How it Spreads
So where did Japanese knotweed come from? How did it get here? Why is it a problem? These are questions that many people have been asking for a long time.
Its rapid spread across the country is remarkable when you consider that it doesn’t form viable seed in Britain, but spreads through bits of the rhizome which become detached from the main root-mass. In fact, all the plants recorded in Britain so far have been female, and any seeds formed are hybrids with another species.
Japanese Knotweed is very common on sites that are disturbed by human activity, like railway lines, old allotments, rubbish tips and derelict land. The main cause of its spread is by transferring loads of soil, rubble and rubbish between sites. It can also spread from site to site through bits of root stuck to machinery and tyres.
It can spread rapidly down watercourses. Floods can easily dislodge rhizomes, which are carried downstream to start new colonies.