Dear John; This is a surprisingly complex issue. I suggest you prune to please yourself. Among the preferences: 1. Single trunk. Pruned as a standard, the plants can get larger. I have seen 7 ft tall rockii with a single main stem. New basal shoots need to be cut away each spring. 2. 3 stems- This is the main pruning done for display in China. This can give a rounded crown and plenty of flowers. 4. Natural pruning- here only dead of 'worn out' stems get pruned back and the plant produces many new small stems. 5. Shaping- to order 6. Cut to ground. I know many instances where tree peonies are cut to the ground each year, accidentally of by intention. If the plant is heathy it can take this for years. New shoots will all come from underground and can produce flowers on these stems. The plant takes on a weird semi-herbaceous look to it. When and how to prune are added considerations. And all will vary to some extant by your climate. In really cold areas stems can be killed back to some degree every year and still flower. There are also natural difference in sp and cvs. Some are wide -spreading, others more fan shaped and others erect, upright. It is harder to prune a tall upright form to be a ground cover and vice versa so you need to know your cv. This is another area where personal choice is most important. If you know shrub pruning methods in general Tree peonies are no more difficult. Best Jim W. -- Dr. James W. Waddick 8871 NW Brostrom Rd. Kansas City Missouri 64152-2711 USA Ph. 816-746-1949 E-fax 419-781-8594 Zone 5 Record low -23F Summer 100F +