Answer: The changeable color varieties of hydrangea should be blue in a pH range of about 5.0 to 5.5 and turn pink when the pH is a bit higher, say between 6.0 and 6.5 or so. In your area, the soil may naturally be acidic enough for the hydrangeas to become blue. Blue hydrangeas can be changed to pink by adding 3-8 cups (depending on the size of the plant) of dolomic lime around the base of the hydrangea. Do this 2 or 3 times between the blooming seasons. As an alternative, you can also try a bit of superphosphate around the base of the plant. Shoot for a pH of 6.8-7.2 to turn the flowers from blue to pink.
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