Although peonies will generally grow extensively large root systems over a period of years, with the proper care and attention to detail, you can grow peonies in containers successfully. Because of the enclosed environment of a container, proper watering and fertilizing is essential to the continued health and vitality of a container-grown peony. Select a large container to give the peony roots plenty of room and these lovely spring-blooming shrubs will put on a spectacular show from your container garden.
Set the planter in the location where you will grow the peony before you place the potting soil into the container (the container will be heavy after you add the soil). Use a container with a capacity of around 20 gallons, such as a whiskey barrel container. Only use a container with drainage holes.
Add 2 inches of gravel to the bottom of the container and then fill the container approximately half full with potting soil.
Remove the peony plant from its temporary container and carefully transfer it to the planter. Situate the peony so it will grow at the same depth as it was in the nursery pot.
Fill the container with potting soil to cover 1 inch above the buds at the crown of the plant. Gently firm the soil around the peony plant with your hands.
Water the peony immediately after you finish planting it. Water the the peony plant thoroughly when the soil just begins to dry out.
Fertilize the peony plant by mixing the fertilizer with water according to the package recommendations for the size of the peony plant. Carefully pour the fertilizer over the soil after the plant flowers, just before the end of the growing season and again when the peony stems are approximately 3 inches tall in the spring.
Cut off the peony stems just above the soil level with the pruning shears in the fall to prepare the plant for winter. Place 3 to 4 inches of mulch over the top of the soil and wrap burlap around the container to insulate the peony roots from winter temperatures. Remove the burlap the following spring.
Pound the stakes into the potting soil the next spring to support the peony plant. Hammer the stakes approximately 4 inches into the soil at two opposite sides of the container. Use stretchy plant ties to attach the peony stems loosely to the stakes.