The best time to divide daylilies is in the fall when they are going into dormancy. I suggest dividing daylilies every 3 to 5 years. Dividing daylilies is an easy task and an enjoyable one for those gardeners who like to have their plants multiply. When I divide daylilies I usually trim them back to about 6″ in height. Then I lift them from the ground and divide the crowns. The new divisions can then be replanted.