Daylilies are an extremely popular perennial. They are fairly low-maintenance and make wonderful plant partners for both ornamental shrubs and perennials in a mixed border. They are adaptable plants, flourishing in hot and cold climates and tolerating drought. Daylilies are overall good performers. Hybridizers are coming out with dazzling cultivars in every size, shape and color you can imagine.
The Latin name, Hemerocallis, means beauty for a day. The individual flowers, as the name suggests, last for only one day. The flowers are positioned on scapes--tall, leafless stalks that rise from several inches to 3 feet above the lush, strap-like foliage. The branched scapes produce from 10 to 50 buds each, ensuring a long flowering season (6 weeks on average).
Depending on the cultivar, flowers appear from late spring into October. They are classified as early (E), middle (M), or late (L) and reblooming (RE), with several variations in between. Rebloomers can be "bud builders" which produce new buds throughout the season, such as the popular 'Stella de Oro', or cultivars that flower once, take a small vacation, and then rebloom later in the season.
Deadheading daylilies is important. Snap the dead flower off at the base of the flower (where it joins the scape). Make sure that you snap off the entire flower (not just the petals); otherwise a seed head will form. If too many seed heads form, the plant's energy will be channeled into seed production, resulting in a weakened plant with poor flowering the following year. Once all of the flowers have bloomed, cut the scape down to the basal foliage (base of the plant).
Some small-flowered cultivars are self-cleaning and require less deadheading. Rebloomers should be deadheaded to encourage repeat flowering and showy, large cultivars should be deadheaded for aesthetic reasons. Some purple or red flowers stain your hands when you deadhead them.
After the plant has flowered, it is common for some of the foliage to start to die back. Either pull the yellowing foliage off by hand or cut with a pair of pruners. If the foliage starts to look too tattered, you can cut the entire plant down to several inches from the ground (4 to 6 inches). The foliage will then rejuvenate within a month. Remember to give the plant supplemental water to encourage the new growth. Don't cut the entire plant back every year because you'll weaken the plant.
Some daylilies are evergreen, some semi-evergreen and others dormant in the winter. Evergreen daylilies are best adapted to warmer climates. In the New York area, most daylilies go dormant. You can either clean up the dead foliage in late fall or wait until early spring.
Most daylilies need to be divided every 4 to 10 years, depending on the vigor of the cultivar. Reblooming daylilies tend to be more vigorous and should be divided every 2 to 3 years. To divide, lift the clump with a fork and shake or wash off excess soil. Divide with a sharp knife or spade. If the clump is very large, try the double-fork method. Make sure that the new divisions have 1 to 4 fans of foliage. The larger the division, the faster it will rebloom. Amend your soil with compost when you replant.
Daylilies are fairly disease and pest resistant, making them good candidates for a low-maintenance garden. They are sometimes attacked by aphids and thrips; neither will kill the plant, but they may disfigure the flowers. The easiest remedy is to spray the plants with water or soapy water.
Daylilies benefit from supplemental water during hot summers. Overhead watering (and rain) may spot the flowers, but since each lasts only a day it won't destroy the beauty of the plant. Daylilies can also suffer from leaf streak, a fungal disease that causes discoloration of the leaves. Simply remove damaged leaves.
The New Encyclopedia of Daylilies by 
Daylilies for the Garden by 
The Color Encyclopedia of Daylilies by 
