Peonies are classic garden plants that can thrive for decades with minimal care when planted in a spot they like, in soil that meets their needs. One of the longest-lived of all garden plants, peonies are sometimes handed down from generation to generation in families. But it is very important to do the initial planting correctly, because peonies can be temperamental about being moved once they are established.
Types of Peonies
By some estimates, there are as many as 33 different species within the genus Paeonia, known collectively as peonies. Most are herbaceous perennials, though a few are woody shrubs. Peonies have tuberous roots that are a combination of thick storage roots and thin roots designed to absorb water and nutrients. Careful handling of these roots is critical to planting or transplanting peonies, as well as dividing plants to propagate them.
Peonies are categorized in many different ways, such as by flower type, or by growth habit. In addition to the familiar garden-variety herbaceous peonies with all their flower variations, there are special types such as fern-leaf peonies (Paeonia tenuifolia), a particularly sensitive and prized species; and tree peonies, which are woody, upright forms. These types have some special planting needs.
Sun and Soil Requirements for Herbaceous Peonies
Peonies need a location that receives at least 6 hours of sun each day and a full day of sun is even better. Without sufficient sunlight, you’re get fewer blooms and smaller flowers, and the plants will have a greater risk of fungal diseases, such as gray mold.
Choose a location that is sheltered from strong winds. And plant your peonies well away from other trees and shrubs, since they don't like to compete for nutrients and water.
Peonies are very adaptable, but ideally, they like a well-drained, slightly acidic soil( 6.5 to 7.0 pH). If you are planting in heavy, clay soil, amending with compost or a soil mix labeled for azaleas and rhododendrons will make it easier for your peony plant to settle in. Since peonies can remain in the same spot for upwards of 70 years, taking the time to prepare the soil before planting is time well spent.
Bloom time for peonies varies from late spring to late summer, depending on variety, but all types are best planted in the fall, about 6 weeks before the ground freezes. This gives the plant time to settle in and establish roots before winter. This is especially true when planting bare root peonies or when transplanting, but even when planting potted peonies, fall planting gives better results than spring planting.
Potted Peonies vs. Bare Roots
Peonies are typically purchased as potted plants in 1/2-gallon or 1-gallon containers at the nursery, or as bare roots, often packaged with peat moss or wood shavings in plastic bags. The peonies offered at plant society sales or plant swaps are very often the tuberous bare roots.
When choosing potted peonies, look for healthy specimens without leaf spots or weak-looking stems. When planting from bare tuberous roots, make sure the root clump has at least 3 to 5 "eyes"—small reddish buds like potato eyes. These eyes will eventually elongate and become the plant's stems. A mature peony should be at least 3 or 4 years old before it is divided into bare roots. Peony eyes start off as small reddish buds, similar to the eyes of potatoes. Tuberous clumps with only 1 or 2 eyes may still grow, but they will take longer to become established plants.
Give each peony plant enough space to grow to maturity without being crowded. That means a 3- to 4-foot diameter for each plant. Peonies are especially prone to gray mold (botrytis) when planted too closely and air cannot flow freely between plants.
Peonies like a good chill in the winter. In order to set their flower buds, peony roots should be planted relatively close to the soil surface—only about 2 to 3 inches deep. It may feel odd to leave roots so exposed, but peonies actually need this chilling to attain dormancy and set buds.
How to Plant Bare Root Peonies
- Dig a hole about 2 feet deep and 2 feet across. The soil should be well-drained and humusy; if necessary, add organic material in the planting hole. If the soil is heavy or very sandy, compost makes a good amendment.
- Add one cup of bonemeal into the soil, since peonies need the phosphorus it provides.
- Mound up the soil in the center of the hole to a height just below the surface level.
- Set the root clump on top of the mound so the eyes face upward, with the roots only about 2 inches below the soil surface.
- Backfill the hole, taking care to bury the roots no more than 2 inches deep. Compress the soil gently.
- Water by thoroughly sprinkling the area; do not flood the planting site.
How to Plant Potted Peonies
- Prepare a fairly large planting hole, amending it with compost and mixing in a cup of bonemeal.
- Remove the peony from its nursery container, and slightly loosen the root ball. Position the plant in the hole at the same height it was in the nursery container.
- Backfill the hole around the plant, compressing the soil firmly.
- Thoroughly water the planting site.
If an established peony needs to be moved, transplanting should be done carefully to avoid disturbing the roots any more than necessary. As with any planting, fall is the best time to move a peony.
- At the new planting site, till up the soil 12 to 18 inches deep, and mix in a 4-inch layer of compost or peat moss.
- Water the peony plant with 1 inch of water one or two days before transplanting. Your peony must be well hydrated before moving it.
- Dig around the root ball of the peony using a sharp spade, getting as much soil as possible.
- Slide a tarp under the root ball to keep it intact, then lift the plant from the ground and carefully carry or slide it to the new location.
- At the new location, dig a hole that is twice as wide as the peony's root ball, and exactly as deep as the root ball.
- Plant the peony at exactly the same depth as it was in its old location. Backfill around the plant. Tamp the soil down with your hands, but do not pack it too tightly.
- Water thoroughly. Add a 3-inch layer of compost or mulch around the base of the plant. This will keep the roots moist and cool while the plant is establishing in its new location.
Peonies are best propagated by lifting and dividing the root clump, and immediately replanting the divided pieces. A peony may require this after about 10 years when it begins to lose its vigor and becomes rootbound. Here, too, fall is the best time for this activity.
- In fall, just before you plan to divide, cut the foliage of the peony back down to ground level.
- Dig up the entire plant and remove as much soil as possible by soaking with a hose
- Using your hands, manipulate the roots into dividable portions, each with 3 to 5 eyes, then use a sharp knife to cut the tuberous root clump into divisions.
- Cut away all the tiny roots on each division, leaving only the large, fleshy roots.
- Replant the divisions as soon as possible, following the instructions above.
Tips for Caring for Peonies
- Feed lightly. An annual application of compost mixed with a very small amount of fertilizer around the base of the plant is all that is needed.
- When you do feed with compost and fertilizer, do it just after the plants have finished blooming.
- Support the flower stems with metal rings or cages to prevent them from breaking.
- Deadhead flowers as soon as they begin to fade, cutting the stems back to strong leaves.
- Cut the foliage to the ground in the fall to prevent overwintering diseases.
- Don’t smother peonies with mulch in winter. In the first winter season, you can mulch loosely with pine needles or shredded bark, but mulch should be promptly removed in spring.
Special Notes for Fern Leaf Peonies
Fern leaf peonies are planted and cared for in a manner similar to standard peonies, but it is especially important to keep them well watered. Feed them each fall before the foliage fades with a mixture of bonemeal and compost. If you use commercial fertilizer, avoid products heavy in nitrogen, because this reduces flower production. In the first year or two, fern leaf peonies may die back in mid-summer immediately after flowering. This is expected and is no cause for concern. Fern leaf peonies take several years to mature and flower, so don't get discouraged. Fern leafs have especially sensitive roots, so use great care when moving or dividing them.
Special Notes for Tree Peonies
Tree peonies like a slightly more alkaline soil than standard herbaceous peonies, and they do not want to compete with other shrubs. And do not cut them back to ground level in the fall.
Tree peonies need iron and phosphate and do well with an annual feeding of sulfate and bone meal in spring. Unlike herbaceous peonies, they need regular feeding with a 5-10-5 fertilizer.