What is Japanese knotweed?

Japanese knotweed (Fallopia japonica)

Japanese knotweed is a fast-growing, invasive weed. It is relatively attractive to the eye and especially attractive to insects. Japanese knotweed can remain dormant for over twenty years, but once it begins to grow, it can spread at a length of 1.2 m per month. It develops a series of underground roots and shoots, referred to as rhizomes, which can grow out for several metres from the original stand. It is characteristic by its hollow, purple stems and heart-shaped leaves. If you need more information on this, we have a page dedicated to helping our clients to identify Japanese knotweed.Japanese knotweed

As you’ve probably guessed, Japanese knotweed originates from Far East Asia. It was taken from its original habitat on the side of volcanoes by the Victorians and brought back to the UK for ornamental purposes. As a non-native plant, Japanese knotweed has no natural enemies in the UK and has, therefore, become out of control. Native Japanese insects have safely been released into the UK in recent years to try and control the outbreaks, but these insects can only keep a small proportion of the Knotweed at bay. In fact, Japanese knotweed is so prolific in the UK, that Defra estimates that national eradication programme would cost £1.56 billion.

As mentioned, Japanese knotweed is incredibly invasive. It can break through drains, stone paving, tarmac, concrete foundations, boundary and retaining walls and ruin gardens. For these reasons, it can cause issues when looking to buy, sell or re-mortgage your house. It is hard to control without professional help and DIY Japanese knotweed removal is not recommended.

Unlike most plants, Japanese knotweed does not spread through normal germination methods outside of its native Asia. In the UK, it is spread by:

  • The use of soil contaminated by Japanese knotweed rhizomes. A rhizome the size of a fingernail can grow into a new plant.
  • The illegal fly-tipping or irresponsible disposable of Japanese knotweed cuttings. Japanese knotweed is considered ‘controlled waste’ and must be disposed of at licensed landfill sites.
  • If the parent plant is near to water, pieces of the plant can be taken off by running water and spread downstream to other knotweed free areas.

There are many laws and legislation surrounding Japanese knotweed. For example, did you know that by ripping out a Japanese knotweed stem and disposing of it in your garden waste bin, you are opening yourself up to fines and even a prison sentence? This is because there are strict laws prohibiting anyone to plant or otherwise cause to Japanese knotweed to grow in the wild. Read more about Japanese knotweed and the law.

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