Cultivation and Management Techniques for Magnolia in North China

Magnolia is a deciduous tree of the genus Magnolia in the family Magnoliaceae, native to Jiangxi, Zhejiang, Hunan and other places, and is also widely cultivated in areas south of Beijing. Magnolia has pure white flowers, large blooms and fragrant scent, and is an important early-spring flowering tree species in gardens. Its cultivation and management techniques in North China are introduced below.

Growth habits of magnolia

Magnolia prefers light and tolerates slight shade, and can be planted under conditions of lateral shading, but should not be planted under large trees or in shady spots; magnolia is relatively cold-tolerant, and in Beijing in a sheltered, sunny spot it can overwinter safely in the open without measures such as wrapping the trunk; it prefers fertile, moist, slightly acidic soil, but can also grow normally in mildly saline-alkaline soil (pH 7 to 8.2, salt content below 0.2%); magnolia has fleshy roots and fears waterlogging, so the soil at the planting site must have good permeability, with sandy loam being ideal.

Selection and planting of seedlings

The selection of seedlings directly affects the survival rate of planting and the future ornamental effect, so the selection of seedlings must be strictly controlled. Apart from the fact that the specifications of the seedlings can be determined according to greening needs, the following points should also be grasped when selecting seedlings: First, the seedlings must not have pests or diseases; when selecting seedlings, carefully inspect the tree body to see whether there are hyphae, disease spots or decay, and carefully check whether there are insect holes, live insects, eggs or cocoons; if so, try not to select them. Second, choose seedlings with a good tree shape; the main trunk of the seedling should be straight, the main branches and lateral branches should be evenly distributed, there should be no lopsided crown, and the top shoot should remain intact. Third, pay attention to checking whether the tree body has bark injuries; if there are bark injuries or splits, they will affect the transport of nutrients and water, which is not conducive to the survival of the seedling. Fourth, after selecting the seedlings, when lifting them the plant must be kept with a soil ball, and the diameter of the soil ball should be 8 to 10 times the diameter at breast height; after the soil ball is dug, it should be tied well with straw rope to prevent it from breaking apart during transport.

In order to ensure the survival rate of the seedlings, attention should also be paid to the following aspects when planting. First, the best planting time is before flowering in early spring. Second, 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 not conducive to root growth. Third, if the soil is too sticky or the pH value is too high, replacement soil should be used. Fourth, the subsoil is best if it is matured soil and should be mixed evenly with base fertilizer. Fifth, the planting depth should be appropriate; generally speaking, the planting depth of the seedling can be slightly higher than the original soil ball by 2 to 3 cm; too deep and it is prone to stifling the buds, too shallow and the roots will be exposed. Sixth, large seedlings should be staked in time to prevent them from being blown askew by the wind. Seventh, after planting is completed, the first watering should be done immediately, the second watering three days later, and the third watering five days later.

Magnolia prefers moisture and fears waterlogging, and this principle should be strictly grasped in cultivation and maintenance. However, in practice many people think that because magnolia fears waterlogging, it should be watered as little as possible. Yet it should be known that fearing waterlogging does not mean liking drought; magnolia itself likes a moist environment, so how should this balance be controlled? In the author's view, during cultivation the soil should be kept moist but not waterlogged. During maintenance, the surface soil of newly planted magnolia must be kept moist, which is also an important measure to ensure its survival rate. After entering normal management procedures, the green-up watering in early spring and the antifreeze watering in early winter are indispensable. In other seasons, whether to water can be determined according to soil moisture and rainfall conditions, and during the rainy season the soil should also be loosened in time to preserve moisture. During dry periods in the rainy season, irrigation should also be carried out in time; lack of water will not only affect vegetative growth, but can also cause flower buds to fall off or shrink. It should be mentioned that for magnolia planted in poor site conditions, especially in environments with a large hardened area and a small green area, under continuous high-temperature and droughty weather, while watering the roots, water should also be sprayed on the leaves; attention should be paid to the degree of atomization when spraying, and the higher the degree of atomization, the better the effect; the best spraying times are before 8 a.m. and after 6 p.m., and it must not be done at noon when the light is strong.

Magnolia prefers fertilizer. In addition to applying base fertilizer at planting, topdressing should be carried out every year; sufficient fertilizer can make the plant grow vigorously, with more and larger flowers and a longer flowering period. Magnolia can be fertilized 4 times a year, namely: apply a nitrogen, phosphorus and potassium compound fertilizer once before flowering; this fertilization can improve the quality of flowering and benefit spring growth. Apply a nitrogen fertilizer once after flowering; this 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 branches. Before winter, combined with watering for winter, apply a fully decomposed and fermented barnyard manure once; this fertilization can improve soil activity and can effectively raise ground temperature. In addition, for small seedlings planted in the same year, if their growth is poor, a 0.2% potassium dihydrogen phosphate solution can be applied by spraying on the leaves, which can effectively improve tree vigor.

Overwintering management

Magnolia planted in the same year should have overwintering management strengthened. In addition to timely and thorough watering of the freezing water, the tree pit should also be treated by covering with grass, covering with film or hilling up soil, and the tree body can be treated by whitewashing. For magnolia that has survived planting for many years, only antifreeze watering and whitewashing need be carried out.

Pest and disease control and pruning and shaping

Magnolia is a tree species with relatively strong resistance. Its main diseases include black spot disease, yellowing disease and leaf sunscald disease. Black spot disease is caused by infection by fungi imperfecti; if it occurs, broad-spectrum fungicides such as 70% mancozeb 500-fold solution and 75% chlorothalonil 800-fold solution can be sprayed on the leaves for control; during routine maintenance, attention should also be paid to ventilation and light transmission, and water and fertilizer management should be strengthened to improve the plant's disease resistance. Yellowing disease is a physiological disease, mainly caused by overly alkaline soil; for this disease, ferrous sulfate (0.2% solution) can be applied to adjust the pH, and more farmyard manure should be applied. Leaf sunscald disease has many causes, mainly poor site conditions (such as a large hardened area and a small green area, etc.), long periods of high temperature and drought, soil alkalinization or excessive flowering, etc.; comprehensive control measures such as increasing the frequency of watering, applying more fertilizer, and whitewashing the trunk can be adopted. Magnolia occasionally suffers from pests such as great bagworm moths and hawk moths in North China; if they occur, 20% diflubenzuron 8000-fold solution or 50% phoxim 1000-fold solution can be sprayed for control.

Because the branches and trunk of magnolia have relatively poor wound-healing ability, pruning is generally not done unless necessary. If the tree shape is unattractive or relatively messy, according to the actual situation the diseased and pest-infested branches, dry and dead branches, drooping branches, water sprouts, overly dense branches and useless branches can be thinned out, so as to facilitate ventilation and light transmission and produce a beautiful tree shape. The pruning time is before leaf expansion in early spring. Magnolia is generally not headed back, so as to avoid cutting off flower buds.