Cultivation Techniques and Management Methods for Peonies

China is the place of origin of the peony, and peonies are also deeply loved by people. In order to better develop peonies and give play to their ornamental value, this article starts from the cultivation history of peonies, analyzes the morphology and ecological habits related to peonies, and discusses peony cultivation techniques through an account of peony propagation methods, cultivation management, and flowering period regulation.

Cultivation History of Peonies

Since ancient times, the peony has been called the king of flowers, known as “national beauty and heavenly fragrance,” and has the title of “wealthy flower.” Peonies have a long cultivation history in China, spanning more than 1500 years. During the Tang Dynasty, they were already a precious flower in the imperial palace, and a special peony garden was established at Lishan. By the Ming and Qing dynasties, peonies in the middle and lower reaches of the Yellow River, peonies in Bozhou, peonies in Caozhou, peonies in Jiangnan, and peonies in Lanzhou all shone brilliantly, truly pushing the peony to the status of “king of flowers.” Now, in countries such as China, the United States, Japan, and the Netherlands, new commercialized potted peony varieties have been bred through crossbreeding.

Biological Characteristics of Peonies

1. Morphological characteristics. The peony belongs to the Paeoniaceae family and is a deciduous small shrub. The stems are generally 1 m to 2 m tall, and the tallest can reach 3 m. The branches grow in clusters from the ground, with obvious nodes and leaf scars. It has a fleshy taproot system with no lateral roots growing horizontally. The leaves are bipinnately compound with three leaflets per division, dull green on the surface, hairless, with a white bloom on the underside, nearly hairless. The flowers are solitary at the tips of the branches, large, 10-30 cm in diameter. Currently cultivated varieties are mostly double-flowered, with rich flower colors including yellow, white, red, pink, purple, and green. The flowering period is April to May. The fruit is a follicle, and the seeds are black. The fruit ripening period is from mid-August to early September.

2. Ecological habits. The peony is a cultivated species, and the original species of peony is produced in northwestern China and the Qinling area. It likes cold winters that help dormancy and mild summer climate conditions that are favorable for flower bud differentiation. It is relatively cold-tolerant but not heat-tolerant. It can usually tolerate low temperatures of -20 degrees, but temperatures above 32 degrees have adverse effects on peonies. It likes light, but does not like exposure to the western sun. Its roots are fleshy, and it likes dryness and dislikes dampness, fearing waterlogging. It is suitable for fertile, loose, well-drained soil, and the soil pH value is suitable when neutral or acidic; it can also grow normally in alkaline calcareous soil, but saline-alkali soil is taboo. The plant grows slowly, and the new shoots wither every year, showing the phenomenon of “branch dieback,” hence the saying “the peony grows one chi and retreats eight cun.” Seedling plants generally take 5-6 years.

Cultivation Techniques for Peonies

1. Propagation methods

(1) Division propagation. Asexual propagation can keep the excellent traits of the mother plant basically unchanged, and the propagation of ornamental peonies mainly uses this method. Peonies do not have an obvious main trunk and are clustered shrubs, very suitable for division, and it is also relatively simple and easy to carry out. The method and steps are as follows:

① Choose a suitable time for division. Peony division is generally carried out from late September to early October, during which the ground temperature is very suitable for the formation of new peony root systems. If divided and planted too early, because the outside air temperature is still high, it is easy to cause winter buds to sprout and send out new branches, namely “autumn growth,” which not only consumes nutrients but also reduces cold and drought resistance, and is very unfavorable for growth and flowering the following spring. If divided and planted too late, the new roots are weak or no new roots are produced, the plants grow weakly the next year, with few tillers, short and thin branches, and they are very likely to die when encountering drought.

② Division method. Peonies can be divided and propagated after growing for 3 years, but 4-5 years old is preferable. First dig the mother plant out of the ground and dry it in the sun for 1-2 days so that the roots lose water and soften, but do not dry them in the shade excessively. Split them apart at places that are easy to separate. The lower part of the new division should have a relatively good root system, and each plant should have 3-5 tiller buds. After division, plant in pots, and after 5-6 years they can be divided again. Before planting, the old branches on the upper part of the divided plant should be cut off 3-5 cm above the root crown. If the divided plant has no sprouting tiller buds or has too few, thin and weak tiller buds, then 2-3 latent buds should be left below the cut site. The purpose of cutting off old branches is mainly to avoid the consumption of nutrients in the roots by the leaves and flowers of the old branches, promote tillering, and enhance the growth vigor of the divided plant.

③ Planting method for divided plants. Quickly dip the divided plants in a mixed solution of isofenphos-methyl and Lvheng No. 1, and plant them after drying. At the same time, in order to stimulate the formation of new root systems, rooting agents such as indolebutyric acid and naphthaleneacetic acid at 50-200 mg/L can be added to the mixed solution, which can promote rooting and enhance growth vigor. When planting, use the method known in forestry production as “three burials, two tampings, and one lift,” that is, first place the seedling vertically into the hole and position its roots well, then with one hand gently lift the seedling while with the other hand fill soil into the hole. When the soil has been filled to half the hole, gently lift the seedling upward with the hand, gently shake it left and right once, so that fine soil closely contacts the roots, then use a wooden stick to firm the soil around the seedling, then fill the hole full of soil and firm it, and finally fill the planting hole completely. After planting, use loose soil to seal the planting hole into a mound, generally 15-20 cm above the ground.

(2) Grafting propagation

The main considerations are several aspects such as grafting time, rootstock, scion, and grafting method.

① Grafting time. Peonies can be grafted from late September to early October, and the period from White Dew (September 7-8) to Autumn Equinox (September 23-24) is suitable. In particular, the survival rate is highest when grafting around White Dew. This may be a response of peony grafting to specific temperature and humidity. Around White Dew, the air temperature is 20-25°C, and the ground temperature at 30 cm depth is 18-23°C, so the graft union heals quickly and produces callus tissue, resulting in a high survival rate.

② Selection of rootstock. The rootstock is usually peony root or herbaceous peony root. Using peony root as the rootstock, because it is relatively fine and hard, grafting is not convenient, and the propagated plants grow relatively slowly at first, but the base of the scion is relatively easy to root, and there are also relatively many tillers, which is beneficial for future division, and the lifespan is also relatively long. Using herbaceous peony root as the rootstock, because its lignification is relatively weak, operation is more convenient, and the survival rate is also relatively high. However, the scion roots produce relatively few roots, and there are not many tillers, and the lifespan is also relatively short. The rootstock should be dried in the sun for 1-2 days, and grafting should be carried out after it loses water and softens, so that the cut is not easy to split and is convenient to handle.

③ Scion. It is best to use branches grown from soil buds as the scion. Their tissues are full, their vitality is vigorous, new roots and new branches are easily produced at the base, and the survival rate after grafting is high. If there are very few sprouting tiller branches, only one-year-old branches from the upper part of the crown can be used as the scion. The scion length is generally 5-10 cm, the thickness is more than 0.5 cm, and it carries 2-3 full and plump buds.

④ Grafting. After cleft grafting or cut grafting, bind with hemp rather than plastic film strips, coat with mud slurry, and plant into a deep and wide pot. The pot soil should be moist, and generally no watering is done after planting; cover with soil to preserve moisture.

(2) Seed propagation

It is commonly used when breeding new varieties of ornamental peonies, but not for medicinal peonies. When the peony fruit ripens, it naturally splits open and releases black seeds, so the fruit should be collected before the follicle is about to split. Place the collected fruit in a sieve to dry in the sun, and after collecting the seeds in September, sow them immediately. Be careful to keep the soil moist. After the seeds overwinter in the soil, due to the stimulation of low temperature, the epicotyl elongates the following spring, and the seedlings emerge from the soil.