One of the rewards of growing perennials is that plants increase in size over the years. As they grow, however they may outgrow their allocated space, die out in the middle, become weed infested, or maybe you just want more of the plant to spread around the garden or give to friends.
Spring is an ideal time to divide summer and fall flowering perennials, although even spring bloomers can usually be divided successfully after they flower. A couple of exceptions are Peony (fall only) and Bearded Iris (summer or fall).
How to divide your perennials
Once plants show signs of growth in the spring, dig up the whole clump. Using a sharp spade or knife, slice the clump in half. Sometimes there is a natural point where the clump can be easily separated. Once the clump is split in two, you can carry on making smaller clumps as desired. Try to keep the clumps a good size and each piece should have both green above ground shoots and roots below. Replant the clumps at about the same depth they were growing at. Water them in well at planting time and throughout the spring if dry. Enjoy your new look!