Day lilies have flowers that bloom for only one day and then wither and die, hence the name. Fortunately, each plant has numerous buds and therefore a clump of day lilies will bloom throughout the summer months. Day lilies are self-propagating and when the garden becomes overcrowded and the plants bloom less than they did the previous year, then it's time to separate them. Division is usually only necessary every three to five years. Replant the divisions as soon as possible.
Wait to dig up day lilies in the early spring or in the fall when the plants are finished blooming.
Cut the foliage back to about 6 inches with a pair of sharp clippers.
Dig up the plants. Get up as much of the roots as possible, which begin about an inch beneath the soil.
Pull the foliage apart gently so you can better see the natural divisions of the plant.
Lay the clump of day lilies down and use a utility knife to cut the plant into sections. Each section should contain two or three stems (foliage).
Replant each section in full sun or partial shade. The crown (where the stems meet the roots) should be 1 inch beneath the soil. The hole should accommodate the length of the roots and they should fan out slightly. Space day lilies about 12 inches apart from one another.
Water the plants well--about 1 inch of water will suffice. If it is the fall, also spread about 2 or 3 inches of mulch, such as straw or bark, for winter protection.