Detailed Explanation of the Key Cultivation and Management Techniques for Magnolia denudata

Yulan, also known as white magnolia, Yutangchun, or wood flower tree, is a deciduous tree of the genus Magnolia in the family Magnoliaceae. It is native to Anhui, Zhejiang, Hunan, Hubei, Guizhou, Guangdong, Shanxi and other regions, and is also widely cultivated in Beijing and areas to the south. The flowers of Yulan are pure white, large and fragrant, making it an important early-spring flowering tree species in gardens, and it is deeply loved by people. When planted together with crabapple, winter jasmine, tree peony and osmanthus, it carries the meaning of good fortune and prosperity, and has the elegant name "Yutang spring wealth and honor." The cultivation and management techniques for Yulan are introduced below for reference only.

I. Common ornamental tree species in the same genus

The genus Magnolia in the family Magnoliaceae has about 90 species, with about 30 in China. Common species and cultivars in gardens include: yellow magnolia (Magnolia denudata cv. Feihuang), purple magnolia (Magnolia liliflora Desr), Wangchun magnolia (Magnolia biondii Pamp), Erqiao magnolia (Magnolia x soulangeana (Lindl.) Soul.-Bod.), purple-flowered Yulan (Magnolia denudata var. purpurascens Rehd. et Wils), and so on.

II. Selection of the planting environment

Yulan likes light. Young trees are relatively shade-tolerant and are not tolerant of strong light or afternoon western sun; overly strong light or western exposure can easily scorch the trees. Yulan can be planted in an environment with lateral shading; if planted under large trees or in shady spots, it grows poorly, with a thin and small tree form, sparse branches, small and yellowing leaves, and no flowers or only small flowers. Yulan is relatively cold-hardy and can withstand a brief low temperature of -20°C, but it should not be planted in wind gaps, otherwise shoot dieback is likely to occur. In Beijing, in a wind-sheltered, sunny location, it can overwinter safely in the open ground without measures such as wrapping the trunk. Yulan prefers fertile, moist, well-drained slightly acidic soil, but can also grow normally in mildly saline-alkaline soil (pH 8.2, salt content 0.2%). Yulan has fleshy roots and fears waterlogging, so the planting site should be elevated; planting in low-lying areas can easily cause root rot and death. The soil at the planting site should also have good permeability; planting in clay leads to poor growth, while it grows best in sandy loam and yellow sandy soil.

III. Digging up and planting of seedlings

Yulan does not transplant easily. Generally, transplanting 10 to 15 days before bud break, or when the flowers have just faded but the leaves have not yet unfolded, is ideal. Four to five days before digging up the seedling, water it thoroughly once. This not only allows the plant to absorb sufficient water, which helps survival after planting, but also helps the soil form a ball when digging. When digging, damage the root system as little as possible, and the wounds on broken roots must be smooth to facilitate healing. In addition, it should be noted that no matter what size the seedling is, it should be dug with a soil ball, and the diameter of the soil ball should be 8 to 10 times the ground diameter of the seedling. It must not be too small, because if it is too small it will not protect the root system. After the soil ball is dug, it should be tied well with straw rope to prevent it from breaking apart during transport.

Before planting, dig the tree pit well. The tree pit should be large rather than small; if the tree pit is too small, it is not only troublesome to plant but also unfavorable for root growth. The subsoil at the bottom of the tree pit is best if it is matured soil. If the soil is too clayey or the pH value or salt content exceeds the standard, foreign soil should be used or the soil should be improved. The cultivation soil must have good permeability and sufficient fertility, must be able to supply the plant with enough nutrients, and must not contain impurities such as bricks, tiles or lime. The planting depth should be appropriate. Generally, the planting depth can be about 2 to 3 cm higher than the original soil ball; too deep and the buds may suffocate, too shallow and the roots will be exposed and the tree may easily be blown over by wind. Large-sized seedlings should have supports set up promptly; triangular supports can be used to prevent them from being blown askew by wind. After planting is completed, water immediately, water a second time after 3 days, and water a third time after 5 days. After the third watering, normal management can begin. If the planted seedling bears flower buds, the buds should be cut off to prevent flowering and fruiting from consuming a large amount of nutrients and affecting the survival rate.

IV. Water and fertilizer management

Yulan is neither tolerant of waterlogging nor drought. In cultivation and maintenance, the principle that it "likes moisture and fears waterlogging" should be strictly followed. In the process of cultivation and maintenance, many people believe that because Yulan fears waterlogging, it should be watered as little as possible. This understanding and practice are very wrong, because Yulan's fear of waterlogging does not mean it likes drought; it itself prefers a moist environment. In water management, one should grasp the degree of keeping the soil neither too dry nor too wet. Based on many years of cultivation practice, the author believes that during cultivation the soil should be kept moist without standing water. During maintenance, newly planted Yulan should keep the soil moist, and this is also an important measure to ensure its survival rate. For Yulan that has entered normal management, the green-up water in early spring and the antifreeze water in early winter are indispensable, and they should be watered sufficiently and thoroughly. During the growing season, water once a month; watering should stop during the rainy season, and drainage should be carried out promptly after rain to prevent root rot caused by standing water. In addition, loosening the soil to preserve moisture should also be carried out promptly. It should be noted that irrigation should also be carried out promptly during dry periods in the rainy season. Lack of water not only affects the plant's vegetative growth but can also cause flower buds to drop or shrink, affecting flowering the following year.

In addition, for Yulan planted in poor site conditions, especially in environments with a large hardened area and a small green area, under continuous high temperature and drought, foliar spraying should be carried out at the same time as root watering. Attention should be paid to the degree of atomization when spraying; the higher the degree of atomization, the better the effect. The best spraying times are before 8:00 in the morning and after 6:00 in the evening; spraying should not be done at midday when light is strong. For Yulan that has suffered waterlogging damage, rescue should be carried out immediately. First, drain the standing water promptly; second, shade the tree, especially to prevent western sun exposure; third, cut off some leaves and flower buds.

Yulan likes fertilizer. In addition to applying base fertilizer at planting, it should be fertilized every year thereafter. Sufficient fertilizer can make the plant grow vigorously, with green and thick leaves, not only producing many buds but also large flowers, a long flowering period, and rich fragrance. Fertilize Yulan 4 times each year: apply a nitrogen, phosphorus and potassium compound fertilizer once before flowering; this fertilization can not only improve flowering quality but also benefit spring growth. Apply a nitrogen fertilizer once after flowering; this fertilization can increase the plant's growth amount and expand the nutritional area. Apply a phosphorus and potassium compound fertilizer once in July and August; this fertilization can promote flower bud differentiation and increase the degree of lignification of new shoots. Before winter, in combination with watering winter water, apply a fully decomposed and fermented barnyard manure once; this fertilization can not only improve soil activity but also effectively raise soil temperature, and the amount applied should be large rather than small. In addition, for seedlings planted in the same year, if their growth is poor, a 0.2% potassium dihydrogen phosphate solution can be used for foliar spraying, which can effectively strengthen the tree's vigor.

V. Overwintering management

Although Yulan can withstand a low temperature of -20°C, small-sized Yulan and Yulan planted in the same year should have overwintering management strengthened. In addition to watering thoroughly with freezing water after leaf fall in mid-to-late November, the tree pit should also be treated with grass mulch, film mulch, or mounding with soil, and the tree body can be whitewashed to prevent spring shoot dieback. For Yulan that has survived and grown for many years, it is sufficient to only apply antifreeze water and whitewash treatment.

VI. Pest and disease control

1. Diseases. Yulan is a tree species with relatively strong disease resistance. The main diseases are anthracnose, chlorosis and leaf scorch.

(1) Anthracnose symptoms and patterns: Anthracnose mainly damages the leaves of Yulan. It mostly starts from the leaf tip or leaf margin, producing irregular lesions, or nearly circular lesions form on the leaf surface. In the early stage, the lesions are brown and water-soaked, with small black particles on the surface, and a dark brown raised line at the edge, with a clear boundary from the healthy part. The pathogen of anthracnose overwinters as mycelium on the tree body or fallen leaves. The following spring it produces conidia, which spread to the plant by wind and rain. The spores germinate in water droplets, invade leaf tissue, and cause disease. The peak incidence period is during high temperature and high humidity in summer. This disease is extremely likely to occur when water and fertilizer management are inadequate, ventilation is poor, and growth vigor declines.

Control methods: strengthen water and fertilizer management, enhance tree vigor, and improve disease resistance; promptly remove diseased leaves, and at the end of autumn remove fallen leaves and burn them in a centralized manner; if disease occurs, spray with 75% chlorothalonil wettable powder 800 times solution or 70% carbendazim-thiram 500 times solution, once every 10 days, continuously spraying 3 to 4 times to effectively control the disease. Specific-effect agents: Penjunjun, kresoxim-methyl, amisulbrom, etc., have specific effects on diseases caused by fungi.

(2) Chlorosis symptoms and patterns: it first appears as small leaves losing green, with chlorophyll gradually decreasing, and leaves turning yellow or pale yellow while the veins remain green. As the disease progresses, the entire leaf turns yellow and then gradually whitens, the plant gradually declines in growth, and eventually dies.

Control methods: chlorosis is a physiological disease, mainly caused by overly clayey soil, pH value exceeding the standard, and insufficient iron supply. A 0.2% ferrous sulfate solution can be used to drench the roots, or a 0.1% ferrous sulfate solution can be used for foliar spraying, and more farmyard manure should be applied.

(3) Leaf scorch symptoms and patterns: in the early stage, the leaves of the plant show scorched edges, after which the leaves gradually shrink and dry up. In severe cases, new leaves cannot unfold, and a large number of leaves dry up and fall off. This disease often occurs under poor site conditions, such as a large hardened area and a small green area; long periods of high temperature, drought, and overly strong light; and soil alkalization or excessive flower quantity.

Control methods: increase watering frequency and keep the soil moist; apply more organic fertilizer to strengthen tree vigor and improve plant resistance; whitewash or wrap the tree trunk.

2. Insect pests. The main pests damaging Yulan include: bagworms, Psilogramma menephron, red spider mites, longhorn beetles, etc., and occasionally underground pests such as grubs. If pests occur, 80% dichlorvos emulsifiable concentrate 800 times solution or 50% fenitrothion emulsifiable concentrate 800 times solution can be used to kill bagworms; Bt emulsion 800 times solution or 50% fenitrothion emulsifiable concentrate 800 times solution can be used to kill Psilogramma menephron; 40% dicofol 800 times solution or 5% hexythiazox 2000 times solution can be used to kill red spider mites; Green Weilei 500 times solution can be used to kill longhorn beetles; and 50% phoxim emulsion 1000 times solution can be used to drench the roots to kill grubs.

VII. Pruning and shaping

Because the branches and trunk of Yulan have relatively poor wound-healing ability, it is generally not pruned unless necessary. If the tree shape is unattractive or relatively messy, diseased and pest-infested branches, dead branches, drooping branches, water sprouts, overly dense branches, and useless branches should be thinned out to facilitate ventilation and light penetration and produce a beautiful tree shape. The pruning time is before leaf expansion in early spring. Yulan is generally not headed back, so as not to cut off flower buds. If pruning is needed, larger wounds should be coated with Bordeaux mixture to prevent pathogen infection.