Can I Compost Japanese knotweed?(From the Garden waste category | 1 comment - join the conversation)
No, definitely do NOT compost Japanese knotweed.
Since the 1981 Wildlife and Countryside Act, it has illegal in the UK to allow Japanese knotweed, Fallopia japonica, to plant knotweed or let it spread into the wild and since the 1990 Environmental Protection Act, it has been classed as a “controlled waste” substance and must be disposed of at licensed landfill sites.
Composting it could cause it to regrow in your garden – a fragment just a few centimetres long (of plant or root) could quickly regrow to be a problem in your garden.