Knotty issues

In the mid-nineteenth century, some horticulturalists thought that Fallopia Japonica, a fast-growing plant with bamboo-like stems, would be an excellent ornamental plant in parks and large gardens.

Since then, millions of households have discovered that Japanese Knotweed (JK) is one of the most problematic plant species in the UK. It has been estimated that 1-2% of all residential properties and development sites are affected, and many more are drawn into the problem simply by being adjacent to an affected site.

There is a common perception that JK can cause significant damage to buildings, although there is surprisingly little research on this. It has distinctive extensive rhizomes (underground structures that resemble roots) which are difficult to kill.  Because it is so challenging to eradicate – requiring multi-year treatment with herbicide or excavation – there are some strict controls.

It an offence to plant JK or cause it to grow in the wild. However,

  • it is not illegal to have JK on private land
  • individuals do not have a legal obligation to remove or control JK on private land, and
  • there is no requirement to report that JK is present on the land.


  • allowing contaminated soil or plant material from any waste transfer to spread into the wild could lead to a fine of up to £5,000 or a prison term of up to two years.
  • affected parties, such as landowners of adjacent properties, might also seek damages if JK is allowed to spread onto their property
  • it is classed as ‘controlled waste’ and as such must be disposed of safely at a licensed landfill site, and
  • it is an offence to deposit, treat, keep or dispose of controlled waste without a licence.

That is why some mortgage lenders have strict no-JK policies. There is a specific question on JK in the Seller’s Property Information Form. This has caused problems for house- sellers and prospective purchasers. Claims for damage caused by JK are usually excluded on buildings insurance policies.

Over the last year, the all-Party House of Commons Science and Technology Committee has conducted an inquiry into Japanese knotweed and the built environment. It has now published a report1 of its investigations with a series of recommendations, including

  • national data collection of the extent and nature of JK
  • targeted research about the actual JK impact on buildings
  • looking at why other countries don’t see JK as such a big issue
  • reviewing the nature and extent of declarations on Property Information Forms
  • asking the Royal Institute of Chartered Surveyors to review its risk assessment framework
  • proposing that mediation is better than litigation for resolving disputes relating to JK between landowners.

The recommendations seem eminently sensible. We need to see what the government, the professional bodies, mortgage lenders and eradication contractors do with them.

But, if you suspect you have a problem with JK, do not just dig it up and throw it in the neighbour’s garden! That could be very costly indeed.

1 Japanese knotweed and the built environment

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