Summarize the following:
Dividing the plants will rejuvenate them and improve blooming. Since daylilies grow so vigorously, they will likely need the additional space to stay healthy, as well. Divide daylilies after they have bloomed, but prior to the first frost. Slice it into 6 to 8 sections (root divisions). Each root division should have several stems on the roots. Lop the foliage back 6 inches and remove any stems that look stunted or unhealthy.  Only choose your healthiest daylilies for division. Cutting back the foliage helps the roots establish themselves more easily when replanted. Dig a 12 ft (370 cm) by 12 ft (370 cm) hole for each division. Put 1 division in each hole and refill the hole with soil. Make sure the crown is 0.5 inches (1.3 cm) below the ground line. Water the new transplants thoroughly.  Make sure that the crown isn't too deep. Replanting that way can cause the crown to rot. The daylilies will grow and fill in the new space around them.

Summary:
Divide daylily plants every 3 to 5 years after initially planting them. Raise the whole daylily plant clump from the earth. Replant the root divisions 24 in (61 cm) to 36 in (91 cm) apart.