When I "rescued" a garden last fall after an elderly lady left it, I was stunned to see that she had simply laid down very very heavy plastic all over the grass lawn, then piled tons of beauty mulch on it and planted into that. The roots of all the plants were like you describe...just a flat tangled mess because they couldn't go down thru the plastic. I was amazed anything was still alive after being neglected for months but after I got stuff yanked out and pulled apart and replanted it all grew well. Cages are a good idea. I do this too!