The genus Hydrangea encompasses dozens of species of flowering shrubs, often colloquially known as Hortenzia, particularly referring to the popular Bigleaf Hydrangea (H. macrophylla). These deciduous plants are highly valued in landscapes for their enormous, colorful flower clusters that bloom from summer into fall. Hydrangeas thrive in many temperate climates, but understanding the specific needs of each species is essential for successfully growing a healthy, blooming plant.
Establishing the Plant: Siting and Soil Preparation
The most favorable location for planting hydrangeas provides a balance of sunlight and shade throughout the day. Most varieties thrive best when they receive direct morning sunlight, followed by protective shade during the scorching afternoon hours. Placing the plant beneath a deciduous tree canopy or on the east side of a structure prevents leaf scorch and excessive wilting.
Hydrangeas require rich, well-draining soil, as they do not tolerate “wet feet.” Saturated soil can lead to root rot, a common issue for these shrubs. To prepare the planting area, incorporate organic matter, such as compost, to improve both drainage in heavy clay and moisture retention in sandy soil. When planting, the hole should be two to three times wider than the root ball but no deeper, ensuring the top of the root ball is level with the surrounding soil surface.
Essential Ongoing Maintenance
Consistent moisture is the most important factor for hydrangea health, a trait reflected in the plant’s Greek name, which means “water vessel.” Hydrangeas wilt dramatically when stressed by heat or drought, especially H. macrophylla and H. arborescens. Providing a deep watering of about one inch per week, delivered directly to the base, encourages deep root growth and is more effective than light, frequent sprinkles.
Applying a two-to-three-inch layer of organic mulch, such as shredded bark, around the base is highly beneficial. This layer insulates the soil, keeping the root zone cool, and significantly reduces water evaporation. Fertilization should be approached cautiously, as too much nitrogen encourages foliage growth at the expense of flower production. A balanced, slow-release fertilizer, such as a 10-10-10 formulation, applied once in early spring as new growth begins, is generally sufficient for established plants.
Specialized Care: Pruning and Color Manipulation
Pruning hydrangeas correctly depends on whether the species blooms on “old wood” or “new wood.” Old wood bloomers, including Bigleaf (H. macrophylla) and Oakleaf (H. quercifolia), set flower buds on the previous season’s growth. These varieties should only be pruned immediately after flowers fade in mid-summer, allowing time to develop new buds before winter dormancy. Pruning these types in late winter or spring removes all future blooms.
In contrast, new wood bloomers, such as Panicle (H. paniculata) and Smooth (H. arborescens), form flower buds on the current season’s growth. They can be pruned safely in late winter or early spring while the plant is dormant, often resulting in larger blooms and stronger stems. Re-blooming varieties, which flower on both old and new wood, require minimal structural pruning, typically limited to removing dead or damaged branches in the spring.
The ability of Bigleaf and Mountain hydrangeas (H. serrata) to change flower color is controlled by aluminum ions in the soil, regulated by soil pH. Blue flowers develop in acidic soil (pH 5.0 to 5.5), where aluminum is readily available for absorption. To encourage a blue hue, apply soil acidifiers like aluminum sulfate.
Conversely, pink flowers emerge in alkaline soil (pH 6.0 or higher), as the higher pH locks up the aluminum. To shift the color toward pink, garden lime can be incorporated to raise the pH level. White-flowered varieties are an exception, as their color is not affected by soil chemistry and cannot be manipulated.
Protecting Hydrangeas from Pests, Disease, and Winter
Hydrangeas are susceptible to common garden pests, including aphids and spider mites, which feed on the plant’s sap. A strong blast of water can often dislodge minor aphid infestations, while horticultural oil or insecticidal soap is effective for persistent issues. Fungal diseases like powdery mildew, which appears as a white, dusty coating on leaves, are common, especially in humid conditions or where air circulation is poor.
Preventing fungal problems involves avoiding overhead watering, particularly late in the day, so foliage has time to dry before nightfall. Ensuring adequate spacing between plants also promotes airflow, which helps keep leaves dry and reduces disease spread. For winter protection, especially in colder climates where Bigleaf hydrangeas are grown, the flower buds on old wood must be shielded from harsh temperatures and drying winds. A thick layer of mulch, such as 18 inches of straw or shredded leaves, should be applied over the base once the ground freezes, and some gardeners wrap the entire shrub in burlap.