Magnolia Chlorosis: Yellowing Leaves Need Iron, Not Just Nitrogen

Sudden July Leaf Drop on Mature Magnolia: Chlorosis Diagnosis

Your 20+ year magnolia is dropping leaves in July, turning yellowish with some mildew. No herbicide used? It’s likely iron chlorosis from alkaline soil. Magnolias need neutral to slightly acidic, well-drained, rich soil.

Iron Treatment Options

• Iron chelates (preferred): Soil-applied per label; some can be foliar-sprayed but soil is longer-lasting.
• Ferrous sulfate: Foliar: 2.5 oz in 3 gal water (repeat often). Soil: 1 lb/gal water; apply 1 gal per foot of dripline diameter (dormant) or 0.5 gal/ft (growing season). Drill holes 3 ft apart around dripline for best results.

Also fertilize to stimulate growth (see OSU guide). Avoid herbicides near the tree.