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Popular Peonies (H281 (Revised))

Peonies are among the most adaptable perennials for North Dakota. They include a variety of flower forms with beautiful colors and attractive foliage that remains long after the flowers have faded.

Esther McGinnis, Horticulturist NDSU Extension Service

Ronald C. Smith, retired Extension horticulturist, NDSU


Peonies

Peonies can serve as an interesting accent along a shrub border, fence or wall; if planted close together, you can create an informal hedge effect. This works well as a subtle divider between lawn areas, a shrublike backdrop for annual flowers or a border along a driveway or property line. Peonies can substitute for low-growing shrubs in locations in which snow may be a problem because the tops are removed in the fall.

Peonies combine well with other perennial flowers by providing a season of color during June. Plants that pair well with peonies include irises, catmint and coral bells.

Soils and Where to Plant

Peonies thrive in any well-drained, rich garden soil. Poor soils can be amended with compost or peat moss. Plants will flower best if they receive at least six to eight hours of sunlight per day. Peonies do not compete well with grass or tree roots for water.

Planting, Spacing and Cultivation

Late August through early September is the best time for planting bare-root peonies in North Dakota. Early fall planting allows roots to become established before cold weather. Three to five healthy buds (eyes) per root are desirable. See Figure 1.

Planting depth 

Figure 1. Not more than 2 inches of soil should cover the top bud. Peonies set deeper than 2 inches may make excellent foliage growth but often fail to bloom satisfactorily.

To maximize root development, prune off all flower buds in the year after planting. Plants may be allowed to flower in the second year. By the third and fourth years, the plants should flower prolifically.

In contrast to bare root, peonies purchased in containers are best planted in the spring or early summer. As described above, make sure that no more than 2 inches of soil covers the eyes.

Healthy plants in fertile soil may bloom for 50 years or more. Plants should be spaced 3 to 4 feet apart to accommodate vigorous growth. Closer spacing will necessitate transplanting. A 2- to 3-inch layer of leaf or straw mulch applied in the fall after the ground freezes is desirable the first year for newly set peonies. Remove this mulch about April 1.

Cultivation should be shallow, just to keep the weeds down. Cultivating more than 2 inches deep likely will injure the shallow peony roots.

Propagation

When old, established peony clumps become too crowded, flowering may be reduced, so you should divide the roots. In early September, cut the stems near ground level and dig the roots carefully with a spading fork. Shake the roots to remove loose soil and then wash off most of the soil. Washing the soil away helps you locate natural crown cleavage areas so you lose less of the fleshy roots while dividing the clumps. Each division should have three to five healthy eyes (buds) attached to three or four thick roots.

Fertilization

Peonies are very heavy feeders. Barnyard manure should not come in contact with the peony roots or shoots. Such contact may stimulate decay of the fleshy roots. However, you may use composted manure to improve the soil if it is applied to the soil surface in a 1- to 2-inch layer.

A couple of tablespoons of 10-10-10 fertilizer worked into the soil around each established plant in early spring is beneficial. Keep the commercial fertilizer 6 inches away from the stems of the plant and then water to dissolve the fertilizer.

When to Cut Blooms and Staking

Blooms for bouquets should be cut as soon as the outer petals unfold. Do not remove large amounts of the leaves when picking flowers. Leaves should be left on the plant to manufacture food for the next season’s growth and bloom.

Place blooms in a container as soon as they are cut. Snip the stems ½ inch shorter under water. This prevents air bubbles in the end of the stem and lets the blooms last longer.

Peonies in full flower often are top-heavy, especially after a rain. You can prevent unsightly flower drooping by staking the plants. Thin wire hoops can be fastened to three or four stakes to provide an economical support. Tomato cages also work. These should be installed in early May before your plants get too large. Remove spent blooms and stems to the foliage line as flowers wither.

Why Peonies Fail to Bloom

Peonies fail to bloom satisfactorily for several reasons, including being planted too deeply, shading, diseases (such as botrytis and viruses) and insects (thrips).

If your peonies have been planted too deeply, you may accelerate flowering by resetting them, but if they have been in place several years, they may be nearly ready to bloom because the plant “lifts” itself a little each year as it grows.

Shade from buildings or trees may result in weak plants that fail to produce flowers or bloom sparsely. If this is the problem, select a new site in full sun. Shade that did not exist at planting time could develop during a 20-year period, gradually creating problems with reduced blooms in the last few years.

Botrytis blight is caused by a fungus that overwinters on dead peony leaves, stems and roots. The easiest control is sanitation, which means completely removing the plant tops in September or October. Bury, burn or send the tops to the landfill.

Some virus diseases may stunt and deform the growth of your peonies and cause a gradual decline. Each year, the plant becomes shorter and somewhat discolored, and may fail to bloom. Remove such plants and destroy them.

Certain insects such as thrips can cause flowers to become deformed and not open. Apply the appropriate insecticide if thrip activity is noted. Make sure to follow the instructions on the insecticide’s label.

Cultivars

Hundreds of peony cultivars are available. The following table lists recommended cultivars by form and petal color. Common peonies such as ‘Sarah Bernhardt’ and ‘Festiva Maxima’ are not listed due to their weak stems.

Cultivar table

 

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