the neighbouring land by its rhizomes extending underground into the adjacent land. It is accepted that the distance Japanese Knotweed can spread underground is a maximum of 7m.
  • Dug up or cut down and then removed the plant from your property. In so doing, the material becomes classed as a waste and would need to be taken to a licensed landfill site with the facilities to deal with it, this can be expensive! If you disposed of it elsewhere, you would have contravened the Environmental Protection Act 1990.

When growing adjacent to built structures such as walls and buildings, the rhizome can damage structures exploiting cracks and weaknesses as the rhizome system expands. As with other plants, the pressure exerted by the expanding rhizome (or roots) can split structures along weak points and push up through car parks and drives where the asphalt has been poorly laid. Japanese knotweed rhizomes in their search for moisture can interfere with drainage pipes and other structures, blocking and sometimes lifting the pipework and clogging sumps. Other underground infrastructures are at risk, such as cabling and water pipes.

Along with other features such as damp and structural defects, surveyors will take the risk of damage from Japanese knotweed rhizome into account in their assessment of a property. This is based on criteria advised by the Royal Institution of Chartered Surveyors.

Where Japanese knotweed is considered to pose a risk to the property, it is usually necessary to undertake to eradicate the plant by implementing a Japanese knotweed management plan. In order to meet the requirements of the mortgage lender the plan and its execution need to be undertaken by a member of a recognised trade association such as the Property Care Association. The mortgage lenders recognise the standards and professionalism of such a trade association along with the assurance that comes with their work.

Typically, a plan will be produced for your approval with costs provided. This will then be carried out, usually by applying herbicide once or twice in the first year and then once each following year until the plant no longer reappears. The property will be monitored for regrowth for the following two years and if still no regrowth, the property will be declared free of Japanese knotweed. Were it to reappear, the herbicide treatment would resume and so on.

In some cases, lenders have simply rejected applications for a mortgage, unprepared to accept a Japanese knotweed management plan. The herbicide used is most likely to be Glyphosate and the application can only be undertaken by an appropriately certificated operative. Glyphosate has a remarkably low toxicity to humans and other animals and it becomes inactivated, effectively harmless, on contact with soil.

Teaming up with your neighbours

A problem shared is a problem halved.

Dealing with the problem of Japanese knotweed on next door’s land

A common occurrence is where the Japanese knotweed on your property extends into the next door neighbour’s plot or your property is free of the weed but it is within 7m of a boundary on adjacent land. A collaborative approach is by far the best way to deal with the matter and any costs to be shared. In some instances, Japanese knotweed can have been introduced to or spread along a number of properties. Achieving collaboration in such a case is more challenging and it would be advisable to take expert advice from the Japanese knotweed specialist. Once agreement has been reached, a plan drawn up and costs agreed, a solicitor should be employed to arrange a contract between all parties. It only takes one property owner to pull out and all the other properties are then put at risk.


Learn how to recognise Japanese knotweed

How to avoid problems with Japanese knotweed and keep it out!

Minimise the risk of your property being invaded.
Most properties do not have Japanese knotweed growing on them.
Simple measures to take to ensure it stays that way are:

  • check that any soil brought onto your property is guaranteed to be Japanese knotweed free.
  • ensure that tools, machinery and other equipment brought onto your property is clean and free from fragments of rhizome.
  • clean soil and plant debris from outdoor footwear and vehicles after being out and about.

These are all sound biosecurity measures that would also avoid introducing other weeds and plant diseases.

Community Protection Notices

Local councils and the police have the power to issue Community Protection Notices against “individuals who are acting unreasonably and who persistently or continually act in a way that has a detrimental effect on the quality of life of those in the locality” including for invasive non-native species like Japanese knotweed. “This means if an individual or organisation is not controlling Japanese knotweed or other invasive plants and could be reasonably expected to do so, the notice could be used after a mandatory written warning has been served beforehand to get them to stop the anti-social behaviour”.

A notice could require an individual or organisation to make reasonable efforts to make good the problems arising as a result of Japanese knotweed within a specified period of time and/or a requirement to take reasonable steps to prevent future occurrence of the problem. Breach of any requirement of a Community Protection Notice, without reasonable excuse, would be a criminal offence, subject to a fixed penalty notice (which attracts a penalty of £100) or prosecution. On summary conviction, an individual would be liable to a level 4 fine. An organisation, such as a company, is liable to a fine not exceeding £20,000.

Call the experts…
Professional advice is available but choose wisely

Consulting and contracting an expert
In order to ensure that Japanese knotweed on your land is effectively and completely treated, you need to obtain professional advice. This can range from checking that you have correctly identified the plant as Japanese knotweed through to drawing up and implementing a Japanese knotweed management plan.

In order to ensure that the advice and management you contract is reliable and recognised by mortgage lenders and other relevant agencies, you should contact a company which is a member of the Invasive Weed Control Group of the Property Care Association.

The service provided should include:

  • A site assessment, in person, by an expert.
  • A follow up report which would usually be a Japanese knotweed management plan.
  • The plan should include consideration of the options for control and an explanation as to how the recommended action was arrived at.
  • The plan should include or be accompanied by an estimate of costs.
  • If relevant you should be offered an appropriate warranty for the work that is proposed.
  • If you are prepared to accept the Japanese knotweed management plan and associated costs, you should be presented with a contract to agree the works with the Japanese knotweed specialist.

Some “do’s and don’ts”

  • Do make a start straightaway to deal with Japanese knotweed growing on your property. The longer you leave dealing with it, the more Japanese knotweed there will be to deal with! Don’t just cut the plant down and try to cover it up. Apart from being highly irresponsible, the problem could come back to haunt you when the plant regrows. If you have sold the house, there could be a legal claim against you.
  • Don’t cut down and/or dig up the plant and put it in the local authority compost collection. This would be breaking the law and Japanese knotweed rhizome is not necessarily killed by the composting process, part of which is to break up the material into small fragments, thereby potentially exacerbating the risk of spread.
  • Don’t contact the Environment Agency, SEPA, Natural Resources Wales or the Northern Ireland Environment Agency to provide advice on your specific situation or to recommend a suitable contractor. They are not able to advise on each and every case and are restricted from recommending contractors.