Propagation

Methods for the propagation of peonies include division, grafting, seed, layering and cuttings. The first three are those most frequently used.

1. Division

A simple method with a high survival rate and vigorous new plants. Although after division the new plants flower early, it takes two to three years before they completely show their cultivar characteristics. This method of clonal propagation directly maintains me advantageous features of the cultivar but the rate of propagation is relatively low.

(1) Division Time Division is carried out mainly in autumn. It is sometimes continued in spring after an early winter.

(2) Division Method A healthy plant 4 to 5 or more years old is dug up and the soil at its roots removed. After observing the structure of its branches, buds and root system, and following its natural growth lines, it may be broken into smaller plants, taking care not to damage twigs and buds. If the base at ground level is very compact, a knife or a pair of secateurs, or even a small saw, can be used to cut it, taking care to keep wounds as small as possible,for more rapid healing. The number of pieces obtained depends on the size and the manner of growth of the root system. Generally, 2 or more divisions can be removed from a stock plant without digging it up, by excavating soil around the roots and breaking pieces off. After division, pruning should be carried out according to the growth of new shoots at or below ground level. If there are no such shoots, one or two adventitious buds or axillary buds on the lower part of branches should be maintained and the top parts of the branches, more than 40 - 50cm above the root, cut off. If there are two or three new shoots, the top of the plant can be cut off 3 - 5cm above ground level. Broken and diseased parts of the old roots should be removed. It is better to remove old roots if there are plenty of new roots. If there are not enough new roots, healthy older roots should be kept. To discourage pathogenic bacteria, 1% copper sulphate or other appropriate prophylactic can be used to sterilise the wounds before planting.

2.Grafting

By this method, the characteristics of the cultivar to be propagated are exactly maintained at a low cost and at a high propagation rate. It is particularly appropriate for propagating cultivars with slow growth rate or which are especially rare. It is also feasible for producing "assorted" plants, ie several cultivars grafted onto one root stock, to produce, in the eyes of some people, a plant of increased value. It can also be used to regularise heteromorphosis of branches or buds, effectively creating an improved cultivar.

(1) Root Grafting This can be carried out from the last few days of August until the soil is frozen in winter. The roots of tree or herbaceous peonies can be used as root stock. Since herbaceous peony roots are short and thick, and their xylem is soft, it is an easy method to implement and the survival rate is high. Also, the growth of such grafts is vigorous, so this method is frequently used. A mature herbaceous root tuber without diseases and pests about 25cm long and 1.5 - 2cm in diameter is selected. After being allowed to dry for two to three days, the loss of water makes the tuber become soft and the operation is facilitated.

Healthy annual shoots 5 - 10cm long without diseases and pests are used as scions. If there are not enough such shoots, older twigs can be used but the survival rate is lower and the root growth slower. The scions should be conjoined immediately after cutting.

Notch grafting or cleft grafting is used. A wedge 2 - 3cm long with opposite faces at an acute angle laterally is cut at both sides of an axillary bud at the scion base. Then the top of the root stock tuber is cut off smoothly and a longitudinal cut is made. The length of this cut should be slightly greater than the scion wedge, and it should reach the centre of the tuber, so that it can contain the scion wedge. Both the cut surfaces of the stock and the scion must be flat. The bottom of the scion is inserted in the top of the stock cut and the scion pushed down into the root stock so that the cambium layers exactly touch. The two are tied together with flax and sealed with mud or liquid wax. Then the graft can be planted or heeled in.

Thoroughly dug and manured soil is prepared and levelled. The grafts are planted in rows with the terminal buds of the scion about 3cm above the soil surface after the soil is compacted. Then the grafts are completely buried by loose soil to form a roof-shaped bank for winter protection. Part of the bank is removed the following March, leaving 1 to 2cm of soil for young shoots to come through. They are watered as necessary and weeded. The bank should be maintained so that roots can be produced from the join. In early April flower buds are removed so that all nutrient can be used for young shoot growth. Branches at the top above the bank should be removed from the year-old graft towards the end of September to encourage more branches so that more roots will grow the next year.

In the second year, fertiliser is applied in early March, early May and late August, and the soil is irrigated as necessary. Diseases and insect pests should be controlled. After two years grafts can be transplanted towards the end of September. The herbaceous peony root stock is completely cut off if sufficient root has grown from the scion, but only a half or one-third removed if there are few or even no new scion roots.

(2) Scion Grafting

a. Base Grafting: This is carried out just above ground level. The best time is towards the end of September. Seedling tree peonies are used as root stock and cut across 5cm above ground. The current year's healthy base shoots are selected as scions. An oblique wedge about 3cm long is cut at both sides of an axillary bud at the base of the scion. The stock is split to a depth of about 3cm and the scion is inserted into the root stock so that the cambium of scion and root stock are in contact. The graft is bound firmly with flax or plastic tape. The scion is covered by earthing up for winter protection and other management methods are the same as those for root grafting.

b. Side Grafting: This method is frequently used for grafting at a higher position on a plant to effectively change a cultivar or to cultivate a plant bearing flowers of different colours. It is carried out between mid-July and mid-August. A tree peony is used as the root stock. Healthy basal shoots from selected cultivars are used as scions and one or two leaves are retained. At the back of the scion at a bottom bud, a diagonal cut about 1.5 - 2cm long is made. Then on the other side a wedge 0.3 - 0.5cm long is made with another sloping cut. Next, on the smooth part at the base of a current year's twig with one or two buds, a diagonal cut of 1.5 - 2cm is made to reach one-third to one-half the depth of the branch. The scion .is immediately fitted into this cut on the stock with the cambium of stock and scion in contact, and flax string is used to bind them together. Above the graft, one-third to a half of the stock branch, should be removed at once in order not to tear the union through excessive weight. When the budded scion is seen to be surviving, any auxiliary buds on the stock are removed to ensure maximum nutrient supply for the scion. The string bound around the cuts is not released until the two parts are firmly united. Then the remaining part of the stock and any bottom buds are removed and some additional manure is spread to help growth. While the side graft is becoming established on the stock branch, it is best to keep the stock plant shaded to prevent excessive transpiration.

(3) Bud Grafting Bud grafting can be carried out between April and August when the bark and phloem of branches can be peeled off. However, the survival rate is greatest if it is done during May, June and early July. All tree peonies can be used as stock. Plump buds from the current year's growth are selected as scion material. Buds from 2- to 3-year-old branches can be used if budding is done during April and May.

Two cuts are made 1.2-1.5cm above and below the selected bud. The width of the bud piece is generally half that of the scion with minimum width at least 0.5cm. The bud is taken off with part of the xylem, and any leaves are immediately removed. Then a cut slightly smaller than the bud piece is made at an axillary bud at the grafting location on the stock. The bud piece is gently peeled with a grafting knife leaving the wooden bud knob. Then the xylem of the stock is lifted with the tip of the knife and the bud piece with the bud knob is swiftly embedded into the stock cut. The scion bark around the bud piece is trimmed if necessary and plastic tape is used to seal the cuts tightly, with only the bud piece and petiole left outside.

If a bud piece is grafted onto a 2- to 3-year-old branch, a cut the size of the bud piece is made in the stock and the stock bark is lifted up. The bud piece is quickly put into the stock cut and then is tightly tied up. All leaves, with their petioles, on the stock above the bud piece are removed but those below the bud piece are retained. The success of the graft can be determined 10-15 days after grafting. If the grafted bud is fresh and swelling, it is alive, and excessively tight binding should be loosened. If the graft has failed, a replacement should be made. Before sprouting in the following year, the stock 1cm above the bud is cutoff after the bud begins to develop. Basal shoots are removed.

3. Propagation from Seed

This is mainly used for large scale production of root stock for grafting; also of course to obtain new cultivars.

Tree peony seeds begin to ripen in late August. The complete seed heads can be harvested when their skins turn brownish-yellow. The seed heads are spread out to mature and dry in a cool and well-ventilated place, possibly indoors. When the seed skins become black and the follicles crack naturally, the seeds can be removed, and after another two or three days for drying, they can be sown. Sowing is best begun in early September for a high germination rate. To stimulate early germination, the seeds are placed in wet sand. After two months young roots are produced and the seeds are then sown in earth. If seeds are very dry at the time of sowing, they can be soaked in warm water for 24 hours. Soaking in sulphuric acid for 2 to 3 minutes, or in 95% ethyl alcohol for 30 minutes, are also helpful.

Sandy soil is chosen for seedling cultivation, and free-draining and approximately neutral soil is recommended; also it should be well fertilised. According to experience in Heze, 30 - 45 tonnes of manure or 6 -7.5 tonnes of eake fertiliser per hectare is appropriate. If the soil is very dry, irrigation and the addition of organic matter for water retention is needed before deep digging and leveling.

Sowing in rows is usual but seed is also broadcast. About 150 kg of seed is used per hectare, and covered with 2 to 3cm of fine moist soil.

Tree peony seeds revert to a dormant state after germination, and only roots develop in the first year. If seeds are soaked in 0.6 - 1.0 mL per litre gibberellin for 24 hours before sowing, or if after root development gibberellin is watered in once or twice per day, the dormancy can be broken after one week.

4. Layering

(1) Ground Layering This method is useful for varieties with few basal shoots or a less developed root system, but the rate of production of new plants is low.

Layering is done at the end of May and beginning of June after flowering. A strong and healthy two- to three-year-old branch is selected and pressed down. It is notched at the junction of the current year's growth and the older part of the branch. It is laid in the earth and fixed, usually with weights. The soil should be kept moist for new roots to germinate. It is more beneficial for new root development if the part of the old branch not pressed into the earth is also notched nearly to breaking but still connected. When sufficient fibrous roots grow, the rooted branch can be cut away from its parent tree and it becomes an established new plant before the next winter.

(2) Air Layering The success rate of air layering is highest when it is carried out ten days after flowering, when the branch is half lignified. A girdling cut with a width of 1.5cm is made about-1cm below the second or third leaf axils at the base of the twig. Then absorbent cotton dipped in 0.5 -0.7mL per 10 litres indolebutyric acid or 0.4 - 0.6mL per 10 litres solution of hormone rooting powder is placed and secured around the root producing area above the upper part of the girdle.

Plastic film is tied round this and then cut to form a cylinder. A wet and loose mixture of ground slag and moss mixed with clear water is fed into the cylinder, which is then sealed and supported by poles. Immediately after the "bag" is suspended, 30mL of clean water is injected, and then 30 - 50mL of water is given every 15-20 days. When roots germinate, after one-and-a-half to two months, liquid nutrient is supplied instead of water. When the new young roots can be seen, the branch can be cut from the parent plant and transplanted into a pot or a nursery bed for further cultivation and care. The success rate can reach 70% or more.

5. Cuttings

Although peonies can be propagated by cuttings, the slow growth and difficulty of maintaining the precise care needed mean that this method is rarely adopted for production. Cuttings are taken in September. Current year's growth of 15 - 20cm long with 2 - 3 buds is used for cuttings. On planting cuttings, shading and control of moisture are needed. Roots can appear after 20 - 30 days. Cuttings can be treated with 0.5mL per litre naphtha-leneacetic acid, or 0.3mL per litre indolebutyric acid, or 0.5 - l.OmL per litre gibberellin, to stimulate root production.

In order to increase the survival rate of planted cuttings, ridging can be carried out in late autumn or spring.

6. Double Levelling Method

This is a new technique for rapid peony production. The advantages include convenience and ease, saving of labour and time, high production rate, and rapid new plant growth in large quantities and at a uniform pace. It can also be applied widely.

This method of propagation can be used at any time during the dormancy period, but is best done in September and October. A parent plant is dug up and divided immediately into smaller plants, each with one or two branches. Then these plants are planted in holes of 30 - 35cm in depth, 25 - 30cm in diameter and 70cm apart in prepared ground. On one side of the holes, the location for level underground layering, a hole 20cm wide, 10cm deep and the same length as the branches is excavated for the branches to be pressed into the soil when two-thirds of the base of the plant is covered. The tips of the branches should be lower than or at the earth surface while the lower part of the branch is buried slightly deeper. When covered by soil, perhaps in ridges, and compacted, the buried plants are thoroughly watered. Manure should be

dug in before planting, and top-dressing fertilisers should be heavily applied during growth. If the apical buds grow normally in the first spring after branch burying, the developed branches can be cut during September and October. Because the apical dominance is eliminated when the branches are buried, many lateral buds develop in the next spring. The new branches that develop are pressed into the ground in September or October of the same year so that even more shoots come from the buried branches. In the third autumn the whole plant is dug out and divided into several new small plants according to the root development from the buried branches and the branches above the ground. Generally, a parent buried branch can form eight to ten new young plants.