Hydrangeas are a showy perennial flower with broad, veined leaves and large flowers in whites, pinks and blues. Gardeners may alter the color of the blooms by adjusting the levels of the pH, aluminum and lime in the soil around the plant. Over 1,200 varieties of hydrangea exist; they can grow up to 10 feet tall. These plants are perennial shrubs that flower in the summer and require pruning and deadheading.
Plant in late summer or early fall in any zone. Plants are available in many varieties and some are hardy as far north as USDA Zone 3a. Hydrangeas are best grown around Zone 8, where the summers are not too humid and freezing temperatures are not the norm.
Where to Plant
Hydrangeas enjoy moist soil and varying amounts of light depending on climate. Plant hydrangeas in a well-draining soil or compost/soil mix, and keep soil moist, particularly in the summer. Though hydrangeas can take partial-full sun in cooler climates, they need shade in the Deep South, to prevent wilting during the hottest part of the day.
Hydrangeas are available in white, pink and blue color tones. With the exception of the white blooms, colors may be changed by altering the chemical makeup of the soil, though the intensity of a particular color may not be changed. For example, a light pink hydrangea may be changed to light blue, but not deep blue.
Lime for Pink
Adding lime to the soil will change the bloom color from blue to pink. By adding lime, the pH of the soil is increased and the bloom will turn to pink when the pH is consistently in the 6.0-6.2 range. Hydrangeas absorb aluminum, which helps to define the color, and by adding lime, the aluminum absorption is inhibited.
If you desire pink hydrangeas, add lime to the soil 3-4 times per year and fertilize with a high-phosphorous product.
Aluminum for Blue
If you desire blue hydrangeas, add aluminum to the soil by mixing one tablespoon of aluminum sulfate to one gallon of water and apply to the plant and soil. Water the plant well before application to avoid burning the roots. In addition, fertilize with a low-phosphorous product and add organic mulch (coffee grounds or compost) to the soil to help lower the pH and encourage absorption of the aluminum.