Direct Line magazine

What's Japanese knotweed and how do you defeat it?

Updated on: 10 December 2020

Japanese knotweed

What is Japanese knotweed?

Spotted Japanese knotweed in your garden? Stay calm.

Although it can strike fear into the hearts of even the most experienced gardeners, Japanese knotweed is still manageable.

With a network of special roots called rhizomes, which extend up to seven metres from the parent plant, Japanese knotweed can grow in any type of soil and regenerates from the smallest fragment. Having it in your garden can even cause structural damage and devalue your home.

When the plant was introduced to the UK in the 1800s, Victorian gardeners were enamoured and William Robinson, one of the most influential garden writers of the time, recommended it be planted in groups of two or three.

It’s understandable; Japanese knotweed’s heart-shaped green leaves and clusters of tiny cream flowers aren't unpleasant to look at, but away from its natural ecosystem, it’s extremely difficult to control and can choke other plants.

What are the best ways to tackle Japanese knotweed?

  • Have a plan and stick to it. Eradicating Japanese knotweed will take several years, but it can spread rapidly so leaving it isn't an option.

  • Pull the living stems of the plant out by hand, or cut them cleanly. If you do this every year, you will kill it eventually.

  • Place the stems on plastic sheeting away from soil and allow them to decompose completely before composting. Alternatively, leave them on a plastic sheet to dry out and then burn them.

  • If the clump is not near water, spray it with a weedkiller like glyphosate. Follow the manufacturer’s instructions carefully.

  • If you don't fancy tackling the weed yourself, call in a professional eradication expert.

What not to do

  • Don’t dig or move soil within seven metres of Japanese knotweed — it could contain pieces of rhizome.

  • Don’t shred, chip or strim it – each tiny fragment can regenerate.

  • Don’t try to dig it up – this will only increase its strength.

  • Don’t place any part of the plant in your compost bin/green waste bins — Japanese knotweed is classified as controlled waste and can only be disposed of at specially licensed sites.

  • Don’t dump it – the fragments will re-grow and it’s illegal to spread Japanese knotweed.

Want to learn more about Japanese knotweed?

Check out the Environment Agency’s advice on the matter.

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