The Q&A Archives: Color of flowers on a hydrangea bush

Question: What determines the color of the flowers on a hydrangea bush? I bought a bush with blue flowers but it now produces pink flower. Is it due to the acidity of the soil?

Answer: Hydrangea bloom color can be affected by soil pH. A somewhat acidic 5.5 should turn them blue, a more alkaline 6.0 should turn them pink with the effect being more intense the more extreme the pH. Pink and red hydrangeas often turn blue or purple in acid soils. Blue hydrangeas can turn pink in alkaline soils. Plants can be made (or kept) blue by applying aluminum sulfate to the soil; plants can be kept pink by liming the soil or applying superphosphate. If your soil is alkaline, add aluminum sulfate to the soil in February or March and next summer's blooms should be blue. Best wishes with your hydrangea.

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