Japanese knotweed: what you need to know

It's never a good day when you find Japanese knotweed on your property. This large perennial plant has the power to affect your home valuation when you try to sell your house, so it needs to be quickly and effectively treated. Here's what you need to know about this leafy home invader.

What is it?

Japanese knotweed is a bamboo-like plant with white flowers that was first introduced to the UK in 1825. In Japan, the plant is kept under control thanks to indigenous insects, but there's nothing to restrict its growth here in the UK. It can increase in size quite quickly, sometimes over a yard a week. In 1981 the Wildlife and Country Act made it illegal to introduce Japanese knotweed into wild spaces, and if you don't treat the spread of this plant on your own property, you could even be served with an Antisocial Behaviour Order.


Why does it cause problems?

Buildings are no match for Japanese knotweed as it can grow through concrete and weaken your property's structure. Every house therefore needs to go through a proper survey at some point to make sure it's clear of the weed, or else its home valuation may be affected.


If Japanese Knotweed shows up on a homeowners survey the seller will usually have to foot the bill for a specialist report to be commissioned. The report will assess the risk level on the RICS scale and detail how the knotweed can be treated. The two parties will then decide whether or not to go through with the sale and how to go about removing the plant from the property.

How do you get rid of it?

If you find Japanese Knotweed in your home you should never attempt to remove it yourself but instead hire a professional. They will either spray the plant or inject herbicides into the stems. Removing just a small patch of the plant can cost £1,500, so if a large area of your property is affected, you could be looking at a significantly higher sum.

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