You can change the color of the blooms of many varieties of Hydrangeas by adjusting the soil pH (a measure of how acid or alkaline the soil is). Many Hydrangeas will have blue flowers when they are growing in an acidic soil. To help produce blue flowers drop the soil pH by using Aluminum sulphate, Sulfur or Ironite. To change the blooms of a Hydrangea to a pink or rose color you can broadcast Hydrated Lime or Dolomitic Lime around them and water in. Our soils are acidic in our area and pH adjustment for flower color will often have to be repeated in the future because the soil returns to a more acid condition over time.