how to color blue or pink - Knowledgebase Question

phoenix, Ar
Question by lloydwilz
April 3, 2010
I grow hydrangea plants and want to know how to make the various colors.


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Answer from NGA
April 3, 2010

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Soil pH is the key to hydrangea color. Soil acidity or alkalinity will change the color of hydrangea blooms. Pink and red hydrangeas often turn blue or purple in acid soils. For blue flowers, treat the soil with 2 Tablespoons of aluminum sulphate per plant, making 4-6 applications at 2 week intervals, starting in the early spring before the plants bloom. (Sulfur will acidify the soil. The desired pH range would be between 5.5 and 6.) Plants can be made pink or red by applying superphosphate or liming the soil to raise the pH above 7.8. Test your soil to measure the pH range. In general, 4 ounces of lime around the base of your hydrangea plant can change the pH of your soil by one point. Ditto with superphosphate or lime.

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