Iron Chlorosis - Hydrangea
Rosie Lerner, Extension Consumer Horticulture
Specialist, Department of Horticulture & Landscape Architecture,
The interveinal chlorosis on this bigleaf
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.