Peonies are one of the most beloved and longest living perennial flower. Their flowers range from exquisitely delicate singles to large and lush doubles and come in shades ranging from pure white to the deepest, darkest red imaginable. This extravagant display is produced every year, at the absolute peak of bloom in most gardens, regardless of the weather, because Peonies are among the most durable and trusted garden perennials. This paper will discuss general information, methods of propagation, and future needs that will lead peonies into future gardens everywhere.

Introduction
Few plants are as popular as the peony (Paeonia spp.) in American perennial gardens. For centuries the peony has been the “grande dame” of flowers. Native to Eurasia and North America, peonies are renowned for their uniquely graceful shape. Hardy perennials of both herbaceous and shrubby tree form, peonies continue to be one of the most popular flowers. Peonies are grown in temperate regions for their showy single or double blossoms in shades of yellow, white, pink, and rose. They traditionally bloom in late May and early June. The herbaceous types show long lasting blooms, which are traditionally excellent for cutting. The decorative foliage will endure well until the first frosts. Five wild species all native to China account for a majority of the hybrids available today: Paeonia lactiflora, P. officinalis, P. peregrina, P. tenuifolia and P. wittmanniana. The Chinese perfected the peony a thousand years ago; almost to the degree we know it today. Most of the showy garden hybrids were derived from P. officinalis. There are five recognized types of flowers: Single, Japanese, Anemone, Semidouble and Double.

Landscape Placement
Peonies must be planted in deep, fertile, humus-rich soil that will not dry out quickly in the heat of the summer. Before planting, enrich the soil by adding well-rotted manure or garden compost (not barnyard manure – this will stimulate decay of the fleshy roots). They are able to tolerate light shade, but will do much better in full sun. Tall growing Peonies should be provided with grow-through support early in the season. It is beneficial to mulch the soil around your plants with decayed manure in the spring. This feeds them and helps to keep the roots moist. If mulch is placed over the roots in autumn, it should be light to allow the circulation of air; salt hay or evergreen branches can be laid lightly over the ground. Adding rotted manure, peat moss, or other material, which are likely to hold water, will encourage disease. When Peonies are planted, they should be set so that their crowns are 2 inches under the soil. Peonies need plenty or room to grow so they should be spaced 21/2 -3 feet apart. Peonies will produce larger flowers if all the flower buds, except the terminal one, are removed early.

Methods of Propagation
Peonies may be propagated in several different ways.An unusual and uncommon method is by seed. It often takes 5-7 years to produce a flowering plant from seed. The time one invests in starting peonies from seed is justified by the disease free stock plant that will grow for many years. A well established, healthy root system in fertile soil may bloom as long as 50 years. The easiest and most popular method of propagation is division of the roots of established plants. Root division should take place in the fall when the plant is dormant. September is the best planting and dividing time for peonies in North Dakota. Roots set in September usually become established before the cold weather begins. A thick division of an old, established plant should not be expected to flower the first year after planting. The large clumps may be cut into sections containing 3-5 eyes (buds). These divisions should be set 1 - 2” below the soil surface. Deeper planting of the divided roots delays or inhibits flowering. 
 

Care and Maintenance
Mulch peonies each spring with a 2- to 3-inch layer of organic matter to control weeds, conserve moisture and to keep the soil cool. In the fall, remove and destroy the old mulch to aid disease control. Leave the plants unmulched during the winter .Maintain adequate phosphorus levels in the soil for healthy, vigorous root development and growth. Soil test every 3 years to monitor for essential nutrients. Apply a low nitrogen fertilizer such as 5-10-10 at the rate of 2 to 3 lb per 100 ft2 (2 Tbsp per ft2 1/2 cup per plant) in the spring when the stems are about 2 or 3 inches high. Over-fertilization, especially with nitrogen, usually results in weak stems and reduced flowering.
To produce larger flowers, a practice known as disbudding is recommended. The terminal bud on each stem tip is left and all side buds are removed. This should be done as soon as the buds are visible. To prevent the large flowers from breaking or bending over during a strong wind or rain, plants should be staked. Sink the stake behind the plant and use stakes that are 6 to 12 inches shorter than the plants so they will not be visible. Loosely tie the stems to the stake using plastic covered wire or a soft cloth. Tie the stems, making a double loop, with one loop around the plant and the other around the stake.
Remove flowers as soon as they fade to prevent seed development, which can use up needed food reserves. The faded flower should be removed just below the flower, leaving as much foliage as possible. Cutting flowers for enjoyment in the home can also reduce the flowering in future years. Do not cut more than one-third to one-half of the flowers for cut flowers and leave as much foliage as possible on the plant.
In the fall, after a heavy frost, remove and destroy the stems of garden peonies down to 3 inches from the soil surface to eliminate the possibility of the fungal diseases overwintering.
Peonies do not respond well to transplanting and reestablish slowly. Divide and replant only after they become crowded — usually after 10 to 15 years. Fall is the best time to divide when swollen red buds are clearly visible. Carefully dig around and under the plant to avoid cutting off roots. Cut tubers with a sharp knife that has been sterilized with a flame or in alcohol. Each section should contain 3 to 5 eyes. Dust cut surfaces with fungicide to discourage disease infection and rot.

Potential Problems
No flowers — Peonies that were started with small tubers or were recently transplanted (especially in the spring) may fail to develop flowers for several years. Planting the tubers more than 2 inches deep or in a shady or poorly drained location can also prevent or reduce flowering. Other possibilities include tree and shrub root competition and late spring frosts. If your peonies have been planted too deep, you may speed up the flowering time by resetting them, but if they have been in place several years, they may be nearly ready to bloom since 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 may bloom sparsely. If this is the problem, select a new site in full sun. Shade that did not exist at planting time could develop over a long period of time, gradually creating problems with reduced blooms over the later years of the plant.
Botrytis blight — This is caused by a fungus that overwinters on dead leaves, stems, and roots. The disease usually appears in mid-summer, especially during cool, wet weather. Black, soft buds and wilted or soft stem tissue under the buds are usually an indication that botrytis blight is present. For control, remove diseased foliage that develops during the growing season and cut plants to the ground after a killing frost (in September or October) and destroy the foliage.
Phytophthora blight — This is less common than botrytis blight but can be more devastating. Black leathery spots fist occur on the buds. Stems dry up turning brown and leathery; plants may rot at the ground line or crown. Control measures recommended for botrytis blight should be followed.
Leaf spots — Several fungi can cause leaf spots on peonies. Leaf blotch is a disease that usually occurs after flowering. Infected plants have small red or reddish-brown spots that later enlarge into purplish-brown blotches on the leaf surface. Destroy affected foliage as it occurs and all foliage after a killing frost.
Virus — Mosaic virus produces yellowish blotches and rings on the foliage. Infected plants are not dwarfed or deformed. Destroy infected plants to prevent spread.
Ants — Ants often will feed on the sweet, sticky secretion that covers the flower buds. Very little direct damage results from their feeding.
Thrip — Insects such as thrips can cause flowers to become deformed and not open. Apply the appropriate insecticide if thrip activity is noted, following label instructions.

Future Work Needed
From the gardener’s point of view, the most exciting news is that by careful selection of today’s cultivars, six to eight weeks of continuous bloom is possible. There are also more colors than ever before. The development of these new hybrids is hindered only by the fact that peonies are slow to propagate. By present methods it can take fifteen to twenty years for a new cultivar to become widely available. One solution may be tissue culture. But whereas other perennials are easy to propagate by the tissue culture method, peonies remain somewhat elusive. Research may lead in the direction of tissue culture method for propagating peonies.
 

Varieties

Descriptions are of the flowers. P. emodi (single, white); P. cambessedesii (single, deep rose-pink); P. mascula (single, carmine, purple-red or white w/ golden stamens & purple filaments); P. veitchii (small, single, purple-pink); P. smouthii (single, dark crimson w/ yellow stamens); P. tenuifolia (dark crimson w/ golden stamens - very attractive & delicate, bright green foliage); P. wittmanniana (single, pale primrose yellow w/ yellow anthers & purple filaments); P. mlokosewitschii (single, pale lemon to creamy yellow); P. suffruticosa (Tree Peony - white blotched w/ crimson); P. anomala (rose); P. humilis (rose); P. lutea (Tree Peony - yellow).
P. lactiflora & var. White Wings (semi-double, white, ruffled, sometimes tinged w/ light yellow), Whitleyi Major (single, ivory white w/ golden stamens), Baroness Shroder (double, globular, flesh pink fading to white), Krinkled White (single, white sometimes stained w/ pale pink w/ golden stamens), Duchesse de Nemours (double, green tinted outer petals fade to white, white inner petals w/ yellow base), Alice Harding (very lg., double, white), Cornelia Shaylor (double, ruffled, opens flushed rose pink turns to blush white), Shirley Temple (double, ruffled, outer whorls of pale rose pink fade to buff-white with smaller inner petals), Mother of Pearl (single, rose pink petals paler edges w/ golden stamens), Sarah Bernhardt (double, ruffled, rose-pink fades to silvery pink on edges), Kelway's Supreme (double, blush pink fade to cream white w/ golden stamens), Avant Garde (single, pale rose pink with darker veins w/ gold anthers & red filaments), Ballerina (double, ruffled, more compact inner petals, pale blush pink, lilac tinted at first, fading to white), Bowl of Beauty (anemone-form, pale carmine pink w/ ivory white stamens), Globe of Light (anemone-form, pink w/ golden stamens), Kelway's Gorgeous (single, bright carmine stained w/ salmon pink), Magic Orb (double w/ several whorls of ruffled, cherry pink outer petals & pale blush white inner petals shaded w/ carmine), Silver Flare (single to semi-double, carmine pink fade to silvery margin), Auguste Dessert (double, carmine pink tinged w/ salmon pink w/ ruffled silvery white petal edges), Instituteur Doriat (anemone-form, carmine red outer petals & pale pinkish-carmine tipped w/ silvery white inner petals), Defender (single, satiny crimson), Knighthood (double, deep, rich burgandy-red), Chocolate Soldier (single, dark purple-red), Sir Edward Elgar (single, crimson tinted w/ chocolate brown), Laura Dessert (double, blush white outer petals, lemon yellow, ruffled inner petals).
P. officinalis & var. Alba Plena (double, ruffled, white tinged w/ pale pink), China Rose (single, dark salmon-rose w/ golden orange anthers), Rubra Plena (double, bright pink-crimson).
P. peregrina & var. Sunshine (single, vermilion tinted w/ salmon rose).

Written by Eric C. Brown

North Dakota State University - Dept. of Plant Sciences

Plant Sciences 211 Lab
 

NDSU

North Carolina Cooperative Extension Service

White Flower Farm Online Garden Catalog

References
Apps, Darrel, editor. Perennials.Hearst Books: New York. 1993.
Smith, Ronald C. “Popular Peonies!”. NDSU Extension Service Publication. Jan., 1994
Still, Steven. Manual of Herbaceous Ornamental Plants. Stipes Publishing. Dec, 1993.
White Flower Farm Online Garden Catalog. Accessed 10 October 2003. <http://www.whiteflowerfarm.com/default.asp>