Excerpted from 'Herbaceous Peonies: the Perfect Prairie Garden Perennial', previously published in Kinnikinnick, Autumn 2003, Vol 18 No 3.

Peonies are long-lived plants and will tolerate less-than-ideal conditions, but they will perform best if their site is carefully chosen and prepared. Herbaceous peonies prefer heavy, fertile soil and lots of sun, while tree peonies will benefit from some light shade during the hottest period of the day. All peonies require excellent surface drainage, since standing water can cause crown rot to kill the plant. The planting hole should be about 2 feet deep and 2 feet wide, and amended with well aged compost if your soil needs improving. Peonies should be spaced about 3 to 4 feet apart. Herbaceous peonies should be planted so that the eyes on the crown are no deeper than 2 inches. (More than 2 inches, and the plant won't get cold enough in winter to allow flowering.)

Watering is not required by established plants, but newly planted peonies will benefit from supplemental water. Peonies should be fertilized sparingly in spring, with 1/2/1 (N/P/K), or well-aged steer manure or compost around the margins of the plant. If a plant is an older, weak stemmed variety, use a wire cage or peony ring to support the whole plant. After flowering, spent blooms can be removed if desired, but keep in mind that singles and semidoubles often produce decorative seedheads. Do not remove the foliage; it’s needed to build up food reserves for next year’s early growth and flowering. At end of summer, soon after the first frost, prune the foliage (to 1” for herbaceous peonies, 4” for intersectionals) and discard (don’t compost). This is done to prevent botrytis and other fungal problems which can overwinter in dead foliage.

Herbaceous peonies (including intersectional hybrids and herbaceous species) are generally propagated by root division; division is also usually necessary when moving a mature peony plant, or to rejuvenate a very old plant which has stopped blooming at the centre of the plant. To divide a peony root, dig the plant up in early September, wash off the soil, and let it rest in the shade for a couple of hours so that the roots will be less brittle and easier to cut. Cut the roots into pieces with a shovel blade or sharp knife. Each piece should have at least three and not more than a dozen eyes visible; bigger is not better in this case, since for some cultivars a larger division will grow more slowly and bloom less profusely. Replant as soon as possible so that the roots don’t dry out. Store divisions in slightly damp peat moss if you can’t plant them right away.

Peony root divisions should be replanted in the fall so that they can establish a network of feeder roots before the onset of winter. This is why most specialist nurseries only ship peonies immediately after they are divided in the fall. A good second choice to planting bare roots in the fall is to purchase a potted plant from a local nursery and carefully transplant it without disturbing the root system. Survival rates for ‘bargain’ divisions purchased from garden centres and planted in spring are very low, since the divisions are usually small, are frequently too dry or already sprouting after coming out of cold storage, and must support their growth in their first season mainly from their storage roots.