Color Change
White, pink, or blue - the color is up to you. Well, not really. Gardeners only have a color choice with Bigleaf and Serrated Hydrangeas, and several factors may affect the outcome. Bloom color and intensity depend on the specific variety, weather, plant health, and soil. Of these, soil pH is the strongest influence the gardener can adjust.
Blue or pink blooms depend on soil pH and corresponding available aluminum. At lower pH levels (acid soils), aluminum is more readily available to the plant and flowers become blue. At higher pH ranges (more alkaline soils), aluminum is less available and flowers are pink. Want pink flowers? Add lime to raise soil pH. Want blue flowers? Add sulfur to lower soil pH.
Changing soil pH is a gradual process and requires a soil test for accuracy. Broadcast 1/2 cup of wettable sulfur per 10 square feet and water-in to make flowers blue. To make the flowers pink, broadcast one cup of dolomitic lime per 10 square feet and water it into the soil. Raising pH takes longer than lowering. It may be next year before a noticeable change to pink flowers.
A faster option for changing flower color is liquid soil drenches. Want to enhance your blue flowers or to change pink ones to blue? Dissolve one tablespoon of alum (aluminum sulfate) in a gallon of water and drench the soil around the plant in March, April and May. Desire pink flowers? Dissolve one tablespoon of hydrated lime in a gallon of water and drench the soil around the plant in March, April and May. Avoid splashing either of these solutions on leaves, bark, or skin as it can cause burning
Kerry Smith, Horticulture Associate
Jerry A. Chenault, County Extension Agent
Kenneth Tilt, Horticulture Specialist