HOW TO GROW PEONIES

Paeonia lactiflora. Photo by: PaylessImages / 123RF.

Zones:

There are garden-worthy peony varieties for Zones 2 to 8.

Types:

There are three types of peonies: herbaceous (bush), tree and Itoh (intersectional). Compare them in detail here: Types of Peonies.

Height/Spread:

Herbaceous and Itoh varieties grow 1 to 3 feet tall, with a similar spread, while a mature tree peony can reach 4 to 7 feet tall and 4 to 5 feet wide.

Exposure:

Most peony plants are sun-lovers. However, tree peonies prefer light shade during the heat of midday, which encourages the blossoms to last 10 to 14 days, rather than fading quickly (two to three days) in full sun. In China, parasols are enlisted to protect the delicate flowers from sun.

Bloom Time:

Peony season begins with shoots and leaves emerging, but the real show is when the flowers bloom in late spring. In most locations, they will bloom in April, May or June. Expect tree peonies to bloom first (around Mother’s Day), followed by herbaceous varieties (around Memorial Day) and then the intersectionals. If you include all three types in the garden—tree, herbaceous, intersectional—you can enjoy blooms for up to seven weeks.

Flower color:

Colors range from white, pink and red to coral, maroon and yellow. Many peony flowers change color as they open, so make sure to check them daily to appreciate these differences.

Fragrance:

Many peony flowers are fragrant. Their scents can differ between cultivars—some are scented sweetly of lemons, some have enticing citrus smells, and some are described as slightly spicy. Words like delicious and confectionary are often used to describe their smell. Decide how strong you want the scent—some are lightly scented, while others have a stronger fragrance. For example, Chinese tree peonies have a stronger fragrance than Japanese tree peonies.

Pests and diseases:

Fortunately, they are deer and rabbit resistant. Unfortunately, they are susceptible to botrytis blight, a fungus that can cause young shoots to rot, unsightly spots on leaves and prevent flower buds from developing. Making sure there's plenty of air circulation around your plants will help prevent fungal diseases. Learn more about issues that can arise in the Missouri Botanical Garden's guide to peony problems.

If planted well, herbaceous peonies will happily send up new shoots each spring for decades. Photo by: gutaper / 123RF.

When to plant:

Plant bareroot peonies in the fall (prior to the first frost) and they'll have the best chance of blooming the following spring. Those planted in spring may not bloom for two years or more.

Where to plant:

Picking the right spot for your peony plant is essential to its success. If sited incorrectly, deep roots make transplanting mature plants difficult or impossible. Aside from plenty of sunlight and nutrient-rich soil, you’ll want to make sure they are planted in an area where you can enjoy their gorgeous flowers. Herbaceous and intersectional varieties should be planted in a spot with at least five to six hours of full sun per day. However, plants that produce single and anemone flower forms may benefit from some afternoon sun protection. Furthermore, because they hate wet feet (roots standing in water), plant them somehwere with excellent drainage, like a slope or raised bed. And don’t forget to plan ahead and give tree peonies plenty of room—most grow to five by five feet in their 10th year.

Tip: The experts from the University of Michigan’s Peony Garden at the Nichols Arboretum recommend planting them far away from large trees and shrubs as they do not like to have root competition.

What type of soil is best for peonies?

Some gardeners have success growing them in their native soil, but most experts recommend amending with organic matter before planting. Proper soil preparation will make it so you don’t have to fertilize for the first few years. No matter what, ensure that they have well-drained soil, as they will not do well with soggy roots.

Here are some tips for improving your soil:

• Herbaceous varieties love potassium; a 5-10-10 slow release fertilizer is a good choice.
• They are heavy feeders and prefer alkaline soil, which may require adding garden lime or wood ash.
• Additional trace minerals (such as Azomite®) will inspire tree peonies to increase their flower size, bud count and ratio of double flowers, and to intensify flower color.

How deep to plant a peony:

The depth at which you plant your peony will depend on the type and your climate.

Here are the ideal planting depths for each type:

• Herbaceous: Position these with their “eyes” (next year’s buds) ½ inch (in warmer zones) to 2 inches (in cooler zones) below the soil surface.
• Tree: Plant deeper than herbaceous types. Experts suggest digging a hole 2 feet deep and 1 foot wide (after amending the soil with organic matter). Position with the graft 4 to 6 inches below ground level, so that the “nurse” herbaceous peony rootstock will die away.
• Intersectional: Plant them just below the soil surface, 1/2 inch deep in warm zones, 1.5 inches in cooler zones.

Can they be grown in a pot?

While they are happiest in the garden, they can be grown in pots if given the proper attention. Select a large container with plenty of drainage holes. In colder areas, bring potted peony plants in for the winter to protect them from freezing temperatures; plants in containers are more susceptible to frost damage. Additionally, you will need to water more frequently during the growing season, as containers dry out quickly.

Herbaceous and intersectional peonies should be cut back in the fall. Photo by: photowind / Shutterstock.

Should I prune my peony?

Unlike roses, peony bushes do not require precise pruning to thrive. Often pruning is only necessary in the event of damage or disease. Both herbaceous and intersectional types should be cut back at the end of the growing season. Cut your herbaceous peonies all the way to the ground, but leave 4 to 6 inches of stem on your intersectionals.

For tree peonies, a dense snarl of branches can lead to doom. After five years, remove suckers from the center of the shrub to thin out growth and promote better air circulation. Do not cut back until they are well established—they are slow growing, so every inch is precious. Pruning during the first two to three years will just hinder their progress and slight you on next year’s display. When pruning tree peonies, take care not to cut the woody stems—they bloom on old wood.

Disbudding peonies:

If you want large flowers, remove the side-buds that develop near the base of each terminal bud. However, if you want to prolong the blooming season, leave the side-buds alone (they will bloom later than the terminal buds).

Can I divide my peony?

Peonies do not need regular division for successful blooming. However, if you’d like to have more, you can divide your mature plants as a form of propagation. The best time for dividing is in the fall when the plant is nearing dormancy. Roots cut into pieces with 3-5 eyes have the best chance of success. Learn more about dividing peonies.

Do peonies require complex staking?

Many should be staked to support heavy blooms, especially if you live in a rainy climate. Herbaceous varieties can be supported with a peony ring, while tree peonies are more suited for the use of bamboo stakes and natural twine. If this sounds like too much hassle, there are many varieties that feature strong stems that don’t require staking.

How often should I water my peony?

They are not overly thirsty plants—in fact, overwatering can lead to problems. Give your peony bush excellent drainage and begin watering in spring if you go more than two weeks without rain. Then, provide weekly, deep watering throughout the dry summer months (one inch at each watering). Continue watering after flowering to ensure vigorous plants the following year. There is no need to water once they have gone dormant.

Should I mulch?

In very cold climates, they may benefit from a loose winter mulching with organic matter such as pine needles or shredded bark. Keep mulch a few inches away from the base of the plant. Remove the mulch in spring to allow new growth at the soil surface. For tree peonies especially, winter protection with burlap and a 3 to 4 inch layer of mulch (pulled aside in the spring) is wise in Zone 4 and colder parts of Zone 5.

Why didn't my peony bloom?

Many gardeners have difficulty understanding why their peonies don’t bloom. Here are the most common reasons:

• They are planted too deeply
• There isn’t enough sunlight
• Your soil is heavy on nitrogen
• The plants are still young

Ants:

Peony buds secrete a sweet nectar that attracts ants. The ants do not hurt the plant and they aren’t required for the blooms to open. If cutting flowers to take indoors, gently rinse the blossoms in a bucket of water to get rid of the ants.

Leaf curl:

When a peony's leaves curl it is a sign of stress, caused by lack of water, a virus or unusual weather conditions. Many plants recover from leaf curl if the issue is corrected and go on to bloom normally.