My mother always said to leave tops on plants that grow from bulbs or rhysoms(sic)until they die back and turn brown. All the nutrients in the leaves will go into next years growth. Also, check to see when to divide roots in your area. If you don't like the unsightly look, I saw an article that suggested rolling up leaves and fastening them with a rubberband or piece of twine at ground level. Then you can remove dead material easily after it turns brown. Best Wishes