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The proper care of a hydrangea depends on the type of hydrangea you choose. There are approximately 23 species of hydrangeas. However, there are many cultivars grown as ornamentals across the globe. Although several species of hydrangeas are available, there are a couple of species that dominate in popularity.
Even though there will be some differences in specific habitat conditions, most hydrangea species have the same general preferences. Although specific differences in care are relatively minor, they usually concern the amount of water needed, fertilization requirements and shade tolerance. Hydrangeas generally prefer moist, well-drained, fertile soil and tolerate sun or part-shade. Most hydrangeas are hardy and once established and able to recover from moderate stresses.
Hydrangea macrophylla is one of the most common and popular ornamental species. Known as the big leaf hydrangea, this species and its cultivars have one of two types of flower clusters. There are mopheads, which have large globe-shaped flower clusters and lacecaps (Hydrangea macrophylla var. macrophylla), which have several flowers around the edge of the flower cluster with many smaller flowers in the center. Flower colors for this species come in shades of blue, pink and white, depending largely on soil pH and aluminum content. Higher pH produces pink flowers, while lower pH and increased aluminum gives blue flowers. Because this species is usually grown for its flowers, make sure it gets at least four hours of morning sun. Take more care in maintaining moist soils with this species as it is more susceptible to wilting. Additionally, wilting leaves will often fall off which affects its appearance. Fertilize with a general-purpose fertilizer during the summer, but not after August.
Another popular hydrangea species is Hydrangea paniculata. The popularity of panicle hydrangea is partly due to its greater reliability in colder climates than other species. The more elongated flower clusters are white or pink. Some cultivars of this species grow tall enough to be pruned into tree form. Although moist soil is best, this species requires no special care and is the hardiest of the three common species. Supplemental fertilization is not required unless planted in poor soil.
The North American native oak-leaf hydrangea (Hydrangea quercifolia) is another popular hydrangea. This species is deciduous, as are most of the landscape hydrangeas, with white flowers on elongated clusters. This species performs better in shade than some of the other hydrangea species. As with the other species, it prefers moist soils. Oak-leaf hydrangea will tolerate dry conditions but may not flower as a result. You don't need to add supplemental fertilizer, unless it is planted in poor soil. - Most species of hydrangea do not require pruning, and most do not respond well to it. If you decide to prune, focus on just a few entire stems to maintain shape and reduce branch crowding. It is a misconception that all flowering plants require pruning for adequate flowering. When in doubt, only remove dead flower heads.
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Hydrangeas are typically considered to have few pest and disease problems. Most diseases are associated with the foliage but can include bacterial wilt, bud blight, powdery mildew and leaf spots. Most of the pests are piercing-sucking pests, such as aphids, scale and spider mites. Other pests and diseases that occur are nematodes and root rot. All of these problems are infrequent.
Control the common foliage diseases with fungal sprays applied during the first signs of disease occurrence. Create space between plants to reduce fungus favoring humidity. Additionally, clean up diseased leaves lying on the ground, because they can be a source of infecting spores. Control root disease by maintaining adequate soil moisture to prevent weakening low-water stress and preventing excessive soil moisture which can lead to root fungus proliferation.
Control insect pests with systemic insecticides. Systemics will move internally in the plant and the insects will in turn feed on the insecticide. Also, maintain plant health so plants can recover from insect attack. Insects feed more heavily on stressed plants.
