Just wait. Pruning either of these semi-hardy perennials early in the spring could cause them to wake too early and then die later in the spring. Later in the month of May after you see signs of new sprouts on the plants you can shorten them by two-thirds of their height to encourage more bushy new growth. Sometimes it is not pruning that kills them off but a cold winter. If you do not see any signs of new growth by mid June you can blame the weather and start with new plants. Keep growing, Marianne Binetti