Key Points for Sowing Flowers in the Four Seasons and the Causes of Yellowing Leaves in Potted Plants
Because potted flowers are restricted in their development, if they are not well managed and cared for properly, they are more prone to leaf yellowing than flowers grown in open ground. In mild cases, their appearance is diminished; in severe cases, the entire plant dies. The causes, symptoms and remedial measures are described below:
1. Water yellowing: Overwatering causes water to accumulate in the pot soil and remain wet for a long time, resulting in a lack of oxygen in the soil, which causes some fibrous roots to rot, thereby weakening the ability to absorb water and nutrients. This causes young leaves to turn pale yellow, and variegated leaves also gradually turn dark yellow. Once discovered, watering should be controlled immediately, fertilizing stopped, and the soil loosened frequently to keep the pot soil well aerated. In severe cases, the entire root ball needs to be removed from the pot and placed in a pile of dry soil so that moisture seeps out quickly; after the drooping branches and leaves recover, replant it in the pot.
2. Drought yellowing: Watering too little, or watering only halfway or missing watering for a long time, causes the leaves to evaporate more water than they absorb, creating a water shortage, which also causes leaves to turn yellow. "Drought yellowing" starts from the lower leaves and gradually moves upward, turning yellow, scorched and falling off; in severe cases, the petioles droop and appear wilted. Once discovered, the pot must be moved to a cool place immediately, some water sprayed on the leaves, and a small amount of water poured. Later, as the stems and leaves gradually regain their upright posture, the amount of watering should be increased gradually. If too much water is suddenly poured at this point, it may cause plasmolysis, damage the protoplasm, and cause the flower to die.
3. Fertilizer yellowing: Applying too much fertilizer, especially too much nitrogen fertilizer while lacking phosphorus and potassium fertilizer, easily causes leaves to turn yellow. It appears as new leaves that are thick and fleshy, with mostly uneven leaf surfaces, while old leaves gradually turn yellow and fall off; in severe cases, the leaf tips dry up, and even the entire leaf becomes scorched yellow. In this situation, fertilizing should be stopped immediately, watering increased so that fertilizer flows out through the drainage holes, or the pot should be repotted immediately, part of the old soil removed, the root ball washed with water, replaced with some new potting soil, and the plant replanted in the pot.
4. Starvation yellowing: Insufficient fertilizing, especially when nitrogen fertilizer has not been applied or the potting soil has not been changed for a long time, leads to a lack of nitrogen nutrition in the soil, causing weak branches and leaves, and thin, yellow leaves. The pot should be changed in time, the plant removed, replanted in a pot one size larger with fresh, loose, fertile potting soil, and replanted properly. After watering thoroughly, place it in a semi-bright place to recover. After it resumes growth, apply dilute liquid fertilizer or compound fertilizer.
5. Alkaline yellowing: When acid-loving flowers are grown in the north, such as camellia, orchid, banana shrub, gardenia and osmanthus, because the soil in most northern regions contains more salt and alkali, after being cultivated for a period of time, the above plants gradually lose green and turn yellow due to a lack of soluble iron that the flowers can absorb. At this time, 0.2% ferrous sulfate solution can be applied at intervals, and at the same time 0.1% potassium dihydrogen phosphate solution can be applied alternately, so that "alkaline yellowing" is cured. At the same time, potassium dihydrogen phosphate also contains phosphorus and potassium, which is beneficial to flower bud differentiation and improving flower quality.
6. Acid yellowing: In southern China, the soil is red earth, and the soil is acidic or slightly acidic. Magnesium in the soil is easily lost, and due to magnesium deficiency, leaves often show yellowing first between the veins of old leaves. Calcium magnesium phosphate fertilizer can be applied. Plants such as lucky bamboo are harmed, causing leaves to turn yellow and fall off; if the room temperature is below 5°C, most flowers that like warmth and fear cold will also be harmed, with leaves, flowers and fruits turning yellow, drying up, and falling off easily. Therefore, after bringing them indoors, a 0.1% to 0.3% magnesium sulfate solution should be sprayed according to the situation. For improving acidic soil, attention should be paid to applying more decomposed organic fertilizer and applying lime. Applying a small amount of lime can not only neutralize soil acidity, but also promote the decomposition of organic fertilizer.
7. Sunburn yellowing: In summer, placing flowers that like semi-shade and fear high heat, such as asparagus fern, spider plant, clivia, cyclamen and fuchsia, in direct strong light for care can very easily cause young leaf buds or leaf edges to scorch, or the entire leaf to turn yellow. Once discovered, they must immediately be moved to a cool, well-ventilated place for cultivation.
8. Shade yellowing: If light-loving flowers are kept for a long time indoors in a place with insufficient light, their growth weakens, the leaves become thin and yellow, and they do not bloom or bloom very little. When cultivating such flowers, they usually need to be placed outdoors in a sunny or semi-light place, and moved indoors for viewing only after blooming.
9. Dry yellowing: In northern winters, because heating or coal fires are used, the indoor air becomes dry. Some flowers that like humid air, such as orchids and Monstera deliciosa, under such environmental conditions are prone to dry leaf tips or scorched leaf edges, scorched spots on the leaves, and curled edges. Warm water close to room temperature should often be used to spray and wash the branches and leaves, and a basin of clean water should be placed on the radiator or stove to help increase indoor air humidity. For some precious flowers, it is best to cover them with a plastic film cover at night, and place a basin of clean water inside the cover. Local scorching of the leaves, or even death of the whole plant, may occur. Therefore, pesticides should be applied reasonably, efforts should be made to eliminate air pollution and avoid soil toxicity.
In addition, for growth that is too dense, spraying pesticide is likely to cause pesticide damage and cause leaves to wither and yellow; contamination by toxic gases in the air or poisoning by toxic substances in the soil can also cause this.
Finally, it should be pointed out that the mechanism of yellowing leaves in potted flowers is relatively complex. Sometimes it is caused by one reason, and sometimes by several reasons. Therefore, when yellowing leaves are found, careful observation and appropriate treatment are needed to achieve good results. At the same time, it should also be noted that not all yellow leaf phenomena are pathological diseases. For example, when the "autumn wind sweeps away fallen leaves," deciduous flower trees wither and shed leaves; annual herbaceous flowers wither and die; the aboveground branches and leaves of perennial flowers wither; when flowers are transplanted, due to temporary nutritional imbalance, a small amount of yellow leaves fall off; for individual flowers, such as flourishing branches and leaves that are not pruned for a long time, causing insufficient light in the inner branches, leaves are also prone to turning yellow and falling off. Attention should be paid to timely pruning so as to provide ventilation and light, and at the same time attention should be paid to appropriately applying more phosphorus and potassium fertilizer to prevent branches from growing excessively. Place a basin of clean water inside.
10. Cold yellowing: Northern winters are cold. If the room temperature is below 8°C at this time, some flowers that like high temperatures, such as poinsettia, croton, bougainvillea, peacock arrowroot, and various variegated flowers, have temperature requirements. Adjust the indoor temperature.
11. Pest and disease yellowing: When flowers are infected by pathogenic organisms such as fungi and viruses, various leaf spot diseases are caused, causing local tissue necrosis in the leaves, appearing as chlorotic yellow spots or yellow-green mottled patches, or the entire leaf turns yellow and falls off. When harmed by pests such as red spiders and scale insects, chlorophyll is destroyed, which can also cause yellow-white small spots on the leaves, or the leaf color to turn yellow and fall off. Once discovered, pesticide should be sprayed in time for control.
12. Toxin yellowing: When using pesticides to prevent and control flower pests and diseases, the concentration is too high, or in midsummer when the old leaves of hibiscus, white champaca and others turn yellow after new branches sprout, these are all normal physiological phenomena, not pathological diseases.