By: Darcy Larum, Landscape Designer
With so many varieties of peonies available these days, selecting the right peony for your garden can be confusing. This article is specifically about growing tree peonies.
Herbaceous peonies are perennial peonies that die back to the ground each year. The roots remain dormant under the soil, then the plant stems push up in the spring. Tree peonies are woody, deciduous shrub peonies. They lose their foliage in the fall but their woody stems do not die back to the ground like herbaceous peonies. Itoh peonies are a hybrid cross between herbaceous peonies and tree peonies, they do die back to the ground in fall like herbaceous peonies but their flower and growth characteristics are similar to tree peonies.
Native to China, tree peonies were valued as a medicinal plant long before they were adored ornamentals. Tree peonies are larger, woody relatives of the common herbaceous peony, growing up to 5 feet (1.5 m.) wide and tall in about ten years. They are highly prized for their large, prolific blooms that can grow up to 10 inches (25+ cm.) in diameter.
These flowers, which bloom in late spring to early summer, make excellent cut flowers and come in single or double forms. Unlike herbaceous peonies, the flower buds of tree peonies do not produce the sweet honeydew sap that attracts ants.
While some varieties of tree peonies are hardy down to zone 3, most tree peonies are hardy in zones 4-8. They do best where they have a cold winter for dormancy and hot summers. Usually labeled as full sun plants, tree peonies prefer some dappled to light shade from the hot afternoon sun. Too much intense sunlight can cause the beautiful flowers to fade and wither quicker.
They prefer slightly alkaline soil and proper drainage is essential. Tree peonies also prefer a site where they do not have to compete with roots from other shrubs or trees. They do best with perennial companion plants.
New tree peony plants should be planted in spring or fall, not during the heat of summer. They can be slow at first to get established, sometimes taking up to three years to grow much or bloom. Once established, tree peonies are drought tolerant and do not transplant well. A properly placed, content in its environment plant can live up to a hundred years.
Tree peony care in gardens is not any more complicated than herbaceous peony care. However, unlike herbaceous peonies, tree peonies should never be cut back in autumn. Tree peonies should only ever be pruned or cut back to shape or remove dead, damaged or diseased wood.
They have high iron and phosphate needs and may benefit from an annual feeding of iron sulphate and bone meal in spring. Tree peonies should also be fertilized regularly with a general purpose fertilizer that is higher in phosphorus than nitrogen and potassium, like 5-10-5.
Tree peonies can be susceptible to fungal diseases, so it’s best to water them directly at the root zone. They can also be damaged by borers, so check regularly for signs of borer holes in the wood.
Before winter, apply a protective layer of mulch over the plant’s root zone.
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Please take time to prepare your planting area. In return you will receive a lifetime of enjoyment. In 10 years, most plants will grow to 4' x 4'. If planting a group of tree peonies, allow at least 4-5' between them. Do not plant closer than 8-10' from large trees, where tree roots will compete with the peonies for nutrients and water. Choose a location with 4-6 hours of direct sun or dappled sun/shade all day. Full sun will make the flowers fade rapidly. Full shade will result in weak and slow growth.
This is the most common misunderstanding. Tree peonies do not have watering needs like roses or other perennials. They are woody shrubs native to northern China, which receives about 30 inches of rain per year. Once established, tree peonies are drought tolerant plants. Excess water will suffocate the roots and is the leading cause of plant failure. Do not plant near auto-sprinkler systems that keep the soil continually moist. Do not water until soil is dry below the surface and try not to wet leaves when watering to prevent fungus. Be observant вЂ” soil can dry out on top and still be moist 6-12" below the surface. When you feel the soil is dry below the first 4-6" and leaves may droop slightly, water the roots deeply. Climates of hot summer temperatures with little or no rain at all will require more attention to watering than those areas that get some rainfall. Peonies in root control bags will require more watering attention than tree peonies planted in the ground. Of particular importance, droopy leaves in the first warm days of spring are caused by an imbalance of the roots and leaves. If soil has moisture, do not water. This is an imbalance that will self correct as the plant settles into the growing season. You know this is the cause of the limp leaves if the plant recovers in the evening or early the next morning. Failure to follow these directions on watering will give unsatisfactory results.
In areas of damp, cold, spring weather, using a copper spray will prevent fungus which discolors the leaves with black spots later in the season. Use Basicopв„ў sold in most garden centers, or Soap ShieldВ®. Mix according to package directions. Use in early spring when the buds start to open, 3 treatments, 10 days apart. This will prevent spotting that shows up later in the season. If you do see fungus in late spring or summer, remove damaged leaves. Late season spraying seems to have no effect on peonies. Spraying must be used preventatively. This fungus rarely kills the plant, but will slow its growth. If you have a problem one year, remember to treat for it early the following season.
For optimum growth and vigor, fertilize every 2-3 weeks with 1 oz. to 1 gallon of fish/seaweed fertilizer such as NeptuneвЂ™s Harvestв„ў. If it is raining frequently, mix 1 oz. fish/seaweed to 1 cup of water and sprinkle at the drip line of the plant, letting the rain pull the food to the roots.
The hot weather is a time of dormancy, with little or no leaf growth. Plants are storing energy in the roots and will make buds for next season in late summer. Continue to fertilize plants until about one month before the frost date in your area. Water plants when it seems dry 4-6" below the surface of the soil water deeply, allowing plants to dry out again before the next watering.
About the time of the first frost, remove the leaves to prevent any over-wintering of fungus. Do not cut the woody stems вЂ” flowers will bloom in spring on this old wood. Check for borer at this time. You will sometimes find a hold drilled into the woody stem on older plants. The pest known as the вЂњRose BorerвЂќ will sometimes drill into the pith of larger stems. Cut off the affected area or take a thin wire and poke into the hole, killing the larvae. Seal the hole with white glue or clay. After fall clean up, we like to add a little compost and a cup of lime to acidic soils. Lightly dig in around the drip line. Tree peonies in China grow in soil with a pH of 7.0 or higher, so we feel it is important to maintain pH at this level for optimum growing conditions.
Mulch plant well in zone 6 and colder parts of zone 7. Warmer climates seem to be fine with little or no mulch once plants are established.
Once your tree peony is growing for several years and has many branches, it may be necessary to cut out extra growth in the interior of the shrub. Select 6 to 10 of the strongest branches as the major stems of the plant. This will allow the peony to concentrate its strength on flowering in its main branches, rather than excessive leaf growth. It will also eliminate chances for fungus to grow, allowing more light and air to circulate in the plant. If you prefer to see the wood of the tree peony at the base, you can prune out leaf buds low to the ground this is a Chinese style of shaping. The natural habit for most Chinese tree peonies is a very dense, spreading, rounded form.
Remember the Chinese proverb, вЂњThe gardenerвЂ™s footsteps are the gardenвЂ™s best fertilizer.вЂќ
Herbaceous, Intersectional, and tree peonies thrive with the same general care. There are some slight differences in the preferred range of sun as noted below.
Soil All peonies prefer a fertile, well-drained soil. They do not like to have wet feet, so heavy, poorly-drained clay is not advisable. Sand does not hold enough nutrients or moisture, so peonies planted in sand will also suffer.
Nearby Plants Herbaceous peonies do not like to have root competition. Plant them far away from large trees and shrubs. Plant other herbaceous material at least 12 inches away from the crown of the plant. Tree peonies can tolerate other trees and shrubs, but too much shade is detrimental.
Fertilizing If you would like to fertilize your peony, you can use tulip fertilizer. This will provide nutrition to the plant and encourage blooming. Fertilize in the spring when plants are emerging from the ground. Add the fertilizer around the drip-line of the plant - not directly on the crown which can burn the plant.
Watering Once established, peonies require very little water. However, during the first year, it is critical to provide enough water. Mature plants can benefit from a deep watering during especially dry periods. Remember, peonies do not like to be sitting in water, so be careful not to overdo it.
If planted well, herbaceous peonies will happily send up new shoots each spring for decades. Photo by: gutaper / 123RF.
Bare root peonies are best planted 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.
Picking the right spot is essential for success. Established peony plants have deep roots that make transplanting difficult or even impossible. Peony plants need a location with:
You'll also want to make sure they are planted in an area where you can enjoy their gorgeous flowers.
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.
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:
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:
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.