Cultivation

Chinese Mudan have a wide ecological adaptability so that their cultivation is easy and conveniently managed. They can be grown both in gardens and in pots in all parts of China with the exception of Hainan, the southernmost province.

1. Selection of Appropriate Cultivars and Sites

The four cultivar groups of Chinese tree peonies have ecological characteristics and soil conditions that suit them best. Before planting, suitable sites or the properties of a cultivar group and its individual varieties should be considered for future cultivation and management to ensure success.

Chinese peonies are classified as temperate plants. They tend to thrive in

cool, dry and sunny places. As they have prominent long fleshy roots, the best choice for their cultivation is a dry and airy site on higher ground, with lateral shading, good drainage and deep porous fertile soil. Uncultivated or sticky or saline earth and poor drainage are best avoided. But different cultivar groups, and cultivars in a group, can to some extent be suitably matched with the ecological environment. In addition, land that has been cropped continuously with peonies should be replanted with peonies after one to two years rotation. After the site has been selected, a generous quantity of manure should be applied and deep digging and leveling should be repeated several months or half a year before planting. The ideal soil for planting in pots is also loose, fertile, well-aerated and well-drained. Future developments in pot cultivation are likely to involve artificial nutrients and an inert medium such as perlite.

2. Planting

Autumn is the best season for planting peonies, because it helps early development of new roots and thus early recovery of plant vitality for normal growth in the next spring. If a peony is divided and planted in spring, its root system cannot recover before the onset of rapid growth and development of the parts above ground. Thus the nutrient supply cannot match the need and the plant may greatly lose its vitality, and as a result normal growth and flowering will not return until after several years' cultivation. Planting should take place during the period from mid September to the end of October. The earlier part of this period is better, because the soil temperature is still high then and this benefits the early growth of new roots from divided plants,which ensures then-winter survival and development the next year. Excessively early planting may result in "autumn bud-burst" -shoots that develop into branches too soon and which will be damaged by cold during winter, because they have not lignified. Very late planting is disadvantageous to new root development which results in slower recovery and a lower survival rate.

If possible, planting should be carried out promptly after division. The planting space should be broad and deep. Well-rotted manure dug in with the bottom soil will encourage the root system to distribute evenly. The correct planting depth is with the collar the same level as or slightly below the earth surface. Soil should be trodden in layer by layer. Finally the plants are thoroughly watered.

3. Irrigation and Feeding

Chinese peonies consume a great amount of nutrient and also transpire a great deal because of their luxuriant branches and leaves and huge flowers, and although they thrive in a dry environment they do not grow well without moisture. The principle of watering is to keep soil moist but not too wet and definitely not flooded. Generally, newly planted seedlings should be thoroughly watered, while watering of established plants should be related to the growing environment and individual flower conditions. In northwest China, for example, there is less annual rainfall than elsewhere. Less rain in the dry spring and less rain and snow in the long winter mean that the supply of an appropriate amount of water and attention to soil moisture conservation are particularly important there.

The application of fertiliser in proper amounts and at the proper times not only facilitates plentiful flowers of large size, bright colours and full flower forms, but also prevents or reduces the differences between on-year and off-year flowering and the degeneration of flower forms. Ideally, fertiliser is applied three times per year. Flower fertiliser, organic fertiliser with nitrogen and phosphorus, when soil thaws' and shoots germinate aids the growth of branches and leaves and the rapid development of flower buds. This application of fertiliser is half the total yearly quantity. Shoot fertiliser, a rapid-effect compound fertiliser, is applied after flowers fade. It serves to replenish plant nutrient already consumed to maintain growth and to promote smooth new flower bud differentiation. The third application, a surface mulch to preserve soil moisture, is applied with irrigation before winter and freezing begin. The use of decomposed manure or dung at this time as the mulch ensures a safe winter and provides nutrients for the next spring. At any other time, except high summer, light liquid compound fertiliser application with watering will help better plant development if necessary.

4. Pruning

Pruning or trimming affects plant growth, flower quality, visual effect and life span. The timely elimination of dry, sick or pest-damaged branches and of redundant branches and buds can maintain the dynamic balance between the parts of the plant above ground and below ground, and the even distribution of branches. It also ensures good ventilation and illumination.

(1) Selection and Maintenance of Stems and Branches After peonies

are planted out, many new shoots appear at the collar in the first year of growth. When they develop to 10cm in the second year, those that grow healthy and are evenly distributed are kept to provide new stems and branches, and the others removed, to ensure an elegant shape. In later years, one or two new shoots are left every one or two years so that the plant becomes larger and gradually fuller as desired.

(2) Utilisation of New Shoots To develop flowers of huge size and bright colour, bud thinning should be carried out at the same time as pruning. Only one healthy and strong shoot is kept on each branch. Adventitious buds on old branches should be completely removed to concentrate nutrient for the flowers. On vigorous varieties more buds can be retained to increase the number of flowers and to prolong the flowering period. In addition, faded flowers where the seed is not required should be removed. The dried tips of branches should be removed before winter or in early spring.

5. Disease and Pest Control

(1) Peony Grey Mould (Botrytis)

This is a serious fungal disease of peonies in all countries and can occur at any time. Stems, leaves and flowers can be affected. When a young plant is infected, wet brown scabs and rot are seen at the base, then growth stops and the plant withers. When infection occurs on leaves, wet-looking spots appear at the edges. Most are brown, some purplish-brown, occasionally with irregular wheel patterns. A film of grey mould is produced on sick areas in wet weather. On petioles and stems, scabs are always dark brown strips and slightly sunken. The diseased part usually rots. Infected flower buds turn brown and dry, and rot. Low temperature and humidity in June and July, dense clusters of foliage and flowers, and excessive nitrogen fertiliser encourage the disease.

Prevention and control:

a. Sick and withered branches and fallen leaves in autumn,diseased buds and leaves in spring, are removed and deeply buried or burnt,

b. Spraying two or three times, at 10 - 15 day intervals, with 1% Bordeaux mixture with equal amounts of lime and chalcanthite, or 70% thiophanate methyl solution 1 000 times diluted, or 65% zineb solution 500 times diluted, or 50% botran 1 000 tunes diluted, is an appropriate treatment,

c. Preventive measures include proper planting density, good drainage, crop rotation in seriously affected areas, and soaking young plants for 10 -15 minutes in a fungicide before planting.

(2) Peony Brown Blotch (or Red Blotch) This is also a fungal disease which occurs in all countries. It affects the leaves, sometimes branches, floral organs and seeds. At the onset, small brown nearly circular spots appear on leaves, and expand into circular or irregular large brown spots on both sides. In serious cases, the blotches merge and the leaves become withered and twisted. In wet conditions, the backs of the blotches are covered with a dark-green film of mould. On infected stems or petioles, the infection appears in strips. The purplish-brown blotches are initially slightly convex and then concave, and later the centre splits. When the disease takes hold at the base of a branch, the branch is liable to break. Small brown spots can be seen on flower organs, and the edges of petals appear burnt, when the infection is heavy. This disease reaches its height from May to July, particularly in a warm and rainy summer. Not removing sick and damaged plants, excessive application of nitrogen, high planting density, poor ventilation and excessive exposure to sunshine encourage the disease.

Prevention and control:

a.Removal of infected parts, and thorough removal of infected plants in autumn. Before growth begins in early spring, spray with lime sulphur or 50% carbendazim 600 times diluted,

b. During the growing season, spraying 3 or 4 times, at 7 - 10 day intervals, with 50% carbendazim diluted 1 000 times, or 65% zineb diluted 500 times, is an appropriate treatment.

(3) Peony Anthracnose This disease damages leaves.stems and floral organs of a peony. In the area around Beijing, small brown spots appearing in June expend gradually into approximately circular scabs with a diameter between 4-25mm in accordance with different varieties. Along leaf edges the scabs are shaped like semi-oval. Because of the blockage from the main leaf veins ,the expanded scabs slways show a semi-oval shape as well. The colour is blackish-brown and then become gray white in the center and reddish brown around the rim. Many tiny black spots scattered in the scabs. In moist condition reddish brown gloeospore groups which is the typically features of anthracnose pro-duced. During the later period the sick scabs split and perforate. While long scabs with a diamond shape of 3-6nun can be seen from stems and petioles. They show reddish-brown, but grayish-brown with a reddish-brown fringe at last. Sick stems are often twisted and even broken. Twiggeries in morbidity die very quickly. If a perula or a petal is infected, the bud will wither up soon and the corolla will deform. The disease is still caused by mycotic infection. The infection appears in June and reaches its height from August to September in Beijing area. Heat, moist and high plant density encourage the disease.

Preventions and control:

a.Removal of infected parts (see Peony brown blotch),

b. During the growing season, spraying 2 or 3 times, at 10-15 day intervals, with 70% paroxysm, 1% Bordeaux mixture with 1:1 lime and chalcanthite.or 65% zineb diluted 500 times as soon as infection appears.

(4) Peony Zonate Spot or White Star Disease This fungal disease mainly damages peony leaves, and causes them to wither. Tiny light yellow spots appear on leaves and gradually become larger, approximately circular, 3 - 10mm in diameter, and light to mid-brown. Later, the centre of the spots turns brownish-grey and there are very obvious circular brown scabs on either side of the leaves, with fine mildew concentrated at then-centre. At leaf edges and near main veins the spots are semi-circular. In serious cases, 20 - 30 spots may be present on one leaf.

In Beijing the disease starts in June and reaches its height in August and September. It is mainly a disease of older peonies, and occurs when plants are unhealthy, or there is excessive rain and moisture, or too great planting density, or bad drainage and waterlogging, or a lack of good ventilation and sunlight.

Prevention and control:

a. Remove infected and fallen leaves and spray with 3% lime sulphur during dormancy.

b.During the growing season, spray two or three times at 10 - 15 day intervals with 1% Bordeaux mixture, or 50% Tuzet diluted 800 times, or 65% zineb diluted 500 times;

c. Preventive measures include proper planting density and good ventilation and sunlight.

(5) Peony Leaf Blight This is another fungal disease known in China and also reported in the former Soviet Union and Japan. It infects only leaves and causes early leaf fall. Initially, tiny brown spots appear on leaves. They expand to form circular scabs 1 - 3mm in diameter which are yellowish-brown and brown and slightly depressed on the surface, but dark brown at the back with a red fringe. Black grains, the pycnidia of the organism, are scattered on the scabs. Later the scabs drop leaving a perforation.

Prevention and control are the same as for brown blotch.

(6) Peony Branch-Rot This is a fungal infection that infects stems and branches. The symptoms are light brown scabs on stems, later becoming

oval and reddish-brown. When they completely encircle a stem, the stem and branches above will soon die. In autumn, black grains, the pycnidia of the organism, appear on the scabs. Infected buds turn brown and remain on the plant where they rot and die. Pathogens infect mainly through wounds. Cuts and weak plant growth facilitate the disease.

Prevention and control: Strong growth and few wounds improve resistance to the disease. Chemical treatment is the same as for Peony Zonate Spot.

(7) Peony Root-Knob Nematodes This disease, caused by northern root-knob nematodes, is known in China and other countries. In the last ten years in China this has been the most serious disease to affect root systems. It causes leaves to fall early.

The root-knob nematodes only damage nutritive roots. The first sign of the disease generally appears after flowering when the leaves turn yellow at the edges, wither and fall early. Plant growth is stunted if the infection continues for several years. Meanwhile on nutritive peony roots knobs of different sizes form. The young knobs are yellowish-white, hard and tough, and 2 - 3mm in diameter. Later on, the epidermis tissues on the knob break. When cut open, shiny white spots can be seen. The disease is characterised by 200 - 300g dense clusters of fibrous roots with knobs developing on them. The eggs and larvae of the nematodes spend the winter in knobs on the roots, or in the soil, or on wild host plants. In the spring the larvae directly infect newly developed nutritive peony roots. The nematodes are spread by movement of soil, flowing water, /on cultivation tools and by transplanting seedlings.

The periods when the infection is at its height in the Beijing area, ie May to June and October, correspond to the two dominant periods of nutritive root growth. There is evidence of a relationship between the disease and certain peony varieties. Those varieties with their roots mainly distributed to a depth of 15cm are the most vulnerable. The nematodes enjoy a wide range of hosts, and also damage many other plants.

Prevention and control:

a. Attention to plant quarantine to prevent the expansion of infected areas. Treatment of infected seedlings consists of soaking for 30 minutes either in 0.1% formaldehyde or in water at 48 - 49 °C.

b. A chemical preventive measure in the field is the insertion of granules of 15% aldicarb at a depth of about 10cm annually (at the beginning of May in Beijing).

c. Infected soil is treated by drying (0.17% moisture) and high temperature sterilisation, or by pesticides. These include methyl bromide, aldicarb and fenamiphos.