Posted: 31/07/2014 at 09:10
A couple of years ago I took over a garden similarly afflicted... It is an amazingly resilient plant. It self-seeds very readily, and I once tried to dig up a plant completely, the tap root went down over 2 feet. The roots are very brittle, you can hear them "pop" when you try to pull up the plants, and they happily regrow from root fragments. I was at first reluctant, but judicious use of a glyphoste squirter on new leaves will eventually get on top. Good luck!