Getting rid of the foliage....which isn't "evergreen" in my climate....gets rid of any borer eggs that might be there, gets rid of a lot of fungal disease spores that overwinter on the leaves, keeps the frozen leaves from becoming a "mulch" on top of the rhizomes, helps to keep tree leaves and trash from "sticking" in the bed, as winter winds blow them around, and, just generally looks better ! If it's NOT done in the fall, it has to be done sometime before new growth starts
