Japanese knotweed... just how bad is it?

Misconceptions about Japanese knotweed, the threat that it poses to buildings and how it can negatively affect the value of a property have been challenged in a recent Guidance document published by the Royal Institute of Chartered Surveyors (RICS).

So what is Japanese knotweed?

Japanese knotweed is a hardy bamboo-like perennial plant that grows quickly and strongly. It spreads through its underground rhizomes or shoots, and thick clumps or stands can quickly grow to a height of over 2m during the spring and summer.

It was introduced into the UK in the mid-19th century, it was initially popular with landscapers because of its ability to grow quickly and form dense screens. However, it soon became a problem due to its propensity to spread and establish easily.

Its biological and physiological characteristics have allowed it to take advantage of human interference, ground disturbance and the movement of ‘contaminated’ soil. Its ability to out-compete native plant life, lack of natural predators and ignorance on the part of landowners has resulted in its widespread distribution to all parts of the UK, Europe and North America.

How does it cause damage to properties?

It doesn't, there have been false stories fuelled by the media of Knotweed breaking through concrete floors and causing walls to fall down. Like all plants Knotweed has roots that seek out moisture and if your drainage or foundations are cracked or compromised then the plant can cause further damage ( see our recent blog on drain maintenance ). In fact, the new guidance focuses on how knotweed can affect the way in which you use a property, not how close it is to a building as in previous guidance. It can have a negative  effect on your home's value if left untreated.

Should you be worried?

Knotweed can be managed, if you find knotweed at your property your first step is to contact an expert and get advice on putting a management plan in place. I attended a RICS Knotweed training event a few years ago. The guest speaker was Dr Paul Beckett,  a world leader in Knotweed identification and treatment. His company Phlorum actually offers a free identification service where you can upload images of any plant that you suspect is Japanese Knotweed and get confirmation and advice on next steps.

What's key is to not ignore the plant if you do find it, it has to be professionally managed, cutting, burning or burying can actually make things worse.

Still have questions about knotweed? Click or scan to install the Planna app and book a video consulation with an expert.