Why the canal and rail corridors running through St Helens suit knotweed, and what to look for along your own boundary.
Knotweed spreads through fragments of root and stem, and long, thinly managed strips of land suit it. St Helens has several: the Sankey canal and its towpath, the Liverpool to Manchester railway through Rainhill and Newton-le-Willows, and the lines running through the middle of the borough. Wherever those corridors meet back gardens, a stand can arrive without anyone noticing.
Walk the back fence in spring for red-purple shoots, then again in July for tall hollow canes standing above the boundary.
The owner of the land it is growing on. A survey of your side shows whether it has crossed the line, and that record is what you hold if you need to raise it with someone.