Perennial herbaceous plants are preferred by many gardeners because they come back year after year, eliminating the need to replant every spring. However, to maintain a lush and attractive perennial garden, it is necessary to devote time and energy into dividing perennials every so often. Not all perennial plants require division, but most do and will show signs that it is time to divide, such as fewer blooms or a dead spot in the center of the clump. Ornamental grasses, irises and daylilies are particularly notorious for the latter.