One of the marvelous features of many hydrangea varieties is that the color of the blooms can be manipulated with the right care and know how when it comes to the pH of your soil. With a high pH in the soil between 6.0 and 6.2, your hydrangeas should be blooming in luscious shades of pink. If you're noticing a slip in color, however, and your bright pink blooms are fading, then you'll want to take action to keep your pink hydrangeas from turning white.
Test the pH of the soil where your hydrangea is planted in the spring to see how far away from 6.0 to 6.2 you are on the scale. Add 2 to 4 oz. of dolomitic lime around the base of your hydrangea to help keep your plant blooming pink. This dose can be repeated after three weeks if your pH test showed a result of 5.5 or lower.
Maintain the high pH needed throughout the year by reapplying 2 oz. of lime to the surface around your plant in the beginning of summer and then again in the fall. Each year you can add 2 oz. of lime at the beginning of the spring, summer and fall seasons to keep the pH levels consistent.
Prune your hydrangea in early spring to rid it of old, dead or damaged branches. Sometimes a decrease in the intensity of your pink flowers can be mistaken for turning white and a little pruning can revive the vibrancy of the blooms.
Feed your hydrangea each spring with a fertilizer high in phosphorus such as a 25-10-10. The phosphorus will keep the pH from slipping, and annual feeding should encourage lush growth and large blooms.