I have chopped down blackberry canes into fairly small pieces in my back yard, The area is a fair size. Can I leave them on the ground, or can these pieces of cane resprout. I'm not interested in using any kind of chemicals. If I dig up the roots, is it possible to smother the blackberries by covering them with heavy black plastic? Or is that a waste of time. I realize blackberries are very difficult to remove.