Answer: Pink and red hydrangeas often turn blue in acid soils. You can keep hydrangeas blue by applying aluminum sulfate to the soil. You can keep red hydrangeas red by liming the soil or applying superphosphate. Soils in the Pacific Northwest are generally acidic, so most hydrangea flowers will become blue. If you want to preserve pink or red colors in your plants, use superphosphate. Lime juice and coffee grounds are acidic in nature and will only further acidify your already acidic soil. To affect the colors of bloom, treatment should be started in February or March. Hope this information helps!
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