Hydrangea leaves turning yellow: causes and fixes

The most common causes of yellow hydrangea leaves are: iron chlorosis in alkaline soil, overwatering and root problems, natural lower-leaf senescence, and nitrogen deficiency. Iron chlorosis is distinctively interveinal — yellow tissue between green veins on new growth. Overwater

Yellow hydrangea leaves are a reliable source of gardener confusion because the same symptom pattern — yellowing interveinal tissue — can come from opposite soil conditions: too acidic (iron locked up), too alkaline (same effect), or simple nutrient rundown. Knowing where the yellowing appears on the plant and what pattern it follows is the path to a correct diagnosis.

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The most important first question: where is the yellowing?

Per Penn State Extension, "the location of yellowing on the plant is the best first diagnostic clue." Three patterns:

1. New growth (young upper leaves) is yellowing: Iron, manganese, or sulfur deficiency — usually a soil pH problem
2. Old growth (lower, older leaves) is yellowing: Nitrogen deficiency, normal senescence, or overwatering
3. All leaves yellowing at once: Root problem — either overwatering/root rot, or transplant shock