How To Keep Red Color In Red 'n Pretty Hydrangea - Knowledgebase Question

Temecula, CA
Question by djbixler
March 30, 2001
I know that by adding aluminum sulfate, you can turn or keep some hydrangeas blue. Is there anything I need to add to my soil to keep my Red 'n Pretty hydrangea red or to intensify the red? I just planted one in my camellia/azalea bed which has been amended several times with lots of peat. This bed is also mulched every winter with pine needles from our Christmas tree. The pine needles are turned into the soil every Jan. when we cut up the new tree for mulch. I haven't done a soil test, but I believe that this has created somewhat acidic soil since my camellias and azaleas thrive in this location. By the way, can I expect to see flowers this summer or do hydrangeas need longer to establish themselves before flowering? Thank you!!!! Janette


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Answer from NGA
March 30, 2001

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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. Because you've added peat and pine needles to your soil, the pH will be on the acidic side. Do a soil test and add lime if necessary to sweeten the soil. It's best to apply amendments in February or March of each year so the blossoms will be the color you expect!

Your hydrangea will probably bloom this year (they don't take long to become established!) Enjoy!

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