Tree peonies are hardy, long-lived plants that will flower for decades if given proper care. Tree peonies are generally planted in the fall, as this allows for the roots to develop in plenty of time for spring. It can take several years for a newly planted tree peony to become established, and it is important to be patient as the plant begins to grow. The best time to prune a tree peony is in February.
Consider the shape that you want for your tree peony before you begin pruning. Make a plan for what you want to remove to avoid over-pruning the plant.
Remove dead, diseased or weak branches, cutting back to a live bud or ground level. Allow five to eight stems to remain, depending on the size and health of your plant.
Prune any lateral growth that is causing crowding in the plant or is altering its shape. Tree peonies should be broad and able to support themselves well.
Cut and remove growth of rootstock--shoots that are growing near the main plant which spring from the peony's root system--just below the soil level.
Thin out flower buds in the spring to promote larger and healthier blooms. Two buds per twig are enough to reduce crowding on your tree peony.
Remove any buds that begin growing at the base of the tree peony's stem.
For young plants that appear weak, remove flower buds as they reach the size of a marble. This will promote better blooms as the tree peony matures. Tree peonies generally need very little shaping.
Avoid pruning your tree peony during the first year after it has been planted. Be careful never to prune more than one-third of the total plant at a time.