Potted Magnolia Yellowing and Brown Spots: Water, Fertilizer, and Algae

Diagnosing Container Magnolia Issues

A 9-ft potted magnolia with daily watering, yellowing leaves, brown spots (non-crispy), and new growth browning—last fertilized 3 weeks ago with acidic azalea food—has three interacting issues:

1. Overwatering: Daily = waterlogged roots; magnolias need drainage.
2. Excess acid fertilizer: Magnolias like acid but not azalea-level low pH.
3. Parasitic algae (Cephaleuros): Brown spots on lower leaves—common in humid, overwatered containers.

Corrective Plan

• Water only when top 2" dry—not daily.
• Stop acidic fertilizer—use balanced slow-release.
• Treat algae: Hi-Yield Copper Fungicide spray; repeat in 7–10 days.
• Verify pot drainage—add holes if needed.

Normal Leaf Drop

Magnolias are semi-evergreen—shed leaves twice yearly. Some yellowing is natural; spots + new growth browning = cultural issues.