Peonies are typically grown outdoors, but can make good container plants and placed indoors. Peonies are best planted as tubers or small plants in the fall so they can become established during the winter months. However, they can also be planted in the spring, if necessary. When buying peonies, consider that some grow so large they need support and in general, tree peonies have smaller root systems so they might be easier to grow in containers.
Choose a container with drainage holes that can accommodate the peony's roots, and has room to double or triple in size. The container should be heavy (e.g., clay) so that it won't tip over as the peony gets larger and larger. If you plan to place the peony outdoors during the summer, select a light cover container so it doesn't heat up in the sun too much.
Fill the pot about 2/3 of the way with potting soil that is also mixed with plant fertilizer. Then dig a hole that is large enough to for the roots to fit. Plant the eyes---where the plant sprouts from the underground root stem---2 inches beneath the soil.
Backfill the soil around the root and water the plant until the water comes out the drainage holes on the bottom of the planting pot. Always dump the drained water out so the container is not sitting in water. Continue to water the peony in the same manner when the top 1 to 2 inches of soil dries out.
Place the container in near freezing conditions (e.g., unheated garage or attic) from late fall until late winter. Peonies need a cold dormancy to thrive. During this time, water only when the soil dries out completely (test with finger).