Japanese Knotweed

What is Japanese Knotweed, what's its impact on property, and how can you treat it?

What is Japanese Knotweed?

Japanese Knotweed (Fallopia japonica) is regarded by the International Union for the Conservation of Nature as one of the world’s top 100 invasive species. It is a rhizomatous plant producing underground stems and or roots and is characterised by its destructive nature and rapid spread and can grow to a height of over two metres.

Where does it originate from?

It originates from Japan’s volcanic mountain ranges, in the 19th Century it was regarded by many as a decorative and ornamental plant.

Where is it found?

It is commonly found alongside roads, wasteland including development sites, rivers and railway lines.

Japanese Knotweed is the most common form of knotweed. Other knotweeds include Giant Knotweed (Fallopia sachalinensis), Knotweed hybrid, (Fallopia x bohemica) and Himalayan Knotweed (Persicaria wallichii).

Why is it such a problem?

It can cause damage to property including drains and pipework, patios, paths and drives, boundary and retaining walls, outbuilding, conservatories and gardens. Treatment programmes are both long and expensive and can last up to three years.

There is potential for regrowth and can lay dormant for up to 20 years.

Its spread is controlled in the UK under the Wildlife and Countryside Act 1981, and waste containing knotweed is covered by the Environmental Protection Act 1990 Part II and must be treated and disposed of by a competent accredited contractor.

What treatments are available?

There are a range of available including:

  • Chemical treatment
  • Relocation and herbicidal programme
  • Reduced dig and herbicidal programme
  • In situ capping
  • On site burial
  • Excavation and removal

Our information paper on Japanese Knotweed and Residential Property explains the background to Japanese Knotweed in the UK, considers how lenders have different policies on dealing with its presence, describes effective treatment , includes an assessment framework.

Appendix C includes identification chart for identifying Japanese Knotweed with photographs and a calendar of the growing season over the year.