Daylilies are perennial plants that grow from rhizomes. Growing horizontally under the ground, long-lasting lily plants will happily spend several years in the same spot producing ever-larger clumps of foliage and flowers. Separating overgrown daylily clumps is known as propagation by division. Daylilies benefit from separation every three to four years.
Symptoms of overgrowth that let you know when daylilies need to be divided are: smaller flowers or less bloom, dead spots in the plant centers, slow growth, small straggly leaf straps. Separating the daylilies gives new plantings for free, with just a bit of effort.
Determining the best season to divide lilies depends on your climate. Some daylilies are evergreen and will grow year-round in warm areas. Consult a hardiness zone map like that found on the US National Arboretum website if you’re unsure about your climate type. Using bloom time as an indicator for separating lilies is another common practice. Allowing the plants to use energy for producing roots instead of flowers ensures healthy new lilies for the following year.
Using the climate as your indicator divide daylilies in the fall if you live in a mild area. The plants will have a chance to put down roots before the strenuous blooming season occurs. Divide in the spring if your climate is harsh in winter. Your new plants will have late spring and early summer to grow before facing winter’s cold.
Using bloom time as your indicator divide spring or summer blooming lilies in fall and those that bloom in summer to early fall in the spring.
Work your fork or spade under the clump all around the lily and lift it gently. Free the daylily clump from the ground and set it on your tarp. Rinse lightly with a hose to get off excess dirt or mulch and expose the rhizomes for cutting.
Look for smaller divisions to bloom the next year. Keep one large division to replant in each spot where a daylily was dug out. Discard any rhizomes that appear rotted. Rinse your tool when separating several lilies to prevent disease. Use a weak bleach solution (1 part bleach to 10 parts water) after the rinse to sanitize your tool before dividing the next lily clump.
Set up a regular watering schedule for the next 4 to 5 weeks. Cover divisions that can’t be put back in the soil right away with damp burlap, keep them moist and out of direct sunlight. Pot up separated daylilies that you don’t want for your friends.
If daylilies have formed large clumps but appear to be doing fine they can be left for up to 6 years without division. Using deciduous daylilies in hard-frost areas is best. Evergreen or semi-evergreen daylilies need protection in harsh winters and are best for milder climates.
Daylilies hybridize freely and will not grow true from seed so the best way to get new plants that will look the same is by division. Daylilies are prone to crown rot caused by frost heave in harsh climates. Always protect lilies with a thick mulch layer.