Grandfather's Baking Soda Spray for Tomatoes: Does It Work?

Old Italian recipe: 1 quart warm water + 1 tbsp baking soda + 1 tsp dish soap + 1 tbsp vegetable oil. Good for mildew and aphids—maybe not much else.

Effectiveness

• Powdery mildew: Baking soda alters leaf pH, inhibiting fungal spores
• Aphids: Soap + oil smothers soft bodies
• Other insects: Limited evidence

Critical Adjustment

Use 1 gallon water, not 1 quart. Concentrated mix risks leaf burn. Test on one leaf, wait 24 hours before full application.

Better Organic Alternatives

• Potassium bicarbonate (commercial, more effective than baking soda)
• Neem oil (broad spectrum, fungicide + insecticide)
• Copper fungicide (Soap Shield) for serious disease
• Insecticidal soap (targeted, safe)

Application Rules

• Early morning or evening only
• Thorough coverage, especially undersides
• Weekly for prevention; every 3–5 days for active issues
• Stop 2 weeks before harvest

Grandpa's brew works for mild mildew/aphids. For serious problems, upgrade to targeted organics.