Azalea Chlorosis in California: Iron, pH, and Drainage

Azaleas in Central Valley CA (sandy loam) show severe chlorosis (yellow leaves, green veins). Iron supplements failed. Rhododendrons nearby are healthy.

Diagnostic Steps

1. Soil test: Check pH (azaleas need 4.5–6.0), iron, manganese, zinc.
2. Check drainage: Even sandy soil can have perched water tables. Probe 12 in. deep; if wet/dark, improve drainage.
3. Root health: Inspect for root rot (Phytophthora) – brown, mushy roots.
4. Compare sites: Are chlorotic plants lower, wetter, or more shaded?

Remedies

• Soil acidification: Elemental sulfur (slow) or ammonium sulfate (faster).
• Chelated iron (EDDHA) applied as soil drench or foliar spray—works at higher pH.
• Mulch with pine bark to maintain acidity.
• Foliar feed with iron+manganese+zinc for quick green-up.

Why Rhododendrons Are Fine

Rhododendrons may be more tolerant of slightly higher pH or have better root systems. Test both areas.

Contact UC Cooperative Extension for local soil lab and specific recommendations.