04/08/2026
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Gardeners have a color choice only with bigleaf and mountain hydrangeas, which can be pink, purple, or blue. Bloom color and intensity depends on the specific cultivar, weather condition, soil pH, and the aluminum content in the soil. Aluminum availability is determined by the soil pH. Gardeners can adjust the soil pH to influence color.
In soils with a pH of 5 to 5.5, flower color is blue. In less acidic soils, or those with a pH of 6 to 6.5, flower color is pink. Soil with a pH of between 5 and 6 may produce rose to purple flowers, depending on the hydrangea species.
A quick way to influence soil pH for an individual plant is to apply a liquid soil drench. To make pink flowers turn blue, dissolve 1 tablespoon of aluminum sulfate in a gallon of water and drench the soil around the plant in March, April, and May. To make blue flowers turn pink, dissolve 1 tablespoon of hydrated lime in a gallon of water and drench the soil around the plant in March, April, and May. Do not increase the amounts of the color change additives. Aluminum in high doses will harm hydrangea plants. Be careful when applying and do not get these chemicals on the leaves.
The more practical and long-term method of color change is to make a fall application of either 1 cup dolomitic lime per 10 square feet or 1/2 cup sulfur per 10 square feet.
Ultimately, cultivar selection and care determine the outcome. Remember that white-flowered cultivars do not respond to the pH of the soil. Occasionally, however, white-flowered cultivars will sport a pink or blue eye, depending on aluminum availability.
Learn more: https://extension.msstate.edu/publications/hydrangeas-for-mississippi-gardens