Summer-flowering day lilies (Hemerocallis spp.) provide blooms for several months. Although each flower lives only a short time, the plants constantly produce new buds and flower stems so a single day lily may stay in flower for two months or longer. Most day lilies grow as perennials in U.S. Department of Agriculture plant hardiness zones 3 through 10. The plants go dormant in fall or early winter. Proper trimming keeps the plants healthy and cleans up the garden bed for the dormant season.
Remove individual stalks throughout summer as they finish flowering and producing new buds. Cut down the remaining flower stalks after all the flowers have finished blooming in fall. Cut near the base of the stalk using clean shears.
Pull or trim off dead leaves as soon as they yellow and turn brown, removing them completely from the plant. Some day lily leaves may remain green into late fall, depending on the variety and local temperatures.
Prune back the remaining green leaves to within 4 inches of the ground in mid to late fall. Remove and dispose of all the pruned foliage so it doesn't harbor insects or diseases over winter.
Cover the bed with 1 to 2 inches of mulch after you prune the plants for winter. Stop watering and feeding the day lilies so they go dormant, then resume regular watering in spring when growth resumes.
Things You Will Need
You can remove dead or damaged foliage at any time during the summer, but only cut back plants entirely in fall after they begin to go dormant.