The effect of Japanese knotweed on property

The invasive plant Japanese knotweed can cause serious problems for those wishing to sell their home.

Japanese knotweed is an invasive plant species which is exceptionally hardy, spreads quickly and can cause property damage.

It spreads via a large underground network of roots, going as deep as ten feet. It can push through concrete and has been listed by the World Conservation Union as one of the most invasive species in the world.

It is illegal to allow it to spread to the wild, where it impacts biodiversity and affects flood management by blocking waterways.

Buying a home with Japanese knotweed

When you receive the Property Information Form TA6 from your sellers, it should tell you whether Japanese knotweed is present.

If it is, you need to be aware that mortgage companies are often reluctant to lend and even if you find one who will, it could make any onward sale difficult if your buyers cannot find a loan.

You would also need to ensure the plant did not spread to a neighbouring property, in which case you could be sued in private nuisance proceedings and required to pay for its removal as well as possible damages and expensive legal costs.

Eradicating Japanese knotweed

To eradicate the plant completely, the roots need to be killed or dug up. The digging option is difficult because of the depth the roots can go and is really only viable for large building companies. Even a tiny piece left behind can quickly regrow out of control.

Treatment with weedkiller involved the application of strong chemicals, which have a risk attached and can be hazardous to the environment. Repeated treatment over several years is often needed.

The biggest study to date into eradicating Japanese knotweed was carried out recently by Swansea University. They found that there was no definite way of killing the plant completely.

They emphasised that companies offering treatment could not accurately say that eradication was guaranteed. Instead, the University suggest that sustained control and management is more realistic.

The cost of employing experts to try to eliminate Japanese knotweed can be prohibitive, running into thousands of pounds for just a few square metres. The expense is not likely to be covered by most home insurance policies.