The Q&A Archives: Sister Teresa Wrong Color

Question: We planted (3) Sister Teresa Hydrangeas (Hydrangea Macrophylla) last May along with other white flowering shrubs, perennials and annuals. They are in part shade. Two are planted next to each other with a boxwood on each side. The other one is between juniper and azaleas. When they started to bloom they were pink not white. The nursery suggested Miracid; I gave one dose but they started to turn light purple. The nursery not able to find anything on how to turn them white (thought maybe they were mistagged). Do you have any suggestions - do we need more Miracid or a different treatment?

Answer: Unfortunately I have not seen this plant myself and am unable to find a standardized description of it, although it is occasionally offered for sale. I am wondering if this is a case of a bloom that is described as "near white" or as "fading to white" rather than as straight white. Hydrangea blooms color can be affected by soil pH, as you saw when you used the Miracid. 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. I do not know of any treatment you could use to turn the blooms white with a possible exception of keeping the soil pH somewhere in between the two and causing any color to possibly fade. If you really want a white hydrangea you might look into the H. arborescens varieties such as "Annabelle" which is truly white naturally.

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