The hydrangea macrophylla, which is native to Korea and Japan, includes varieties such as Bigleaf, French, Lacecap, Mophead, Penny Mac and Hortensia. These shrub-like varieties, surrounded by large, serrated foliage, produce large, round bloom clusters in white, green, pink, purple or blue, depending on the soil that supports them. Modifying the pH level of the soil--making it more alkaline or more acidic--can alter the color of the bloom.
Take soil samples from the planting location and have them tested by your local agricultural extension agency or other soil testing laboratory in the area. For the best growth, regardless of color, the soil pH should be between 5.5 and 7.0.
Create pink blooms by increasing the alkalinity of the soil. At least four to six months before the blooming cycle begins, sprinkle 3 to 8 cups of dolomitic lime around the base of the hydrangea plant. Subsequent waterings will deliver the lime down into the root system to begin increasing the pH level.
Apply dolomitic lime, at the same rate, two to three more times in the late fall and mid winter. For the best pink colors, the soil pH should be at a range of 7.0 to 7.5.
Apply a phosphorous-rich fertilizer to hydrangea plants in order to prevent aluminum from entering the root system. Follow the manufacturer's directions with regard to application dosage and schedule.