In the fall, gardeners cut back the stems to 2 inches above the ground after the foliage turns yellow. You can also choose to leave those dying stems on the plant to help provide winter protection for your plant. If you choose to do so, remove those dead stems in early spring to make way for new growth. In the spring, before you divide your plants, prune them to 6 inches above the ground. Doing so will prepare your plant for new growth once its growing season comes. You can also prune any dead or dying limbs, flowers, etc., off your plant at any time. It is essential to use clean and sharp pruning shears when you are handling healthy plants.