Tree peonies, known botanically as Paeonia suffruiticosa, are woody flowering shrubs that are frost hardy and preserve their branch structure above ground overwinter where herbaceous peonies will not. Like most flowers, tree peonies rely on bees, birds, butterflies and other arthropods and insects to pollinate the flowers when in bloom. Hand pollination can also be done to assist when bee or other agent populations are not present in the garden.
Hand pollinate your tree peonies by picking up the sticky yellow pollen grains from the anthers of mature open peony flowers with the tip of a small, and inexpensive new artist's paintbrush. Paint the pollen grains onto the central stigma of the flower structure to complete pollination.
Import or rent a colony of bees to visit and carry out pollination of your peony plants during their bloom period. Contact an apiary pollination service or a professional bee keeper to assist you each spring and summer as necessary to keep the shrubs producing year after year.
Refrain from spraying or applying insecticides anytime in the spring and summer when your peonies are in bud and bloom as these can kill or, at a minimum, dissuade the visits of, bees and other necessary pollinators.