The sight of scorched, brown, and crispy leaves on a hydrangea can be alarming, making it appear burnt or dying. This visual damage, which can range from brown edges to entire necrotic patches, signals that the plant is under severe stress. This appearance is a symptom, indicating an imbalance in the plant’s environment or its care routine. Understanding the precise cause of this “burning” is the first step toward restoring the hydrangea’s health.
Diagnosis: Sunscald and Heat Stress
Hydrangeas, particularly Hydrangea macrophylla (Bigleaf Hydrangea), are understory plants that thrive with morning sun and afternoon shade. When these shrubs are exposed to intense, direct afternoon sunlight, especially during the summer, they can suffer from sunscald. This damage occurs when the sun’s energy causes the leaf tissue to overheat, resulting in large, irregular patches of bleached or brown, crispy tissue that often appear suddenly on the most exposed leaves.
High ambient temperatures significantly exacerbate this issue, causing heat stress even if the soil moisture is adequate. The plant attempts to cool itself through transpiration, a process where water moves from the roots through the leaves and evaporates. If the surrounding air is too hot or dry, the rate of water loss exceeds the rate of absorption, causing the plant’s cellular structure to collapse, leading to the scorched appearance. This type of damage is typically concentrated on the upper canopy and the side facing the intense afternoon sun.
Diagnosis: Chronic Dehydration and Water Stress
The most frequent cause of a burnt appearance is chronic water stress, often due to insufficient moisture in the root zone. Hydrangeas are known for their high water demand, and when the roots cannot supply enough water to the leaves, the plant sacrifices vulnerable tissues to conserve moisture. The initial symptom is often wilting during the hottest part of the day, which usually resolves itself overnight when temperatures drop.
If the dehydration is not addressed, the wilting progresses to permanent damage, characterized by brown, crispy edges that start at the tips and margins of the leaves. This marginal necrosis is a sign that the plant is unable to maintain turgor pressure in the peripheral cells. Poor soil structure, such as overly sandy or compacted clay, contributes to this problem by either failing to retain water or preventing deep water penetration, even if the gardener waters frequently.
Diagnosis: Fertilizer and Chemical Damage
A burnt appearance can also be the result of a chemical imbalance, most commonly caused by over-fertilization, known as salt burn. Fertilizer salts, which include compounds like nitrogen, phosphorus, and potassium, draw moisture out of the roots via osmosis if they accumulate in high concentrations. This effectively dehydrates the plant at a cellular level, even in moist soil, leading to a distinct, uniform brown band of necrosis around the leaf margins.
Applying fertilizer directly to dry soil or using excessive amounts intensifies the concentration of these soluble salts, which can physically damage the delicate root tips. Another chemical culprit is herbicide drift, where weed killers sprayed nearby are carried by the wind to the hydrangea. This damage typically appears as distorted, cupped, or curled new growth in addition to browning and necrosis, distinguishing it from simple salt or heat burn.
Actionable Steps for Recovery
The first step in recovery is to remove the damaged foliage, as scorched or necrotic leaves will not turn green again. Their removal allows the plant to focus energy on new growth. If dehydration is suspected, provide immediate deep watering by allowing water to soak slowly into the root zone for an extended period, which helps rehydrate the entire root ball. Use a soaker hose or drip irrigation to ensure the water penetrates deeply rather than running off the surface.
To prevent future sunscald, consider erecting a temporary shade cloth or moving container plants to a location that receives only morning sun. For plants damaged by fertilizer burn, thoroughly flush the soil with plain water multiple times over several days to leach out the excess soluble salts. This process dilutes the harmful concentration away from the roots. Finally, apply a two to three-inch layer of organic mulch around the plant, keeping it away from the main stem, to help keep the roots cool and conserve soil moisture.