Brown leaves on a hydrangea signal that the plant is undergoing environmental stress or damage. This discoloration is a symptom, not a disease, indicating an underlying problem with the plant’s care or location. Before removing any leaves, accurately identify the source of the browning to ensure the correct long-term action is taken. Addressing the root cause is the only way to prevent the issue from recurring and promote healthy growth.
Diagnosing the Source of Brown Hydrangea Leaves
The appearance of the browning often provides the first clue about the source of stress, typically pointing to an imbalance in water management. Under-watering, especially during hot, dry periods, results in leaf scorch, where the leaf margins or tips turn dry and crispy brown. This occurs because the roots cannot supply water quickly enough to meet the demand of the leaves, causing the outermost tissue to dehydrate.
Conversely, overwatering or poor drainage can lead to root rot, which manifests as dark, mushy, or blackened patches on the leaves. When roots are constantly saturated, they are deprived of oxygen and begin to die. This limits the plant’s ability to absorb water and nutrients, paradoxically mimicking the symptoms of drought stress. The distinction between crispy edges and dark, wilted patches is a useful initial diagnostic tool.
Environmental exposure is another common factor, particularly sun scorch, which affects leaves exposed to intense afternoon light. Hydrangeas planted without adequate protection often develop large, bleached or brown patches on the sun-facing side of the shrub. This damage results directly from high heat and excessive light exposure overwhelming the leaf tissue.
Fungal diseases also cause distinct browning patterns. Cercospora leaf spot appears as small, circular blackish-purple spots that may develop tan or gray centers, usually beginning on the lower, older leaves. Anthracnose, another fungal infection, creates larger brown spots with lighter centers, sometimes appearing on the flowers.
Nutrient imbalances can also cause discoloration. Fertilizer burn appears as brown, scorched margins due to an excess of soluble salts near the roots. If the soil pH is too alkaline, the plant may struggle to absorb iron, causing new leaves to turn yellow while the veins remain green. This condition, called iron chlorosis, can progress to browning if left uncorrected.
The Pruning Decision: When and How to Remove Damaged Foliage
The decision to cut off brown hydrangea leaves should be based on the degree of damage and the underlying cause. If only a small portion of a leaf is brown, it may still contribute to photosynthesis and is often best left alone. However, removing leaves that are more than 50 percent damaged improves the plant’s appearance and is generally recommended.
When removing foliage, the goal is to eliminate dead or diseased tissue without causing stress to the healthy parts of the plant. Use sharp pruning shears or scissors sterilized with rubbing alcohol or a 10 percent bleach solution. This sterilization step prevents the accidental transmission of fungal or bacterial spores to healthy tissue.
For individual leaves, cut the leaf stem (petiole) as close as possible to the main branch without damaging the bud at the base. If the entire branch is heavily damaged or dead, trace it back to the next healthy set of leaves or the main stem and remove it completely. Pruning dead tissue tidies the plant and can reduce the spread of fungal pathogens, but it does not fix the original problem.
Corrective Action and Long-Term Prevention
Correcting the source of the browning requires specific adjustments to the plant’s environment and care routine. Addressing water stress involves shifting from frequent, shallow watering to deep, infrequent soaking, aiming for approximately one inch of water per week. This encourages deep root growth and should be applied directly to the soil to avoid wetting the foliage, which encourages fungal development.
For hydrangeas suffering from sun scorch, the solution is providing shade during the intense afternoon hours (11 a.m. to 4 p.m.). This may involve relocating a container plant or installing a temporary shade cloth for shrubs planted in the ground. Applying a two to three-inch layer of organic mulch around the base helps moderate soil temperature and retain moisture.
If nutrient or salt buildup is suspected, the soil should be flushed thoroughly by applying a large volume of water to leach excess salts away. For plants struggling with iron deficiency due to alkaline soil, incorporating acidic amendments like elemental sulfur or compost can help lower the pH over time. Aluminum sulfate can also be applied, but it must be used sparingly to avoid root damage.
When a fungal infection like Cercospora is confirmed, sanitation is the first step, including clearing all infected leaf debris from the ground. Improving air circulation by selectively thinning crowded stems reduces the humidity that fungi thrive in. If the disease is severe, a fungicide containing chlorothalonil or thiophanate-methyl may be applied, following the product’s instructions.