The right cut stage
The optimal cut stage of development of the buds is hard to describe in words. For most varieties the flowers are ready to be harvested when the bud feels 'as soft as a marshmallow'. Feeling the bud is best done by placing your pointing and middle finger underneath the bud, and pressing it gently in the top center with your thumb of the same hand to feel softness (see image on the left).
Flowers of single varieties are ready to be cut a bit sooner in general, so when the bud is still a bit harder. A general rule of thumb is: The more flower petals a flower has, the softer the bud should feel at its right cutstage.
Experience is the very best teacher in this, especially because every variety is so different. The practiced person will discover a minimal change in bud shape and/or color difference/intensity of the bud when it has reached the ideal cut stage.
Too early harvested peony flowers do not open. These prematurely picked flowers are known in Holland among growers as 'drumsticks'... Please also pay close attention to this when you buy peony flowers from a grower, at the market or in the shop!