How can hydrangeas be made to change color?
One of the oddities of the plant kingdom is the sensitivity of some hydrangeas to change color according to the pH of the soil. With the pink/blue ‘mophead’ varieties, acid soil pushes the flowers toward blue. You add sulfur or aluminum sulfate to the soil to make the pH acid (do not use aluminum sulfate near azaleas or other plants of the Erica family). If the soil is more alkaline, the flowers tend to be pink. You add lime to the soil to make the pH alkaline.
