What are the latest propagation methods for tree peonies?

Tree peonies can be propagated by sowing, division, or grafting. Division and grafting are the methods most commonly used, and sowing and cuttings can also be used. The suitable time for transplanting is from late September to early October, and it should not be done too early or too late. The sowing method is mostly used for breeding new cultivars.

Division propagation

The division propagation of tree peonies was already widely used in the Ming Dynasty. The specific method is as follows: dig up an entire large, vigorously growing tree peony and separate it at the points where the root system naturally joins. The number of daughter plants divided from each plant depends on the size of the original plant; large ones are divided into more, and small ones can be divided into fewer. Generally, every 3-4 branches form one daughter plant, and it should have a relatively complete root system. Then mix a small amount of sulfur powder with mud. Apply the mixture to the wounds on the roots and rub it evenly, and then it can be planted elsewhere. The time for division propagation is during the period from the Autumnal Equinox to Frost's Descent each year, and it is best done at the proper time. At this time, the air temperature and soil temperature are relatively high, and the tree peony is in a semi-dormant state, but there is still a fairly long period of vegetative growth, so carrying out division and planting has little serious effect on root growth, and after division and planting some new roots and a small number of shoot buds can still be produced. If division and planting are too late, root growth in that year will be very weak, or no new roots will form, and in the following spring the plant will develop even more weakly; weak roots cannot tolerate drought and the plant is likely to die. If division is too early, when the air temperature and soil temperature are relatively high, it can still grow rapidly, which easily causes autumn growth. The mother plant used for division of tree peonies is generally a robust clump. The mother plant used for division propagation should retain as many root suckers as possible, and all the roots on the new seedlings should be retained so that after 5 years of growth more new seedlings can be divided from them. Such plants are easy to establish after planting and also grow more vigorously. The more roots retained, the more vigorous the growth.

Grafting propagation

The grafting propagation of tree peonies is divided into two types according to the rootstock used: one is wild tree peony; the other is using herbaceous peony roots. The commonly used grafting methods for tree peonies mainly include three: inlay grafting, side grafting, and bud grafting. Inlay grafting uses herbaceous peony roots as the rootstock; because herbaceous peony roots are soft and have no hard core, they are easy to graft, and the roots are thick and short with sufficient nutrients, so after the graft takes, early growth is vigorous. If tree peony roots are used for grafting, the xylem is harder and grafting is more difficult, but the lifespan is longer. The best time for grafting is generally from late September to early October each year. The rootstock used is a robust herbaceous peony root 2-3 cm in diameter and 10-15 cm long, free of pests and diseases. Side grafting is a method of high grafting to change the top and improve cultivars; it uses the many branches on inferior tree peonies or 8-10-year-old medicinal tree peony plants and grafts them into superior cultivars of different colors. The grafting time is from early July to mid-August. First select a tree peony plant with superior cultivar characteristics, robust growth, and no pests or diseases, and cut from it soil shoots emerging from the ground, or short branches of the current year 5-7 cm long; it is best to use short branches with 2-3 strong buds as scions. Keep one leaf stalk on the scion. After selecting the scion, make a slanted cut on the back side of the lower bud of the scion in the shape of a horse's ear, then make another slanted cut on the other side of the horse's-ear shape into a wedge shape, so that after grafting both sides can come into contact with the cambium tissue between the xylem and phloem, which makes it easier to survive. Before and after side grafting of tree peonies, except that no irrigation is given during the rainy season, suitable moisture for normal plant growth should be maintained. Bud grafting is an effective method for propagating tree peonies and cultivating multiple cultivars and multiple flower colors on one plant. The time for bud grafting is from May to July. It is best to do the grafting on sunny days. The methods include the bark patch method and the bud replacement method. The bark patch method is to cut out a rectangular or shield-shaped incision together with the xylem on the current-year branch of the rootstock, then cut off the axillary bud of the scion together with the xylem into a bud piece the same size and shape as that on the rootstock. Then quickly press the bud piece onto the incision on the rootstock and tie it tightly with plastic string. The bud replacement method is to remove the axillary bud together with the cambium at the grafting site on the rootstock, keeping the intact bud embryo on the xylem, then in the same way peel off the axillary bud of the scion, quickly fit it onto the bud embryo of the rootstock, taking care that the two match, and finally tie it tightly with plastic string. After grafting, the plants should be watered, the soil loosened, and fertilizer applied in time to promote healing.

Cuttings propagation

Cuttings propagation is a method of using tree peony branches, which readily produce adventitious roots, to propagate new plants, and it is one of the asexual propagation methods. The method is to first cut off the branch to be used as a cutting, detach it from the mother plant, and then insert it into soil or another substrate so that it roots and becomes a new plant. For the branches used in tree peony cuttings propagation, choose current-year soil shoots emerging from the base of the tree peony, or when pruning and shaping the tree peony, choose branches with solid stems, plump terminal buds, and no pests or diseases as cuttings, 10-18 cm long. The roots of tree peonies are fleshy roots, prefer dryness, avoid moisture, and tolerate drought. Therefore, the nursery bed should be chosen in a ventilated, sunny place and built as a raised bed for raising seedlings. When cutting, after finishing one bed, water that bed, giving one thorough watering.

Seed propagation

Seed propagation is the use of seeds to reproduce offspring or select and breed new cultivars, and it is a sexual propagation method. Before sowing, the soil must be rather carefully prepared and disinfected, the land must be deeply plowed and finely worked, and sufficient base fertilizer must be applied. Then build small beds 70-80 cm wide, and either hole sowing or drill sowing may be used. Sowing should not be too deep, with 3-4 cm as the limit, and after sowing cover with soil level with the bed surface. Then gently firm the soil and immediately water thoroughly.

Layering propagation

The layering method for tree peonies is a propagation method based on the principle that branches can produce adventitious roots. The branch is bent down or buried with soil on the plant without being detached from the mother plant, the soil is kept moist, the buried part of the branch roots, and then it is cut off and planted to become a new plant. It is likewise an asexual propagation method for tree peonies. This method mainly includes: the pot-nesting and soil-mounding layering method and the double-flat method.

Tissue culture

Plant tissue culture propagation is based on the totipotency of plant tissue cells and uses tree peony embryos, flower buds, stem tips, young leaves, and leaf stalks for in vitro culture. Generally, these materials are placed in 75% alcohol and soaked for 5-10 minutes, then immediately put into sterile water for washing, then soaked in a 5% Antiformin solution for 7-10 minutes for surface sterilization, then rinsed 3-4 times with sterile water, and finally placed on culture medium for aseptic culture. The basic culture medium is MS, and the other additional components mainly include: different concentrations or different combinations of indoleacetic acid, naphthaleneacetic acid, indolebutyric acid, gibberellin, hydrolyzed protein, and so on.