Sun-loving peonies (Paeonia) come in two main types: herbaceous and woody or tree type (Paeonia suffriticosa). This article will focus on the herbaceous cultivars that are so popular with gardeners.
Herbaceous peonies are native to North America, Asia, and southern Europe, and include about 30 species. They die back in the fall, then emerge again in the early spring (depending on your region). Most are hardy from Zones 8 to 2, with a few exceptions. (If you are buying stock, be sure to check that it isn't one of the exceptions for your region.) In order to bloom profusely, peonies must have a long period of winter chilling while they lie dormant; they do not flourish in the warmer zones. While they do need the cold weather, if you live in areas that receive little snow and have long periods of very low temperatures (20F/-28C), you will need to protect the crowns with leaves or evergreen boughs.
In early spring (March here in Zones 5/6), the dark pink buds will just be peeking through the old growth at ground level. This is an especially important time to see that these tender shoots are protected from snap freezes. If mid-20s temperatures are predicted, I usually add some extra leaves over the crowns, just in case. Once the shoots have emerged and are forming leaves, the frigid temperatures don't seem to bother them.
When the shoots have reached about 3 inches, you'll need to put some supports around the plants. Peonies grow very fast and, if you wait, you'll have a difficult time threading the branches through the supports. Peonies grow from about 2 to 4 feet tall, and the blossoms--especially doubles--are very heavy. Without support, your beautiful flowers will droop to the ground, or be knocked down by wind and rain. Commercial peony hoops are too short to be of much good by themselves. I use the short ones early in the spring, guiding the branches to grow through the squares. Then I add taller supports around the perimeter. Bamboo stakes work well. You can thread green garden twine back and forth, forming a webbing that will hold the flowers erect.
For most of the cultivars, bloom begins in late spring to early summer; unfortunately, the show only lasts about one week--sometimes less if a heavy rain comes through. Peony blooms hold up well as cut flowers, and nothing is quite as elegant as a crystal bowl with pale pink or wine-red peony blossoms floating on water. Once the blooms are finished, cut back the stems to deep within the foliage. Peony leaves are lovely on their own and, as long as they have adequate moisture and sun, they'll provide a nice contrast in to rest of the garden. If allowed to severely dry out, however, they'll turn brown and curl, in which case, you'll want to cut them back.
The Chinese peony (Paeonia lactiflora) is the most popular of the cultivars, with its magnificent doubling habit that resembles nothing less than layers of ruffled organza. Peony colors are widely varied and consist of any shade or hue except blue. Fragrance seems to be tied into type and color: double flowers are more fragrant, as are pinks compared to reds.
Sun, well-drained soil, and good hygiene are all that are needed to grow beautiful peonies. These hardy perennials actually do well in clay soil, since it is more fertile than sandy soil. Peonies are heavy feeders and those planted in less than optimum soil should be dressed with compost or well-rotted manure in the fall, to encourage strong budding.
September and October are the perfect time to plant new peonies. When locating a new peony, be sure the spot is sunny, very well drained, and the planting hole is at least three feet wide. Do not plant peonies near trees with long-reaching roots. Be sure you've chosen the spot where you really want the peony to stay--they do not take kindly to being moved once they've settled in.
Set bare root stock into the planting hole so that the pink "eyes" are no more than 1-2 inches below surface level. If you plant peonies too deep, they will either not flower or they'll produce only one or two very small blossoms. Peonies are fairly drought resistant, but should be watered well through the first season, or during extremely hot, dry weather. (This is when the leaves will die and look terrible.)
In the fall, cut back the dead foliage to about 3 inches, then apply the compost dressing around the perimeter of the crown, being sure to keep it off the crown itself. Remove all cut foliage and destroy it--do not add it to compost piles, as it can be harboring fungal organisms that will infect your entire pile. As winter approaches, if temperatures will be very cold, add the leaves or evergreen boughs to your peony crowns and wish them a pleasant winter nap.
Bud Blast: flower buds emerge in the spring, but stay tiny, eventually turning brown and dying. This usually occurs in newly planted peonies, especially those from divisions. Once the plant matures, the problem disappears. Other causes can be poor soil fertility, cold injury from an extreme winter, too much shade, or a prolonged dry spell.
Botrytis Blight: stems suddenly wilt, turn brown, and dry up. This fungal infection can affect a large clump of stems in a mature plant, or an entire young plant. Remove all wilted stems below the affected area. Do not allow any diseased material to touch the rest of the plant. Disinfect your shears with bleach or rubbing alcohol. If your peony bushes do not have good air circulation, you'll need to consider thinning surrounding foliage, or relocating the peony. Botrytis blight can be prevented by good fall hygiene and careful planting practices.
No Blooms: peonies that have always performed well seem to lose vigor and stop blooming. Peonies are long-lived perennials as long as their growing conditions remain suitable. Plants that have been in the same spot for years may need soil amendments to boost productivity. Another cause of no blooms can be the encroachment of shade trees and shrubs that keep the sun from the peonies. If this is the case, you might want to divide the peonies or move them, but be prepared to wait a while as they reestablish themselves in a new location. Divide the root clumps in late summer or early fall. Using a sharp knife, cut sections that have at least 4-5 eyes (little buds on the roots), then replant as quickly as possible.
Peonies secrete a sweet nectar that is irresistible to ants and other nectar-loving insects. If ants are crawling all over your peonies, do not worry. They do no harm and, contrary to folklore, the ants' presences does not speed up the blooming process. Do not use insecticides to get rid of the ants--you'll only destroy other more beneficial insects in the process. If you cut peonies for use in the house, you might want to swish the blossoms through some water and shake off the ants before taking the flowers inside.
Look at your gardens and see if there isn't a special place for some peonies. You'll be glad you did.
(Editor's Note: This article was originally published on May 4, 2009. Your comments are welcome, but please be aware that authors of previously published articles may not be able to promptly respond to new questions or comments.)