What to do if海棠 leaves turn yellow, prevention and control techniques for海棠 yellow leaf disease.

How to deal with the yellowing of crabapple leavesAs a deeply loved ornamental plant, the yellowing of crabapple leaves often puzzles maintainers. Yellow leaves not only affect the ornamental value but also serve as a health alert from the plant. This article systematically analyzes six core maintenance points from water management to environmental control, helping you accurately locate the root cause of the problem.Key points of maintenance managementScientific water control to prevent waterlogging damageSynchronous yellowing of young and old leaves is a typical symptom of waterlogging. It is recommended to use the "fingertip test": water when the second knuckle of the index finger inserted into the soil is dry, with terra cotta pots needing shorter cycles due to faster evaporation. During the rainy season, tilt the pot 45 degrees to accelerate drainage, and place broken tiles at the bottom of the pot to improve breathability.Accurate fertilization to supplement nutritionNutrient deficiency yellowing starts from the veins of the leaves. Apply iron chelate fertilizer every half month during the growing season, supplemented with mature soybean cake water to replenish trace elements. Follow the principle of thin and frequent fertilization, and reapply if it rains within 24 hours after fertilization. Fertilization should be stopped during the winter dormancy period.Skills of environmental regulationLight intensity classification managementReceive full sunlight in spring and autumn, filter 40% strong light with a sunshade net in summer, and ensure at least 4 hours of direct sunlight in winter. For indoor maintenance, use a 2000-3000lux grow light, 30cm away from the leaf surface, with 6 hours of supplemental lighting daily.Air circulation system constructionClosed environments can easily trigger red spider mites, so it's necessary to maintain an air velocity of 0.3-0.5m/s. For balcony maintenance, install a mini circulation fan and ventilate three times a day, each for 20 minutes. Avoid direct through drafts, as excessive wind speed can accelerate leaf transpiration.Soil system optimizationDynamic pH adjustmentTest the soil with pH paper every month and maintain it within the optimal range of 5.5-6.5. Use sulfur powder (0.5g per liter of soil) to adjust alkaline soil, combined with a 1000x solution of ferrous sulfate for root irrigation. Recommended matrix formula: peat soil: pine needles: perlite = 5:3:2.Root health monitoringCheck the roots every spring when potting, trim blackened and rotting roots, and soak in a 800x solution of carbendazim. The new pot diameter should be 3-5cm larger than the original pot, with the pot preference being breathable purple sand or unglazed ceramic pots.By following the above systematic maintenance plan, combined with regular leaf wiping (wiping the leaf surface with beer diluted solution monthly) and night-time temperature control (maintaining a 15-18℃ temperature difference), new leaves usually turn green within 2-3 weeks. It is recommended to create a maintenance log, recording data such as watering time and fertilization amounts, to gradually establish a personalized maintenance model.