Peonies are perennial flowering plants that grow from hardy root stocks. The best time to plant peonies is after they naturally go dormant, or between around September 1 and the first hard freeze of the year. Peonies have distinct growth stages, which are important both for flower harvesting and for deciding when to plant new root stocks.
Peonies go dormant for the winter during late August. In warmer climates, you can leave peonies in the ground over winter. In bitterly cold climates, however, you may need to dig your peony root stocks up and put them in cold storage for the winter. Your peonies need this dormancy before spring to grow and flower properly.
During initial spring growth, your peony roots may send up a number of shoots. After the second year, try to limit the number of shoots to the healthiest five or six. However, try to avoid pruning your peony during its first year of growth. If your peony looks weak during the first year's growth, remove the buds when they are about 1/4 inch in diameter to encourage green vegetative growth.
Budding & Flowering
When your peony buds will depend somewhat on your growing season. If you are growing peonies for cut flowers, don't plan on harvesting the flowers until the peony is 3 to 4 years old. Begin harvesting your peony in its fourth year. Most peonies produce well for up to 25 years. The precise timing for harvest will depend on the variety of peony. Some need to be harvested when the bud is still firm. Others do better when the bud has softened a bit.