What Causes Hydrangea Leaves to Turn Yellow
The yellowing of hydrangea leaves is one of the most common abnormal phenomena in horticultural maintenance. This color change not only affects the ornamental value but may also indicate health issues in the plant. By systematically analyzing the causes of yellow leaves and taking targeted measures, you can quickly restore the vitality of your hydrangea.
I. Imbalance in Water Management Leading to Yellow Leaves
1.1 The dialectical relationship between water deficiency and waterlogging
Hydrangeas have fleshy roots that are intolerant to drought and afraid of waterlogging. Not watering for 5 consecutive days can cause the capillary roots to dehydrate and die, resulting in the edges of old leaves becoming scorched. Accumulated water for more than 24 hours can cause root rot, with new leaves turning yellow first. It is recommended to use the finger test: insert the index finger into the second knuckle of the soil, and water immediately if it is dry.
1.2 Four-step Scientific Watering Method
① Keep a watering cycle of 3-5 days in spring and autumn; ② Water twice a day in summer, early morning and evening, avoiding noon; ③ Water once every half month in winter; ④ Using the immersion pot method ensures even penetration. After discovering rotten roots, immediately trim the black roots, soak them in carbendazim for 30 minutes, and then plant in new soil.
II. Nutritional Imbalance Leading to Yellowing
2.1 Guide to Identifying Deficiency Symptoms
When nitrogen is deficient, old leaves turn yellow evenly; insufficient iron causes new leaves to lose green between the veins; and magnesium deficiency shows net-like yellow spots. It is recommended to apply a special acidic fertilizer (N-P-K=15-5-10) monthly, and spray chelated iron foliar fertilizer every two weeks.
2.2 Solution for Fertilizer Burn Repair
When fertilizer burn occurs, immediately follow a three-step process: rinse the potting soil 3-5 times → cut off 1/3 of the branches and leaves to reduce transpiration → move to a shady place for maintenance. In severe cases, replace 60% of the new soil, mixing in pearl rock to improve aeration.
III. Dynamic Control of Light Intensity
3.1 Golden Light Intensity Formula
The suitable light intensity for hydrangeas is 15000-25000Lux. They can accept full sunlight in spring and autumn, need 60%-70% shading in summer, and should ensure 4 hours of direct sunlight in winter. When using shading nets, keep a 50cm ventilation distance to avoid forming a hot and stuffy environment.
3.2 Emergency Treatment for Excessive Light Intensity
When sunburn spots are found, immediately move the plant to the shade and spray with a 0.1% brassinolide solution for repair. Spraying water in the morning and evening for 3 days can effectively restore leaf vitality.
IV. Systematic Optimization of Soil Environment
4.1 Substrate Improvement Formula
The ideal cultivation substrate ratio is: peat soil: pine needle soil: perlite = 5:3:2. Apply sulfuric acid iron (1:1000) every quarter to adjust the pH to 5.5-6.0. To improve compacted soil, add 20% decomposed pine bark to enhance granular structure.
4.2 Root Activation Technology
Combine potting with root pruning, retain 15cm of main roots, soak in indole butyric acid rooting solution, and then plant. After potting, keep the bag moist for 7 days, gradually increase the ventilation time, which can increase the new root mass by 200%.
By establishing a four-in-one maintenance system of water, nutrition, light, and soil, combined with regular observation and recording, the yellowing of hydrangea leaves can be effectively prevented. It is recommended to conduct leaf microscopic examination monthly and use an EC value tester to monitor soil conditions for precise maintenance. Remember, healthy hydrangea leaves should show a glossy deep green color; any color change is a distress signal from the plant.