In the US, the tree peony is hardy from zone 4 to 9. The fall is the best time to plant a tree peony. New roots develop and grow rapidly in 77 to 64 degrees temperature before dormancy in winter. When the temperature goes below 40 degrees, the plant stops growing. In early spring as soon as the temperature is above 40, it starts to grow again. Cover with remay for warmth to encourage quick rooting before dormancy.
Tree peony likes dry and cool weather. It does not require a long period of extreme cold in order for it to bloom in the spring. A period of 30 to 45 days of 32 to 41 degree temperature is enough to insure tree peonies to bloom. In the southern US states where there is heavy rain fall and the temperature often reaches above 90 degrees during the summer, they will be able to grow and bloom in the spring, provided they are planted in a location with good drainage, sufficient ventilation, and under semi-shade. You might consider a covered hoop to help keep them dry and warmish initially.
Storing bare-root tree peony
If your tree peony comes in bare-root form it should be planted as soon as possible upon arrival. However, if you need to store it for a few days, it should be kept cool and moist in a moisture retaining pack such as sawdust or peat moss. Remember the tree peony is a hardy plant.
Selecting a site
Tree peony can be planted under full sun or part sun. It requires at least 4 to 5 hours of sun light daily. In areas where it is very hot in the spring, during the blooming season, the heat causes the flowers to wilt and drop fast. In this case, it is better to plant it in a semi-shady area. Good drainage is essential. In a lowland during the summer where accumulated rain water can cause root rot, it may be fatal. However, you can provide better drainage by planting it on a gentle slope or in a raised bed. Avoid planting tree peonies near large trees which may draw the necessary nutrients away from the peonies.
Preparing the soil
Chinese tree peony likes loamy soil with high humus content to a depth of at least 2 feet. It grows best in soil with a ph of 6.5 to 7.5.
Here are some pictures of peonies that we have grown -