Removing wilted perennials is not necessary, but can be helpful

A: Removing spent flowers is not necessary for perennials, but may be useful in some cases. Some perennials such as sage, speedwell, aster, black-eyed Susan, yarrow, coreopsis, tall phlox and coneflower can continue to produce flowers if spent flowers are removed.

For other plants, such as irises and daylilies, it is a good idea to remove spent flowers so that the plants do not spend their energy on producing seeds, but instead use resources to maintain healthy roots and shoots. If the seed pods of some perennials are allowed to develop, they can provide interesting garden features in the fall and winter (indigo, purple milkweed, blackberry lily) and food for birds (switchgrass, evening primrose, purple coneflower).