Once your peony has flowered you may wish to dead-head the blooms. Dead-heading your peony is not essential but it will keep the plant looking tidy and encourage further root growth.
Do not cut back the foliage – even if it is dead looking – until the Autumn because your peony is still growing. Cutting back of herbaceous peonies is easy: simply cut everything back to about 2cm above the ground. Cutting your peony back will assist with good hygiene and help mitigate against any disease the following year.
Tree peonies respond well to pruning. Prune in the Autumn and either take back the top growth by about 1/3 in stages or, if you have a multi-stemmed tree peony, cut back every 3rd stem to about 2cm removing the oldest stems first.