With proper care and placement, hydrangeas should bloom reliably year after year, rewarding the gardener with the huge, showy flowers that has made the plant a beloved fixture in many gardens. Because incorrect pruning is the main cause of failure to bloom, it is essential to know what type of hydrangea you have, as this will dictate if and when you should prune your shrub. The vast majority of hydrangeas sold in commercial nurseries are bigleaf, or French, hydrangeas (Hydrangea macrophylla), though oakleaf (H. quercifolia) and smooth (H. arborescens) have also lately gained in popularity. French and oakleaf should be pruned immediately after flowering, while smooth hydrangea can be pruned during dormancy in the winter or spring.
Identify Your Hydrangea
Inspect the plant's leaves. Bigleaf hydrangea leaves are large, from 4 to 6 inches in length, oval-shaped and with serrated edges. Smooth hydrangea leaves can easily be confused with bigleaf hydrangea leaves. Oakleaf hydrangea leaves, as the name implies, strongly resemble oak leaves, though they are much larger and feel velvety to the touch.
Determine the growth habit of your hydrangea. Bigleaf hydrangeas grow to be large, 5 to 8 feet, and have a rounded form with many stems, called canes, emerging from the ground at the base of the plant. New growth is greenish, while older canes are brown or gray with a papery texture.
Oakleaf hydrangea grows to between 6 and 8 feet tall and has papery red bark.
Smooth hydrangea usually stays between 3 and 5 feet tall and has a rounded form.
Try to recall if the hydrangea in question has ever flowered. If the flowers were blue or pink, the hydrangea is probably a bigleaf. If the bush produced very large, heavy spheres of white flowers, the shrub is probably a smooth hydrangea. White, cone-shaped sprays of flowers are easily identifiable as oakleaf hydrangea blooms.
Note the time of year. Never prune bigleaf and oakleaf hydrangeas after midsummer; never in spring, fall or winter, because this will remove the old wood shoots the shrub requires to produce new flower buds. Prune smooth hydrangea in fall or winter.
Prune the hydrangea at the appropriate time of year by cutting back branches to the strongest buds below the tip of the branch. For oakleaf and bigleaf hydrangeas, this should be no more than 1 foot down; smooth hydrangeas will benefit from more aggressive pruning.
Thin out old and dead branches from the center of the hydrangea by cutting the canes back at the ground. Improved airflow will help stimulate healthy growth and flowering.
Caring for Your Hydrangea
Ensure the shrub is receiving adequate amounts of water, especially during the hot summer months. The root of the plant's Latin name, hydra, is a hint that this shrub is an especially thirsty species. Leaves and flowers wilt easily when the plant is overheated or dehydrated, and are a sure sign that the plant is in immediate need of water.
Apply mulch around the base of the hydrangea to help keep the roots cool and moist.
Make sure the hydrangea is located properly. While most plant information sources claim hydrangeas do well in full sun, plants perform best when they receive morning sun but some shady protection from the hot afternoon sun of summertime.
Fertilize with an all-purpose fertilizer, such as an 8-8-8 or 10-10-10. Fertilizing not only feeds the plant and helps it develop rich foliage and flowers, but also helps acidify the soil--a must for the acid-loving hydrangea species. Healthy plants are also far less susceptible to attacks by insects or disease, which can stress the plant and prevent it from flowering.