Cultivation Methods and Key Technical Points for Plum Bonsai
Plums are deeply loved for their brilliant and varied forms and colors and their rich, fragrant fruit aroma. Plum bonsai is popular because it offers both flowers and fruit.
Selection of rootstock and varieties
Choose dwarf rootstocks with strong compatibility with the grafted variety, and prefer varieties with bright fruit color, high yield, and slightly weak growth vigor. Plums have very rich variety diversity. Traditional excellent varieties in China include "Furen Li, Jiaqing Li, Xieli Li, Hongxiang Li, Yuhuang Li, Mi Li, Wuyue Li," and others. At present, the main domestic and introduced foreign plum varieties promoted and applied in production include: Oishi Wase, Japanese Plum King, Methley, Rose Queen, Black Gem, American Large Plum, Changle Niuxin Li, Xianfeng Li, and others.
Potting soil preparation
Because the container of plum bonsai is limited, the limited potting soil must contain sufficient fertility to maintain the needs of plum growth and fruiting. Generally, mix 4 parts rotted leaves, 2 parts decomposed barnyard manure and crushed bone, and 4 parts garden soil, and appropriately mix in a small amount of superphosphate, diammonium phosphate, etc., to increase soil fertility. Mix the potting soil thoroughly, crush it finely, and sieve it. Before use, the culture soil should be sprinkled with 1.5% formalin solution for disinfection. When planting, let the root system spread out, firm the soil by pressing, and follow the practice of "three burials, two pressings, and one lifting of the seedling," water thoroughly with bottom water, and place in a cool place to recover.
Fertilizer and water management
The organic fertilizer in the potting soil of plum bonsai is far from sufficient to meet its growth and development needs, so fertilizer and water management must be strengthened during the growing season. Fertilization should be mainly organic fertilizer, with rational application of chemical fertilizers. When potting, mix in decomposed organic fertilizer; before bud break or before flowering, apply 1 application of quick-acting nitrogen fertilizer, watering about 1 kilogram of fertilizer water per plant, to promote neat bud break and flowering. At the end of the full bloom stage, carry out foliar topdressing, using 0.3% urea or 0.2% monopotassium phosphate, spraying once every 10 to 15 days, for 2 to 3 consecutive sprays, to promote young fruit enlargement and accelerate new shoot growth. Late June to early July is the period of flower bud differentiation. Thin fertilizer water may be applied (such as well-rotted soybean cake fertilizer water, sesame paste residue water, or human waste, etc.), once about every 10 days, for 2 to 3 consecutive times, to promote flower bud differentiation and increase the fruit-setting rate. In August to September, during vigorous growth, to control new shoot growth, stop using nitrogen fertilizers (such as urea, ammonium sulfate, ammonium bicarbonate, etc.), and focus on phosphorus and potassium fertilizers (such as monopotassium phosphate or plant ash, etc.), applying thin fertilizer frequently. The water for plum bonsai should be properly controlled. A thorough watering must be guaranteed once a day, and watering should be done in the morning and evening, avoiding watering at high-noon temperatures. Grasp the principle of "do not water if not dry; when watering, water thoroughly." In high-temperature seasons, foliar misting may be carried out to increase air humidity and lower leaf temperature. After leaf fall, apply decomposed organic fertilizer. During dormancy, watering must be strictly controlled, to the extent that the potting soil is not overly dry.
Repotting and soil replacement
The nutrients in the potting soil are gradually leached away by frequent watering. After 2 to 3 years, the fertility in the potting soil is insufficient and the physical structure deteriorates, so the pot must be changed in time and new culture soil added. Stop watering before repotting, so that the soil shrinks and separates from the pot wall, making it easier to remove the potting soil. After turning the root ball out upside down, cut away old roots 2 to 3 cm thick around the potting soil, mix organic fertilizer and soil evenly, sieve, and fill the bottom. Then repot with the root ball, add fertile soil around it, and water thoroughly once. Because the root system of plum bonsai grows quickly, after 1 to 2 years the roots grow curled along the pot wall, becoming tangled and densely packed with old roots, which affects the growth of new roots. Therefore, when changing pots, cut the curled root system and thin out the old roots that are too crowded, which is beneficial to new root growth and improves the ability to absorb water and nutrients.
Shaping and pruning
The tree form of plum bonsai should not only favor fruiting but also have an aesthetic effect and enhance its ornamental value. Usually the natural round-headed form and tower form are the main ones, and according to personal preference it may also be shaped into favorite tree forms such as cascade style, curved-trunk style, and others. After potting, in 1 to 2 years, measures such as propping, pulling, and bending should be fully used to open the angle of branches, so as to bear fruit earlier.
When pruning, focus on moderate heading back of one-year-old branches to stimulate branch sprouting and form a compact small-canopy tree form for fruiting. For young plum trees, while selecting and retaining and cultivating good main and secondary branches and completing the shaping task, balance the tree vigor and maintain the leader-follower relationship among trunk and scaffold branches at all levels; appropriately prune scaffold branches that are too vigorous. For trees beginning to bear fruit, fruiting is mainly on short fruit branches and bouquet-like fruit spurs. After entering fruiting, according to the strength of growth, heavy pruning may be done by retaining 2 to 3 plump buds at the base. Overlong branches may be reduced to the two-year-old branch position, so that the medium and small branch groups within the whole canopy are distributed compactly.
Winter protection against cold
When no freezing injury occurs in winter, it is generally not suitable to overwinter indoors. Let it overwinter and go dormant naturally outdoors, to improve the tree's ability to resist various natural disasters. To prevent freezing injury, choose clear weather and water thoroughly once before the soil freezes. After the water seeps down, wrap the entire container with straw bags and tie them tightly with rope. It may also be buried in a trench in a wind-protected, sunny place.
Pest and disease control
The main pests of plums include fruit borers, red spider mites, leaf rollers, slug moths, and others. For pest outbreaks, spray 1000 times dilution of fenitrothion or 1500 times dilution of 40% dimethoate for control. The main diseases include bacterial shot hole disease, ring rot, brown spot, and powdery mildew. For diseases, use 0.5% lime double-strength Bordeaux mixture, spraying once in late April or early May, and then spraying 2 to 3 more times every half month. For bacterial shot hole disease, spray leaves with 3000 times dilution of 72% agricultural streptomycin soluble powder.