One of the first, and best known, re-blooming daylilies is the cultivar "Stella de Oro" (Hemerocallis "Stella de Oro"), which is hardy in U.S. Department of Agriculture plant hardiness zones 4 through 11. It first appeared in 1975, and 10 years later won the Stout Silver Medal. This is the highest award a daylily cultivar can receive from the American Hemerocallis Society. Like most daylilies, "Stella de Oro" benefits from division every few years.
How Often Should I Divide?
"Stella de Oro" is a dwarf daylily with foliage that only grows 12 inches tall. It tends to form tidy clumps that work well planted in rows, as individual clumps in perennial borders or massed as a groundcover. As the clumps grow, the individual daylily fans become crowded. Regular division reinvigorates daylilies, and gives you more plants for your garden or to pass along to other gardeners. Divide "Stella de Oro" every two to three years, when you notice a decrease in the number of blooms.
What Time of Year Is Best?
Daylilies are remarkably resilient plants, and can be divided any time during the spring, summer or fall growing seasons. Spring is the best season for division, however, since daylilies are actively growing. You want to divide plants when the new foliage is just starting to grow. This gives the daylilies time to put out new growth before blooming in the summer. Plants that were divided in the early spring will still flower, and may even produce more flowers than plants that were not divided.
If you miss dividing in the early spring, the second best time to divide plants is in the early fall. Daylilies put out another flush of growth after blooming. For "Stella de Oro," this doesn't happen until the weather starts to cool. You might have to cut off some late bloom stalks in order to divide the plants in early fall.
How Do I Divide Daylilies?
If you divide in the late spring, summer or fall, cut back the foliage to 8 inches tall with a pair of hedge shears and remove any flower stalks before dividing. For early spring division, you can skip this step. Make sure you disinfect shears and other cutting tools before use. Do this by soaking the tools in a mixture of 1 part bleach to 3 parts water for at least 5 minutes. Rinse tools in clean water, then let them air dry.
Use a gardening fork to lift the entire daylily clump from the soil. Separate the clump into smaller clumps using the gardening fork or a large, sharp knife. Each fan-shaped plant can grow on its own, but it is best to leave at least four fans together in each clump when you're dividing daylilies.
What Comes After Division?
Before replanting the daylily divisions, amend the soil with 2 to 3 inches of well-rotted compost worked in to a depth of 6 to 8 inches. This will provide a slow-release form of nitrogen and loosen the soil for new roots.
Re-plant each division at the same depth the plant was originally growing and space clumps 18 to 24 inches apart. Water each daylily clump thoroughly, and continue watering enough to keep the soil moist throughout the spring, summer and early fall. "Stella de Oro" needs little supplemental water after this first year.