What to Do When Hydrangea Leaves Turn Black
Hydrangeas are beloved by gardening enthusiasts for their full, fluffy flower heads, but sudden blackening and burning of the leaves often leave caretakers at a loss. This phenomenon is usually caused by environmental imbalances and requires a systematic diagnosis from aspects such as light, water, and fertilization. This article will analyze the causes through four key dimensions and provide specific solutions.
1. Light Regulation Solutions
1.1 Analysis of Damage from Excessive Light
Hydrangeas are semi-shady plants, and continuous exposure to strong light for over 6 hours can cause chlorophyll to decompose, initially leading to yellowing at the leaf edges, which can develop into black scorch marks within 48 hours if untreated. New leaves are more susceptible to damage than old leaves.
1.2 Guidelines for Scientific Sunshade Operations
It is recommended to use a shade net with a 40% light blocking rate, and provide protection between 10:00-15:00. Damaged plants should be moved to a scattered light environment and treated with a mist of chilled mineral water (temperature 18-22°C) on the leaf surface to accelerate recovery.
2. Water Management Strategies
2.1 Criteria for Diagnosing Waterlogging
When the soil surface remains moist below 3 cm for more than 36 hours, it can cause root hypoxia. Typical symptoms include irregular black spots on the leaves from the bottom up, along with softened leaf stems.
2.2 Emergency Drainage Techniques
Insert 5-7 ventilation holes in the potting soil with bamboo sticks and tilt the pot 45 degrees to promote drainage. In severe cases of waterlogging, change the growing medium, mixing in 30% perlite to improve aeration.
3. Fertilization Remediation Plan
3.1 Identification of Fertilizer Burn Symptoms
Excessive nitrogen fertilizer can cause radial black spots between the veins, while excessive complex fertilizer results in leaf edge scorching. Unripe organic fertilizer can cause the entire leaf to carbonize.
3.2 Root Washing Operation Specifications
Submerge the plant with the soil ball in 25°C water, changing the water every 20 minutes for 2 hours. After washing the roots, apply EM bacteria solution (diluted 1000 times) to repair the roots.
4. Comprehensive Disease Control
4.1 Identification of Common Diseases
Leaf spot disease presents as circular black spots with a yellow halo, while rust disease appears as orange-brown powdery substance. The (T-J) disease forms concentric ring-like lesions.
4.2 Guidelines for Pesticide Selection
Fungal diseases are recommended to be treated with benomyl (diluted 1500 times) alternated with mancozeb (800 times), while bacterial diseases require treatment with kasugamycin (1000 times).
By systematically regulating light intensity, improving watering methods, precise fertilization, and timely disease prevention and control, the black leaf issue in hydrangeas can be fundamentally resolved. It is recommended to check the back of the leaves monthly, maintain good ventilation, and control diseases at the initial stage. Remember, preventive maintenance is more important than post-event remedies.