Changing Hydrangea Color - Knowledgebase Question

Tracy, CA
Question by kevin_jordan
April 24, 2000
How do I get Hydrangeas to bloom in the beautiful pink, blue, purple or creamy green color? What do I need to know about the soil for this type of plant. How do you change acid quality in the soil for a specific color bloom and can you change the original blooms color by the acid level of the dirt?


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Answer from NGA
April 24, 2000

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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.

With the exception of Oakleaf hydrangea, which can be pruned to the ground each autumn, hydrangeas produce flowering shoots in the spring on last season's wood. So, to prune for flowering, reduce the old wood by one-half to one-third after bloom. The shrub will develop new flowering wood the following spring.

Hope this answers all your questions!

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