What Causes the Yellowing of Orchid Leaves
The yellowing of orchid leaves is a common issue in the maintenance process, which not only affects the ornamental value but also indicates potential health risks of the plant. This article systematically analyzes the four main causes and provides practical solutions to help orchid enthusiasts accurately diagnose the problem.
I. Light Imbalance Leading to Yellow Leaves
Characteristics of Sunburn Damage
Except for a few varieties like Cymbidium, 90% of orchids are suitable for a diffused light environment. When the daily average light intensity exceeds 30,000 lux, the structure of chloroplasts is damaged, resulting in leaf tip scorching and yellow spots on the leaf surface.
Scientific shading plan
Immediately cut off the yellowed leaves, use a 60% shade rate aluminum foil shading net, and place it on a window sill that allows north-south ventilation. It is recommended to receive direct sunlight before 10 a.m. from late spring to mid-autumn.
II. Temperature Abnormalities Causing Lesions
Manifestation of Low Temperature Frost Damage
When the ambient temperature is below 10℃ for 48 consecutive hours, the permeability of cell membranes changes, and radial yellowing appears between the veins. Tropical varieties like Cattleya and Cymbidium are particularly sensitive.
Key Points of Constant Temperature Maintenance
Use a step-up heating method, increasing the temperature by 2-3℃ per day until the ideal range of 18-25℃ is reached. In winter, use a heating pad to maintain the pot bottom temperature, and create a microclimate with a double-layer insulating film.
III. Key Points of Water Management
Diagnosis of Dehydration Yellowing
When the top 2cm of the planting material is completely dry and the pseudobulb shows shrinkage, it indicates severe water deficiency. The leaves turn yellow uniformly from bottom to top, becoming brittle and easy to break.
Gradual Watering Strategy
Use the immersion pot method to water, with the water level not exceeding 2/3 of the pot height, soak for 20 minutes and then drain. Subsequently, maintain the humidity of the planting material at 40%-60%, and use an air humidifier to keep the ambient humidity at 60%.
IV. Complications from Nutritional Imbalance
Identification of Deficiency Symptoms
Lack of nitrogen causes the entire old leaf to turn yellow, while lack of iron causes the loss of green between the veins of new leaves. Over-fertilization can lead to salt accumulation, causing brown crispy edges on the leaf margins.
Scientific Fertilizing Plan
Apply orchid-specific slow-release fertilizer monthly during the growing season, with the EC value controlled at 0.8-1.2mS/cm. In case of fertilizer damage, immediately rinse the planting material with pure water for 3 consecutive times, and replace the new substrate in severe cases.
By adjusting light, managing temperature, balancing water, and providing nutrition, along with regular pest and disease inspections, the yellowing of orchid leaves can be effectively prevented. It is recommended to conduct leaf surface inspections every quarter and track maintenance data using a gardening logbook for precise management.