The roots of tree peony shrubs are remarkably cold hardy. They can survive winter temperatures below -20F, so that these shrubs will grow as far north as Canada (zone 3). Because they require some cold for a dormant period, tree peonies grow only as far south as Georgia and mid-Texas (zone 8).
Because tree peonies are long-lived, choose a site where they can grow undisturbed for a long time. They like several hours of sun a day, preferably in early morning and then in late afternoon. The hot, bright midday sun often fades the color of the blossoms. It is wise to place tree peonies where they are somewhat protected from strong wind, and several yards from large trees. Be sure that they are not closer than 3 feet from a wall. They like soil that is well-drained and slightly alkaline to slightly acid (pH 6.0 to 8.0). Plant in early fall so that the root system has plenty of time to develop before the ground freezes.
Purchase 1 to 2 foot tall tree peonies that are container grown. Keep the shrub moist until planting time. Remove it from its container, taking care to keep the soil packed around the root system. Spread any protruding matted, tangled roots, clipping any that have begun to coil around the base of the rootball in the container. Dig a hole wide enough to comfortably accomodate the rootball and deep enough so that the top of the rootball is level with the soil surface. Fill the hole with soil, watering periodically to assure that the soil fills in around the roots. Do not tamp the ground hard around the shrub stem.
If you purchase your containerized tree peony in the spring, leave it in the container until early fall and then plant it into the ground.
Sometimes tree peonies arrive from the nursery bare rooted. Then the graft, the place where the specific peony variety has been joined to a hardier root stock, is visible. Plant these in the fall. Be extremely careful that the graft is at least 5 inches below the soil surface after the soil is firmed over the root system. Spread a layer of mulch on the soil under the shrub and do not allow turf grass to grow near the stem. (See below). While tree peonies newly transplanted in the fall may bloom the following spring, it is not unusual for them to delay a year. Though they may take a year or two to get into the swing of things, tree peonies eventually perform handsomely.
Amendments In Planting or Transplanting
There are a number of products at the garden center that will help your newly planted or transplanted plants deal better with the stress inherent in the planting process. All healthy plants have beneficial fungi, called mycorrhizal fungi, living on their roots. You can buy these valuable additions to your plant’s ecosystem. See the file describing Using Micorrhizae When Planting.
In addition, there are a number of products such as seaweed, compost tea, and beneficial soil microbes that when added to the planting process will help your newly established plants get going faster. See the file New Technology In Plant Growth Activators
For more information see the file on Planting Shrubs. For planting tools see Hand Tools For Digging and Planting in Yardener’s Tool Shed.
Propagation - Unlike many other perennials and shrubs, tree peonies are not easily replicated by division or stem cuttings. It is best to acquire new plants by ordering stock from a nursery.