Does Weather Affect Hydrangea Color?

Hydrangea Varieties

• A hydrangea's color is partially dependent on the variety. Smooth hydrangeas (Hydrangea arborescens), such as "Annabelle" (Hydrangea arborescens "Annabelle") and "Grandiflora" (Hydrangea arborescens "Grandiflora"), thrive in U.S. Department of Agriculture plant hardiness zones 4 through 9 and produce white flowers only. Panicle hydrangea (Hydrangea paniculata), which grows in USDA zones 3 through 8, and oakleaf hydrangea (Hydrangea quercifolia), which is found in USDA zones 5 through 9, also produce white to cream blooms that fade to greenish brown. Only bigleaf hydrangeas (Hydrangea macrophylla), also known as French hydrangeas, vary in color from pink to blue.

Soil Conditions

• The color of bigleaf hydrangeas is based upon the availability of aluminum in the soil. Hydrangeas can access and use aluminum only in acidic soils, which turns the blossoms blue. Flowers are pink in alkaline soils, indicating that the plant is not receiving adequate aluminum. Hydrangeas tolerate both acidic and alkaline soil, as long as the soil is rich in organic matter, drains well and receives adequate moisture.

Changing Colors

• So your hydrangeas are blue, but you'd really prefer pink, or vice versa. You can change the color of your hydrangeas with a little manipulation. To change blue hydrangeas to pink, sprinkle 3 cups of dolomitic lime around the base of the plant in the spring. Make a second application in late fall. The process of changing pink hydrangeas to blue is just as simple. Drench the soil around the hydrangea with a solution of 4 tablespoons aluminum sulfate diluted with 1 gallon water. Repeat this process in three to four weeks. Dolomitic lime raises the soil pH, while aluminum sulfate lowers it. Keep in mind that the flowers might not change color until the following summer. Use these products cautiously. Use only dolomitic lime, because other lime products are caustic and can cause burns. Aluminum sulfate can damage the soil if used excessively.

Growing Conditions

• Hydrangeas grow best in partial shade, especially in hot climates. Morning sun, followed by afternoon shade, is usually ideal. In full sun, the blossoms may fade or even become tinged with brown. Drought can have similar negative effects. For best color, plant hydrangeas where they get dappled shade and keep the soil consistently moist, but not soggy.