Hydrangea plants produce large flowers ideal for use in fresh and dried flower arrangements. The pH of the soil determines if bigleaf hydrangea flowers are blue or pink. Some bigleaf hydrangea varieties have lower pigment and white blooms. These will remain white even if you adjust the pH of the soil. The most common color change hydrangea growers seek is from pink to blue.
Test the pH of your soil using a soil test kit. A low pH level (6.5 or below) indicates absence of aluminum in the soil. Blue hydrangea flowers need higher pH than pink ones.
You can add aluminum sulfate to the soil if a hydrangea had blue flowers when you planted it and it now has pink flowers. Follow the directions on the aluminum sulfate package carefully. Garden stores have fertilizers designed specifically for growing blue hydrangeas.
Make the flowers of a blue-blooming hydrangea turn purple or pink by adding agricultural lime to the soil. Follow the directions on the package. Lime decreases the soil pH. This is not as easy as increasing soil pH to turn pink flowers blue. Add 4 ounces of lime to start the color change to pink. Repeat the lime application until you get the color you want. It is difficult to block aluminum absorption.