Overdosing Hydrangea with Aluminum Sulfate: Recovery Options

Applying aluminum sulfate repeatedly to turn pink hydrangeas blue backfired—the leaves shriveled and browned. Aluminum becomes toxic to plants at high concentrations, especially in acidic soil. The sulfur in aluminum sulfate lowers pH, increasing aluminum availability; one application might be safe, but multiple doses created toxicity.

Two options: (1) Dig up the plant, replace the contaminated soil, and start fresh with a new hydrangea. (2) Apply hydrated lime (1 cup per gallon, one time only) to raise pH and counteract acidity, then wait and see next spring. Unless the plant has sentimental value, replacement is the surer path.