06/02/2026
Most hydrangea problems show up on the leaves before anything else goes wrong. Knowing which symptom points to which cause is the difference between a targeted fix and repeated guessing. 🌿
Twelve symptoms to recognize:
Frost damage — dark brown or black patches on leaf edges and tips, typically appearing after a late frost or cold snap. Affected tissue is crisp and dry. Cut back damaged stems to healthy wood once new growth begins.
Sunscald — large bleached or tan dry patches on leaves exposed to intense afternoon sun. Most hydrangeas prefer morning sun and afternoon shade. Move containers or add shade cloth.
Chlorosis — yellow leaves with green veins remaining, often starting on newer growth. Usually indicates iron deficiency caused by high soil pH. Test the pH — most hydrangeas want 5.5 to 6.5. Acidify with elemental sulfur or iron chelate application.
Over-fertilization — brown crispy leaf margins and tips, especially after applying fertilizer. The salt concentration in the soil draws moisture out of the roots. Flush with deep watering and reduce nitrogen applications.
Scale insects (soft or armored) — small waxy or shell-like bumps on stems and the undersides of leaves. Heavy infestations cause yellowing and dieback. Treat with horticultural oil in dormancy or insecticidal soap on active crawlers.
Spider mites — fine stippling across the leaf surface, sometimes with webbing on the undersides. Worse in hot dry conditions. A strong blast of water clears light infestations; insecticidal soap or neem oil for heavier pressure.
Thrips — silvery streaking or flecking on leaves, sometimes with distorted new growth. Sticky traps help with monitoring; predatory insects and spinosad-based sprays are effective.
Downy mildew — yellow patches on the upper leaf surface with a grey-purple fuzzy growth on the underside. Caused by wet conditions and poor airflow. Remove affected foliage and improve spacing.
Cercospora leaf spot — circular tan or purple-bordered spots on the leaves, often with a purple halo. Common in humid climates. Improve airflow, apply copper-based fungicide if persistent.
Powdery mildew — white or grey chalky coating on the leaf surface. Worse in humid weather with poor circulation. Remove heavily affected leaves and apply baking soda spray or sulfur-based fungicide.
Anthracnose — irregular brown or tan blotches that enlarge in wet weather, often with a water-soaked appearance at first. Remove affected material and avoid overhead irrigation.
Botrytis — soft grey-brown rot on leaves, stems, and spent flowers, with a visible grey fuzzy mold in humid conditions. Remove affected tissue and increase airflow. 🌱
One practical note: root and stem rot, bacterial infection, and virus are also shown in the source image. Root rot shows as wilting despite moist soil — typically a drainage or overwatering problem. Bacterial infections produce angular water-soaked lesions. Virus causes mottled or mosaic patterning and has no cure — remove affected plants to prevent spread.
