Daylily (Hemerocallis spp.)
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by Dr. Susan Hamilton

Almost everyone loves daylilies (Hemerocallis spp.). They are showy, dependable, easy-care perennials that can fill a variety of garden niches. They make colorful shrub borders and perennial beds and excellent ground covers on slopes. Once established, their roots help prevent erosion. Small cultivars are useful in containers.

Although different varieties of daylilies can bloom from late spring until autumn, individual flowers last only one day. Thus the name. Since each plant produces many buds, the total blooming time of a well-established clump may be 30 to 40 days, and many varieties have more than one flowering period in a season.

Growth Habit
Daylilies range in height from 8 inches to 5 feet. Flower size ranges from 2 inches to 8 inches. They can bloom the year they are planted, but they reach full size in three to four years.

Growing Conditions
Daylilies grow best in direct sun or light shade. Cultivars with dark-colored flowers should be protected from strong afternoon sun, which may fade their petals.

Daylilies prefer slightly acidic (pH 6 to 6.5), well-drained soil with plenty of organic matter. They are, however, very tolerant and will grow in almost any soil with adequate drainage. If drainage is a problem, plant daylilies in raised beds. Although daylilies will tolerate planting during any time of year, the best time to plant them is during the early fall or early spring, when soil temperatures are moderate.

Plant daylilies 18 to 24 inches apart. Set the plant so that the crown (the point where roots and foliage meet) is no deeper than 1 inch below the soil surface. Water plants thoroughly after planting, and continue to deep-soak them at least weekly until established. Although daylilies are drought-tolerant once established, consistent watering while budding and flowering improves the quality of the flowers.

Although daylilies grow adequately without fertilizer, light fertilization is recommended. They prefer moderate nitrogen and higher rates of phosphorous and potash. Slow-release fertilizers are best. Fertilize them in the early spring as new growth appears, and once again in midsummer. Water after applying fertilizer. Mulch helps to conserve moisture in the soil and control weeds. Daylilies can, however, tolerate both drought and flooding and seem immune to heat stress.

Remove spent blooms and seedpods after flowering to improve appearance and encourage reblooming. When all the flowers on a stalk are finished, cut off the stem close to ground level. Remove dead foliage from daylilies as they die back in the fall.

Propagation
Daylilies rapidly form dense clumps. Dividing the clumps is not essential, but will help the plant to continue to produce optimal flowers. It is best to divide plants following flowering, but they will tolerate division throughout the entire growing season.

To divide a clump, lift it out of the soil with a garden fork. Separate the clump into individual fans (sections with a set of roots and leaves) by shaking them to remove as much soil as possible. Next work apart the roots of individual fans.

Problems
Daylilies make relatively carefree additions to the garden; however, thrips, spider mites, aphids, slugs and snails are sometimes uninvited guests. Aphids, which feed on daylily foliage and flower buds, can be a problem during the cool spring. In addition to the tiny insects themselves, cast-off skins (resulting from molting) indicate their presence. A serious infestation can cause foliage damage and mar the appearance of flower buds. There are several sprays available to control these pests. Read labels carefully before applying any pesticide.

A new daylily disease has arrived in Tennessee - daylily rust. Daylilies infected with this fungal disease have leaves that exhibit bright yellow or orange-colored spots with raised pustules. Orange spores emerge from the pustules. As symptoms progress, leaves turn yellow and dry up. The disease is easily spread since viable spores can be carried long distances on plants without the plants showing any symptoms. Other less-threatening daylily leaf diseases can be confused with rust, especially daylily leaf streak, which is common.

For more information about daylily rust visit the Web site http://www.ncf.ca/~ah748/rust.html#rust1. If you diagnose or suspect daylily rust on your plants, remove all infected foliage and bury the clippings. Following foliage removal, sterilize pruning tools with a solution of 70 percent alcohol or 10 percent bleach and wash hands, gloves, or clothes to prevent rust from spreading to other daylilies in the garden.

Because this is a new disease, no fungicides are labeled for use on daylily rust. If you treat newly emerged foliage with a fungicide, be sure the label indicates it can be used on ornamentals in the landscape. Spraying infected foliage is not useful.

Outstanding Selections
Thousands of daylily cultivars exist, so a daylily exists to satisfy just about everyone's taste. Although the only colors originally available were yellow, orange and a brassy red, daylily colors now range from the palest lemon to bright yellow; to scarlet and maroon; and to pale pink, and lavender. Blue is the only color still unavailable in daylily flowers. Near-whites are found among the palest tints of yellow, pink, lavender or melon.

If you'd like to learn more about daylilies or if you want to cultivate an existing passion, consider joining the American Hemerocallis Society (AHS). You can learn more about them at http://www.daylilies.org/daylilies.html

Print-quality photos and the UT Gardens Logo are available. Download them now.

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Dr. Susan Hamilton is an associate professor of ornamental horticulture in the University of Tennessee Department of Plant Sciences and director of the UT Gardens. The UT Gardens are located on Neyland Drive in Knoxville. They are open seven days a week during daylight hours. Various selections of witch hazel are currently in bloom, and if temperatures warm, the pansies and violas should put on a colorful show.