Proper hydrangea care begins by choosing a variety that is within the area's cold-hardiness temperature range. Select a suitable, well-drained spot ranging from full sun to deep shade, depending on the selected hydrangea's light requirements. Best planted in early summer or fall, hydrangeas are vigorous growers that require adequate space to mature without vigorous pruning. Once planted, hydrangeas require regular watering for two years until they have established a mature root system.
Hydrangea pruning should only be done immediately following bloom time to avoid harming the next year's flower buds, which form in late summer. Pruning should include both the removal of faded flowers and weak or extraneous shoots to encourage additional branching and fullness.
Hydrangeas in acidic soils with a pH in the 5.5 range produce blue flowers because acidic soils allow aluminum, which produces the blue color, to be taken up into the plant from the soil. This aluminum is not available to hydrangea plants in alkaline soils with a pH in the 7.0 range, so the bloom color is pink. To amend this alkalinity, mix 1 tablespoon of aluminum sulfate in 1 gallon of water, pour the solution around the plant in early spring, and the resulting blooms are blue. To change the bloom color from blue to pink for hydrangeas growing in acid soils, mix 1 tablespoon of hydrated lime in 1 gallon of water, and apply it around the hydrangeas in early spring. With either drench, hydrangea leaves must be kept dry to minimize foliar damage.
Fertilize hydrangeas in late spring and mid-summer with a slow-release, balanced fertilizer, allowing the plants' preparation for winter dormancy to begin in August. A 3-inch layer of organic mulch provides moisture retention while discouraging weed growth.