|I recently purchased a blue hydrangea and was told I would need add acid to the soil to keep it blue. When and how should I do this?
|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 alkaline, add aluminum sulfate to the soil in February or March and this summer's blooms should be blue.