I noted recently that cardboard is excellent for suppressing unwanted vegetation and lasts for several months before biodegrading. So I was happy to accept the offer of a pile of boxes from a recent house move. Couch grass is pervasive on the allotments. It would need to be covered at least a year or two to get rid of it but hopefully the cardboard will knock it back a bit. And a good way to "draw" the layout of the paths.