Once daylily clumps become too large and flowering decreases, you will want to divide your dalillies. Diving your daylilies rejuvenates them. Check the center of your daylily plant to see if there is any dead growth. If there is, your plant is telling you it’s time to divide it. The best time to divide daylilies is shortly after they have finished flowering in late summer to early fall. You can expect to divide daylilies every 3 or 5 years in order to keep them healthy and blooming strong.