Removing 5 yr old decorative grasses
Digging works IF you can get all of the roots.
After digging, cover the area with an old carpet, which will smoother new starts.
After digging, mow to keep the grass under control.
Spray new grass or the large grass clumps in mid March with a herbicide such as Roundup, which should kill all of the grass roots. Then compost for 1 year or place I a "cold" compost pile.