Japanese knotweed – an extremely costly, invasive super-weed

Green property issues – no, not party politics or energy performance but an invasive weed: Japanese knotweed

The weeds are growing in public spaces, gardens and private yards at this time of year – but look out for this invasive, damaging and potentially extremely costly super-weed: Japanese knotweed.

Its existence is relevant for home owners, commercial property owners, developers and land owners generally.  Japanese knotweed came to this country in the Victorian era as an ornamental plant but by its survival qualities and ease with which it spreads, it has become a nasty problem.  It has damaged buildings and road surfaces.  Legislation is in place to try and curb its detrimental impact on us.  Lenders are particularly aware of and against its presence at any property for which it is providing mortgage finance and will seek its removal before agreeing to lend.

The Plant:

The plant was discovered growing on the sides of volcanoes in Japan and east Asia by a 19th Century botanist.  On volcanoes its growth was kept in check by eruptions so it developed a clever evolutionary survival mechanism: survival underground in a dormant state for long periods and the ability to reproduce underground.  The plant is hard to identify unless you know what you are seeking.

In the winter the plant dies back and in the spring it sprouts reddish/green bamboo-like stems which sprout into lush green leaves.  Small cream flowers appear at the end of July/August.  So far, so good.  Perhaps the Victorians were justified in introducing it to our gardens: it’s rather pretty.  The problem is that unlike in its natural original environment, it can grow, in this country, unchecked by volcanic activity. It grows rapidly at a rate of up to 20 centimetres a day (and up to about 3 metres in height in total), can reproduce (by underground roots/stems and not seeds) new plants quickly within 10 days and lie dormant under the soil (down to a depth of up to 3 metres) for long periods up to about 20 years.  This rapid growth and relentless spread and potential for re-growth means that it over powers other vegetation and in addition will grow through tarmac and can cause structural damage to foundations of buildings.

The Law:

There are three applicable elements of legislation and civil litigation claims for private nuisance can be sought by adjoining landowners:

1. Under the Wildlife and Countryside Act 1981 (“WCA”), it a criminal offence to “plant or otherwise cause to grow in the wild” Japanese knotweed.  Under the WCA the landowner has to control the plant but does not need to remove it.  The police are responsible for enforcing this legislation.  Under the WCA there are potentially unlimited fines and/or a prison sentence for up to two years if contaminated soil or plant material from any waste transferred is spread into the wild.

2. Under the Environmental Protection Act 1990 (“EPA”) Japanese knotweed is a “controlled waste” and land owners can be fined if it is not disposed of correctly.  Under the EPA, if Japanese knotweed is removed from a site, only licensed contractors can take it to designated landfill sites.

3. Under the Anti-social Behaviour, Crime and Policing Act 2014 (“ASBO”), it is an offence to allow Japanese knotweed to grow on your property if it is not controlled and as a consequence spreads on to neighbouring land.  By ASBO, a community protection notice could be served and result in fines of up to £2,500.00 for an individual or for companies up to £20,000.00.

4. Third party private nuisance litigation claims can be made.

A recent case went much further than anything before it. In Williams and another v N.R. Infrastructure Limited (02.02.2017, Cardiff County Court), Network Rail were held liable to pay damages to home owners who could not sell their houses because lenders would not grant mortgages on their blighted properties.  Network Rail owned adjoining land on which Japanese knotweed was growing.  There was no evidence of actual damage caused by the Japanese knotweed but the presence of it affected the value of the homes. The mere presence of Japanese knotweed on Network Rail land had a detrimental effect on adjoining land values and as a consequence Network Rail was liable to pay damages to its neighbours.

How do you remove it or treat it?

It is important for developers to treat the problem before construction starts on a development site.  Often on potential development sites, all affected soil will be removed and barriers will be installed beneath the buildings (if relevant).

For existing home owners there are several options but none of which are completely satisfactory:

• Apply chemical weed killer

Chemical weed killers are a common treatment but it can take up to five years of treatment to eradicate the problem (as a consequence of the propensity of Japanese knotweed to re-grow from underground roots)

• Take it out or burn it

This is not particularly effective unless you take out all the soil to a deep depth as the survival ability of Japanese knotweed is very high as seen above.  Also, if a land owner is disposing of that soil they would need to be very careful about the disposal legislation under the EPA.

• Introduce bugs to eat it

There is a biological solution but it is new and not yet tested.  A biological control bug is being released widely in the U.K.  It will spread naturally but it will take a number of years.  How effective it will be to eradicate the problem is unknown.

• Eat it!

If all else fails perhaps you can eat your way out of trouble!  Surprising though it seems, it is edible.  The spring shoots can be cooked and eaten as vegetables like asparagus tips.  It can also be made into wine.  However, it is not recommended as you need to be careful to ensure it has not been treated with pesticides or weed killer and any waste from the cooking would need to be disposed of in accordance with the legislation.  Apart from anything else, you would have to eat an awful lot and it would just grow back next year!

• Bring in professional expert consultants?

There are certain firms that specialise in the assessment, management and removal of Japanese knotweed and can assist with potential lender problems.

• Insurance

As Japanese knotweed is often underground and dormant and therefore unseen, is there any protection against it through insurance?  There is legal indemnity insurance available on purchases of commercial property which covers lending institutions against surveys, treatment and expenses for sites and legal expenses for defending against claims from third parties affected by the spread of Japanese knotweed.



It is a problem and not one to be ignored given the potential penalties and costs.  If you are purchasing a property then you should check the site for any signs of Japanese knotweed both at the property and on adjoining land and seek professional advice.  If you have the problem on your own property already then you should be aware of the issues and obligations on you to treat and deal with it in accordance with the law.

Finally, it is recommended that you check the government website which was last updated in April 2017 for guidance: www.gov.uk/guidance/prevent-japanese-knotweed-from-spreading

Images of Japanese knotweed in summer and winter can be found on the Royal Horticultural Society website


For legal advice about Real Estate and Commercial Property, contact Partner, Liz Brady on 01227 763939 or email efb@furleypage.co.uk