Answer: Nikko Blue hydrangeas have coloring that responds to soil pH. In an acidic soil (lower pH) they will have the best blue, in an alkaline soil (higher pH) they will turn pink.
To maintain a good blue, routinely use a fertilizer for acid loving plants such as Hollytone per the label directions beginning next spring. Also use an acidic mulch such as pine bark year round. Avoid using lime near the plant, and do not plant it near a concrete sidewalk or foundation as these can leach lime, especially when new.
Run some basic soil tests to see what the natural soil pH is. Your local county extension can help you with the tests and interpreting the results with an eye on growing hydrqangeas. In your area I would expect it to be naturally acidic.
If it is acidic, your plant should stay blue. If it is neutral or alkaline, you may need to gradually add sulfur to lower the pH. Read and follow the label directions and allow time for the sulfur to take effect. Please do not use aluminum sulfate as this can be toxic to plants if it builds up in the soil. Changing soil pH is best achieved slowly over a period of several years if you need to make a big change.
Enjoy your hydrangea!
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