Well over 50,000 different cultivars of daylily (Hemerocallis spp.) exist, all producing trumpet-like flowers in a variety of forms. Plants are either winter dormant, partially evergreen or evergreen, describing the persistence of leaves across the colder winter months.
Daylilies regarded as semi-evergreen or evergreen retain their green leaves in winter only if the climate isn’t too cold, such as below 20 degree Fahrenheit. While these plant types grow in regions with colder winter temperatures, they may become fully deciduous and dormant in these harsher climates.
While grow slows or halts in winter, evergreen or semi-evergreen daylilies still make food in their green leaves. The leaves or the dried leaf debris acts as an insulating mulch over the crown of the roots, helping prevent any cold damage. If possible, avoid cutting back the foliage when winter frosts may still occur and wait until early spring for pruning.
If evergreen daylily plants look unkempt and sickly in winter, you may selectively remove dried leaves and even the remaining green leaves if aesthetics are important. Don’t expect leaves to regrow until warmth returns in spring. If a cold snap is forecast, consider placing mulch over the plants to protect them from penetrating frost and freezes.