Japanese Knotweed

Question ...

I have been throwing Japanese Knotweed into my compost bin not realising what it was. I have details from the government on how to get rid of the offending plant and its stems, but it is not clear whether it would rot down safely in a compost heap.

Do I have to empty the entire contents of the bin and start over? I am terrified that it will go all over the garden!

Answer ...

Japanese knotweed can re-grow from root fragments just 1cm (1/2") long. Before adding knotweed roots or stems to your compost, you should place them in a black plastic sack for at least six months to rot down completely. Check that it is all rotted before being added to your heap.

However, there is a real risk that you will inadvertently spread the weed around your garden if you use the compost you have made. So be very aware of this. It is not so easy to dispose of the material either as in 1981, The Wildlife &Countryside Act made it illegal to spread Japanese Knotweed by dumping material or soil. Any excavated soil from areas where Japanese Knotweed has established must be disposed of at a licensed landfill site and not reused in further construction or landscaping.

When disposing of contaminated soil it is essential that the landfill operator is made aware of the presence of Japanese Knotweed and that the soil is not used for landscaping or restoration works at the tip site. To ensure safe disposal, contaminated soils must be buried to a depth of at least 5 meters. Section 34 of the Environmental Protection Act 1990 places a duty of care on all waste producers to ensure that any wastes are disposed of safely and that a written description of the wastes, and any specific harmful properties, is provided to the site operator.

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