Powdery Mildew on Rosemary: Diagnosis and Baking Soda Treatment

White, waxy powder on rosemary leaves = powdery mildew. Common indoors due to poor air circulation, low light, or irregular watering. Moving the plant outdoors in morning sun is the single best step.

Immediate Treatment

Baking soda spray:

• 1 tsp baking soda + 1 quart water (or 3 tbsp/gallon)
• Spray tops and undersides of leaves every 3 days for 9 days
• Rinse leaves before culinary use
• Non-toxic, safe for edibles

Prevention & Recovery

• Full morning sun (east-facing ideal)
• Excellent drainage – terra cotta pot, gritty soil
• Water at base only – keep foliage dry
• Space plants for airflow
• Prune affected growth after treatment

Rosemary prefers to stay outdoors year-round in zones 7+. Hardy cultivars 'Arp' and 'Hill Hardy' survive colder winters with protection.