How can I get pink or blue hydrangeas?

The pH of your soil is what determines the color of hydrangea blossoms, and you can alter the pH to get the result you want. For blue flowers, the pH has to be between 4.5 and 5.5. For pink flowers, you must raise the pH to between 7.0 and 7.5 by liming the soil. If you thought you were growing blue hydrangeas and some came out pink, a nearby concrete foundation may be the culprit.