P&PDL Picture of the Week for
May 10, 2010

Iron Chlorosis - Hydrangea

Rosie Lerner, Extension Consumer Horticulture Specialist, Department of Horticulture & Landscape Architecture, Purdue University

The interveinal chlorosis on this bigleaf hydrangea (H. macrophylla) leaves is most likely a result of iron deficiency due to high pH. Note that the larger veins remain green with the space between the veins turning yellow. When severe, the chlorosis becomes nearly white with some necrosis on the leaf margins. Iron may be present in the soil, but becomes unavailable to for plant uptake in alkaline soil. The pink flower color also indicates an alkaline pH  (flowers are blue in acid soil).

The plant should respond quickly to a foliar spray of iron sulfate or iron chelate, but the response will be temporary and needs to be repeated every few weeks. A more long-term approach would be to lower the soil pH and/or apply chelated iron. Sulfur is most effective at lowering soil pH before planting, but can burn the roots if applied to existing plants. Use aluminum sulfate for established plants.

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Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service