The biggest mistake people make with their peonies is leaving them completely unsupported. If peony flowers are left unsupported, they will collapse to the ground almost as soon as the buds open. Peonies fall over because the stems aren’t strong enough to support the huge peony blooms. The peony stems may be able to handle the weight for a few days while the buds are opening.
But throw a rain shower or two in there and… timber! The peony flowers quickly flop to the ground.