There are many reasons why the yellow leaves of rhododendron are dry and sharp. Let's see which one is caused by you: (1) Too much watering, too much wetting of the basin soil for a long time, resulting in lack of oxygen in the soil, causing some fibrous roots to rot, hindering normal breathing and absorption of water and nutrients, and causing leaves to turn yellow and fall off. After injury, the young leaves first turn pale yellow, and then the old leaves gradually turn yellow. Water should be controlled immediately, fertilization should be suspended, and soil should be loosened frequently to make the soil well ventilated. (2) Drought dehydration. Leakage of flowers or long-term watering (that is, wet on the top and dry on the bottom) will affect nutrient absorption, and it is also easy to cause dull and drooping leaves. First, the lower old leaves are aging and gradually wither and fall off from bottom to top. At this time, it is necessary to water slightly, spray water to make it gradually recover, and then turn to normal watering. (3) Fertilize for a long time. Long-term non-application of ammonia fertilizer or changing pots and soil, the soil lacks nutrients such as nitrogen, which leads to sparse branches and leaves, thinning and yellowing. It is necessary to pour the pots in time, replace them with new loose and fertile culture soil, and gradually apply dilute and decomposed liquid fertilizer or compound flower fertilizer. (4) Overfertilization. If too much fertilizer is applied, new leaves will be thick and uneven, and old leaves will fall off in brown. Therefore, fertilization should be stopped immediately, and the amount of water should be increased to make the fertilizer flow out from the drainage hole at the bottom of the basin, or the basin should be emptied immediately, and the clods should be washed with water, and then replanted in the basin. (5) hot and high temperature. In summer, if the cool flowers (such as cyclamen, upside-down golden bell and begonia) are placed in a high temperature place and directly exposed to strong light, it is easy to cause the tips and edges of young leaves to burn or the leaves to fall off. It needs to be moved to a well-ventilated shade in time. (6) excessive shading. If the sunshine-loving flowers are placed in a cool place or a place with insufficient light for a long time, the branches and leaves will grow white, the leaves will become thin and yellow, and they will not bloom or rarely bloom. Be careful to move the flowerpot to a sunny place. (7) Soil and water are alkaline. The soil and water in most parts of the north contain more saline and alkali. When planting flowers that like acidic soil, such as azalea, camellia, smiling face, gardenia, orchid, magnolia, osmanthus, etc. Due to the lack of soluble iron and other elements that can be absorbed by the soil, the leaves will gradually turn yellow. Acidic soil should be used when planting, and alum fertilizer should be poured frequently during the growth period. (8) Dense ventilation. Excessive application of nitrogen fertilizer, lush growth of branches and leaves, long-term non-pruning, insufficient illumination of branches and leaves in the inner room, easy to cause leaves to yellow and fall off. Fertilization should be reasonable, and pruning should be strengthened to make it ventilated and transparent. (9) air drying. When the indoor air is too dry, some flowers that like humid environment, such as chlorophytum and orchid, often have the phenomenon of dry tip or scorched leaf edge. Attention should be paid to methods such as sprinkling water and covering with plastic film to increase air humidity, and (10) temperature is improper. When the room temperature is too low in winter, flowers that like high temperature are often vulnerable to cold damage, which leads to yellowing of leaves, and in severe cases, yellowing. If the room temperature is too high, the transpiration of plants will be too strong, the water and nutrients in roots will be in short supply, and the leaves will turn yellow. Please pay attention to adjust the room temperature in time. (1 1) The soil is slightly acidic. The red loam in the south is acidic, and magnesium is easy to lose. Flowers and trees planted with alkali-resistant or slightly sealed soil, such as oleander, boxwood, Yingchun, etc., are often easy to turn green and yellow between the veins of old leaves. Calcium magnesium phosphate or magnesium sulfate solution can be applied. (12) pests and diseases. Leaf spot caused by fungi and other pathogens is easy to make the leaves locally deteriorate and yellow spots or patches appear. In severe cases, the leaves are completely yellow and fall off, and yellow-green spots appear on the leaves after being infected with mosaic virus. Suffer from scale insects, red spiders, etc. The leaves will also become partially yellow and withered, or even the whole leaves will turn yellow and fall off. All should be sprayed in time to prevent and control. (13) Strong sexual stimulation. Too high concentration of pesticides used in pest control, or pollution of toxic gases in the atmosphere, or sudden pouring of cold water when the temperature is high, are easy to cause local yellowing, scorching and even withering of the whole plant. Therefore, we should pay attention to the rational use of pesticides and try to eliminate air pollution sources. Avoid watering flowers with cold water around noon in midsummer. Finally, the yellow leaves of potted flowers are sometimes caused by one reason, but often by many factors. Correct diagnosis can prescribe the right medicine.
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(14) alkaline defoliation, that is, yellowing defoliation, is mainly caused by long-term application of alkaline soil and water. It is characterized in that at the beginning, the new leaves change from green to light yellow, the old leaves are yellow but the veins are green, and then the leaves gradually fall off from bottom to top, leaving only the tip leaves in severe cases. Prevention and control measures: pay attention to the use of weak acid soil and water. After the disease occurs, firstly acidify the water to eliminate the alkalinity of the basin soil, add a little ferrous sulfate into the basin, and then replace the acidic soil after it returns to normal. "loose hair" soil, namely larch humus soil, has a PH value of about 4.5 ~ 5.0, which is an ideal high-quality cultivation soil for potted rhododendrons. (15) Fertile defoliation is "leaf burning" disease, also known as "leaf burning". It is characterized in that after topdressing (some topdressing takes a long time), the tips and edges of leaves are dried, showing dry tips or sharp edges. Then a lot of leaves fall, and in severe cases some branches lose water and dry up. The "leaf burning" disease seems to be a leaf disease, but it is actually a damage to the root system. If the one-time topdressing is too thick, the plant will appear "leaf burning" and branch shrinkage. Check the root cause of fat damage, and if it turns yellow, early treatment can restore it; If most of them are black, they are generally not easy to preserve. Specific treatment measures: once it is confirmed that fallen leaves are caused by fertilizer damage, dry manure should be removed immediately, and soil should be changed locally, but not all of them can be replaced and roots can not be washed. Water should be poured several times a day to dilute the fertilizer solution, then control the water and set up a shelter with strong astigmatism to keep the environment moist and slowly recover. Mainly feeding, it will take a year to recover. Rhododendron fertilization must highlight the word "light". (16) strong sunlight defoliation. Rhododendron likes half yin and fears strong yang. Rhododendron was exposed to strong light, which caused the leaves to wither, shed a lot of leaves and even die. It is characterized in that, at the beginning, the leaf edge turns from green to brownish red or brownish yellow, showing the phenomenon of "aging". Then, the dry edges and tips of the leaves shed a lot, which is very similar to the prevention and control measures of "fertilizer damage": after confirming that the leaves are defoliated by strong sun, the rhododendron in the courtyard should be moved to the shade of the courtyard or under the north corner immediately; The cuckoo in the building should be placed on the protective cover of the north balcony or the north house. In this way, the sunshine time can be controlled in the morning and evening, accounting for 1/3 or 1/2 of the total sunshine time, which is an ideal shade environment for raising rhododendrons. In this environment, the new leaves of diseased plants will grow rapidly and return to normal within a month or two. Rhododendron leaves are green and grow well in the semi-cloudy environment with sunshine in the morning and evening.
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(17), defoliation due to environmental discomfort. Rhododendron likes humid and cool climate, not suitable for high temperature and high dryness. Under family conditions, leaves are often abnormal or even "aging" because of insufficient humidity, or "flashing seedlings" because of frequent indoor and outdoor sports; Or put it in a heated room in winter and "burn" the leaves. All the above are fallen leaves caused by environmental discomfort, so we should pay attention to the following aspects in management: ① Proper moisturizing, and it is best to adopt the "moisturizing method"; (2) To prevent the temperature from changing drastically, especially in winter, don't move indoors when staying in one place, and don't move alternately between hot and cold rooms or rooms and balconies; ③ Prevent poor ventilation. Rhododendrons should be placed outdoors in summer, especially indoors with air conditioning. If it is placed indoors with heating in winter, it is necessary to properly open the window for ventilation, preferably at Nanyang Terrace; (4) Smoke prevention, not in the kitchen or living room where people smoke and the air is dirty; ⑤ Strictly grasp the timing of leaving and entering the room. The removal time of azaleas should be later in spring, and the indoor and outdoor temperatures should be basically balanced at night. The temperature at night should generally not be lower than 10℃. It is also appropriate to control the temperature around 10℃ at night when entering the room in autumn. (18) fallen leaves caused by red spider. Leaves turn yellow, which is easy to appear when they are dry at high temperature. 3 ~ 5 degrees sulfur mixed solution is used in dormancy period, 40% dimethoate or 50% naloxone 1000 times solution is sprayed in dormancy period, and 20% dicofol alum is sprayed in other periods. The above information is for reference only. Welcome to consult again!