The Q&A Archives: hydrangea

Question: how do you keep them blue,and how do you change them to white,how big will they get?

Answer: 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. You cannot turn a blue or a pink hydrangea white. 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. Depending upon the kind of hydrangea you plant, it can grow upwards of 6' in height and 12' in width before being so overgrown the branches flop to the ground. Hope this answers all your questions!

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