Daylilies (Hemerocallis spp.) are hardy, colorful perennials with a proclivity for spreading rapidly--a boon to gardeners with swaths of ground to cover and a bane for those trying to maintain a more restrained perennial bed. Although each Hemerocallis flower lasts for only one day, the plants produce blossom after blossom, maintaining their floral display throughout the summer months. Daylilies are easily propagated by division, often in spring or fall.
Stella D'Oro and other small daylilies with dense growing habits are popular container plants. Kept well-watered and modestly nourished, and with the seed ponds promptly picked off, these container daylilies should continue blooming throughout the summer. However, root overcrowding can bring the floral display to a halt.
Divide container-grown daylilies every two to three years, in the early spring before blooming begins. Turn the container on its side and remove the soil and daylily plant and roots. Take the opportunity to put some fresh potting mix and compost in the container, then tease apart the daylily root fans. Select the most robust looking fans, about one-half of the total removed root mass, and replant these in the container. The remaining fans may be discarded or placed in other pots for sale, gifts or trade to friends and neighbors or to expand your container daylily display.
The Alabama Cooperative Extension Service advises that daylilies can be divided any time of the year but suggests that late fall or late winter/early spring divisions produce the most satisfactory results. The Arkansas Cooperative Extension Service likewise recommends fall division, when cooler weather will ease the stress of the dividing process on the plant--and on the gardener! Late fall/early winter divisions are ideal for thinning an overgrown patch of daylilies to remove excess specimens, so that the remaining daylily plants will have room to stretch their roots as soon as the spring growing season begins. When dividing in the late fall to thin the existing daylilies, discard the thinned root divisions, as they will not have time to become established before winter.
To propagate daylilies by division, the University of Minnesota Extension Service recommends dividing and transplanting them in early spring (although these are not likely to bloom in their first year of planting) or in late summer immediately after flowering ceases. Propagation divisions can be made every three to four years. Remove the entire clump of daylilies and tease apart individual crowns for transplanting. Replant the remaining portions of the original clump. Cut the leaves of the transplants down to several inches of growth, and plant immediately in containers or another garden location. Water the transplants daily for one week to help them get established, and mulch them with straw or shredded leaves for their first winter.