Hydrangea Fertilizer - Knowledgebase Question

Studio City, Ca
Question by robinhaffner1
April 30, 2008
I have been told that I should fertilize my hydrangeas with an acid fertilizer to make the blossoms blue. Last year they blossomed pink. What should I use?

Answer from NGA
April 30, 2008


Hydrangea blooms 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. Since your soil is probably alkaline, add aluminum sulfate to the soil in February or March and this summer's blooms should be blue.

For future reference, Miracle-Gro is a slightly acidified fertilizer.

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