What causes yellowing leaves and leaf drop in white magnolia (Michelia alba)?
(1) Long-term nutrient deficiency. If nitrogen fertilizer has not been applied for a long time, or the pot has not been repotted or the water changed, the water lacks nitrogen and other nutrients, causing weak branches and leaves, and thin, yellow leaves. You need to promptly change to fresh culture water and gradually increase applications of dilute, fully decomposed liquid fertilizer or compound flower fertilizer.
(2) Excessive fertilization. Too much fertilizer causes new leaves to be thick and fleshy, often uneven and bumpy, while old leaves dry at the tips, turn scorched yellow and drop. Stop fertilizing immediately, increase the amount of water changed so the fertilizer is washed away, or immediately take the plant out of the pot, rinse the bulb with water, and replant it in the pot.
(3) Hot, high temperatures. If the plant is placed in a hot spot under direct strong sunlight, the tips and edges of young leaves are very likely to scorch, or the leaves turn yellow and drop. Move it promptly to a well-ventilated, shady spot.
(4) Excessive shade. If the plant is kept in a shady spot or a place with insufficient light for a long time, the branches and leaves will turn yellow.
(5) Alkaline water and soil. Because the water lacks soluble iron and other elements the plant can absorb, the leaves gradually turn yellow. When planting, choose acidic water and soil, and during the growing period often water with alum fertilizer water.
(6) Too dense and poorly ventilated. If too much nitrogen fertilizer is applied, the branches and leaves grow too lushly, and with no pruning for a long time, the inner branches and leaves get insufficient light, which easily causes leaves to turn yellow and drop. Fertilize reasonably and prune more to improve ventilation and light penetration.
(7) Dry air. When indoor air is too dry, plants often show dried leaf tips or scorched leaf edges. Take measures such as spraying water and covering with a plastic film cover to increase air humidity,
(8) Improper temperature. If the indoor temperature is too low in winter, the plant suffers cold damage, causing leaves to turn yellow and, in severe cases, to wither and die. If the indoor temperature is too high, the plant transpires excessively, and the roots cannot supply enough water and nutrients, which also makes leaves turn yellow. Please remember to adjust the indoor temperature promptly.
(9) Damage from pests and diseases. Leaf spot disease caused by infection with fungi and other pathogens easily causes local necrosis of leaves, with yellow spots or patches, and in severe cases the whole leaf withers, turns yellow and drops. After infection by mosaic virus, yellow-green mottled patches appear on the leaves; damage from scale insects, red spider mites and the like.
(10) Strong irritation. When preventing and controlling pests and diseases, using pesticide at too high a concentration, or contamination by toxic gases in the air, or suddenly watering with cold water when the temperature is high, can all easily cause the leaf tips or parts of the leaf surface to turn yellow and scorch, or even the whole plant to wither and die. Therefore, use pesticides reasonably and try to eliminate sources of air pollution. In midsummer, avoid watering flowers with cold water around midday. Finally, it should also be mentioned that yellow leaves on potted flowers are sometimes caused by one reason, but are often the result of multiple factors, so a correct diagnosis should be made before treating the root cause.