Over 50,000 different cultivars of daylilies (Hemerocallis spp.) exist, all perennials that grow from fleshy, tuberlike roots. They produce green, strappy leaves in a mounding clump and produce tall stems, called scapes, that yield trumpet-shaped flowers that each lasts no more than 24 hours. In fall, maintenance tasks drop off, but depending on geography, daylilies can be planted and divided.
Across the northern United States, the months of September through November bring markedly colder weather and the first fall frosts and freezes. Any sporadic flowering or remontant (naturally reblooming) cultivars cease blooming as the frosts kill blossoms and buds. Little by little the green leaves yellow and turn tan. In the milder southernmost U.S., fall brings a respite from the intense hot summer weather and daylilies grow across early and mid fall with lush foliage. Remontant cultivars bloom in September and October, up until the first frost.
Some gardeners do no maintenance work on daylilies until fall frosts and freezes return. The foliage dries and collapses over the ground and shields the roots from cold. Some gardeners, especially in regions where no protective winter snows occur or winters are rainy, choose to rake away dead foliage. A tidy, cleaned daylily bed is exposed to light and air over winter and fungal diseases and rot aren’t as likely to occur. For added insulation from cold and to prevent heaving from alternating freezes and thaws, a shallow layer of coarse mulch can be placed over the dormant daylilies.
In the northern United States, digging up and transplanting daylilies in fall is a bad idea and causes plant death. However, in the extreme southern U.S., such as in the Southwest or along the Gulf Coast, mid to late fall (October and November) is a good time for planting. The winters here are so mild that the daylily roots continue to grow in the cool soil and establish before spring returns. Keep the newly planted roots evenly moist over that first winter after transplanting.
Three general types of daylilies grow and may affect your approach to fall maintenance. Each cultivar of daylily is either deciduous, semi-evergreen or evergreen, referring to how much foliage persists over the winter months. During fall, deciduous types brown all their leaves and go fully dormant. Semi-evergreen types let about half of their leaves wither, while evergreen types retain green leaves in fall through winter. If winters get too cold, even the semi-evergreen and evergreen types may become fully dormant. Do not cut back daylily leaves in fall that are on plants expected to retain green leaves all winter.