The plastic really should prolong 5 to 10 feet outside the boundary space of the knotweed growth. Use rocks or other heavy materials to weigh down the tarps, so they don't shift or blow absent. As this covering will need to remain set up for many years, disguise it with https://japaneseknotweedcontrol65318.activablog.com/37109454/the-basic-principles-of-japanese-control