Petunia Foliage Browning from Base Up? Likely Powdery Mildew

Petunias in cement pots grow huge and gorgeous, but every year foliage browns from the bottom up. Air circulation improvements (staking) don't help. The gardener avoids chemicals.

Diagnosis

Most likely powdery mildew—check living leaves near dead ones for a faint grayish powdery coating. Other possibilities: water stress (drying between waterings) or fertilizer burn (feeding dry plants).

Organic Management

• Preventative sprays: GreenCure or Serenade (both organic, Bacillus-based) applied early and regularly next season.
• Current season: Cut back affected stems to stimulate new growth. Spray with above products now.
• Soil hygiene: Replace all potting soil annually—mildew spores overwinter in old soil.
• Watering: Water deeply, less often. Avoid wetting foliage.

Powdery mildew is common on dense, mature petunias. Consistent organic prevention beats reactive treatment.