Hydrangeas, often affectionately known as “ortencias” in various regions, are celebrated garden plants. Their large, vibrant flowerheads bring elegance and charm to any landscape. These versatile shrubs offer a diverse range of forms and colors, captivating observers with their beauty.
Understanding Hydrangea Varieties
Numerous Hydrangea varieties exist, each with distinct characteristics influencing their appearance and cultivation needs.
Bigleaf Hydrangea (Hydrangea macrophylla) is widely recognized for its large, globular “mophead” or flat “lacecap” blooms. These typically grow 3 to 10 feet tall and wide, preferring morning sun and afternoon shade, with blooms appearing from summer into autumn.
Panicle Hydrangea (Hydrangea paniculata) is a robust variety, often reaching 8 to 15 feet in height, with some cultivars growing even larger. Its cone-shaped flowers emerge white, gradually transitioning to pink or burgundy as they mature, blooming from mid-summer into fall. This type tolerates more sun than Bigleaf Hydrangeas and is quite adaptable.
Smooth Hydrangea (Hydrangea arborescens), sometimes called ‘Annabelle’, features large, rounded clusters of white or sometimes pink flowers. It typically grows 3 to 5 feet tall and wide, thriving in full sun to partial shade, with blooms appearing in summer.
Oakleaf Hydrangea (Hydrangea quercifolia) stands out with its distinctive, deeply lobed leaves that resemble oak leaves, which turn a rich wine-red in autumn. This variety produces elongated, conical white flower clusters in summer, maturing to pink. It can reach 6 to 8 feet in height and width, preferring partial shade.
Climbing Hydrangea (Hydrangea anomala petiolaris) is a woody vine that can ascend structures up to 50 feet, attaching itself with aerial rootlets. It bears flat, white lacecap flowers in early summer and is well-suited for shady locations.
Essential Hydrangea Care
Proper light exposure is crucial for Hydrangea health and bloom production. Bigleaf Hydrangeas generally perform best with morning sun and protection from intense afternoon sun, especially in warmer climates. Panicle and Smooth Hydrangeas can tolerate more direct sunlight, with Panicle Hydrangeas even thriving in full sun in cooler regions. Oakleaf and Climbing Hydrangeas prefer partial to full shade, benefiting from protection from the harshest midday rays.
Hydrangeas prefer well-draining soil that is rich in organic matter. A slightly acidic to neutral soil pH is generally suitable, though Bigleaf Hydrangeas are unique in their color response to soil acidity. When planting, dig a hole twice as wide as the root ball and just as deep, ensuring the top of the root ball is level with the ground. Backfill with soil, gently firming it around the roots to remove air pockets.
Consistent watering is important, particularly during dry periods and for newly planted specimens. Hydrangeas are known to be “water thirsty,” so ensure the soil remains consistently moist but not waterlogged. Deep watering two to three times a week during hot, dry weather helps establish a strong root system. Once established, some varieties, like Oakleaf Hydrangeas, become more drought-tolerant.
Fertilization can promote vigorous growth and abundant blooms, though it is not always necessary. A balanced, slow-release granular fertilizer applied in early spring can provide nutrients throughout the growing season. Avoid over-fertilizing, as this can lead to excessive foliage growth at the expense of flowers. Applying compost or organic mulch around the base of the plant in fall can also supply nutrients naturally.
Changing Hydrangea Bloom Color
The captivating color of Bigleaf Hydrangea (Hydrangea macrophylla) blooms is directly influenced by soil pH. Acidic soil, with a pH of 5.5 or lower, typically results in blue flowers. As the soil becomes more alkaline, with a pH of 6.5 or higher, the blooms tend to be pink. A neutral soil pH, between 5.5 and 6.5, can produce purple or mixed-colored flowers.
To encourage blue blooms, gardeners can amend alkaline soil by adding aluminum sulfate or elemental sulfur. These amendments lower the soil pH, making aluminum more available to the plant, which is responsible for the blue pigment. Conversely, to promote pink blooms, agricultural lime can be added to increase soil alkalinity. It is important to note that white-flowering Bigleaf Hydrangeas do not change color regardless of soil pH, as they lack the specific pigment compounds that react to aluminum.
Pruning for Health and Blooms
Pruning Hydrangeas correctly depends on whether they bloom on “old wood” (previous year’s growth) or “new wood” (current year’s growth).
Bigleaf (Hydrangea macrophylla) and Oakleaf (Hydrangea quercifolia) Hydrangeas bloom on old wood. These varieties should be pruned immediately after flowering in late summer to avoid removing next year’s flower buds. Focus on removing dead, damaged, or weak stems, and thin out overcrowded branches to improve air circulation.
Panicle (Hydrangea paniculata) and Smooth (Hydrangea arborescens) Hydrangeas bloom on new wood. This allows for more flexible pruning, typically done in late winter or early spring before new growth emerges. These types can be pruned more aggressively, cutting back stems to promote strong new growth and larger flower heads. Removing about one-third of the plant’s height and thinning out older, weaker stems is a common practice. Climbing Hydrangeas generally require minimal pruning, primarily to control their size or direct their growth, and this is best done after flowering.
Addressing Common Hydrangea Problems
A common concern for gardeners is a lack of blooms on their Hydrangeas. This can stem from several factors, including improper pruning that removes flower buds, insufficient sunlight, or late spring frosts damaging new growth. Ensuring the correct pruning time for the specific Hydrangea variety is essential, as is selecting a planting site with adequate light exposure. Protecting tender new growth from unexpected late frosts can also help preserve future blooms.
Hydrangeas can occasionally be affected by pests such as aphids or spider mites, particularly in stressed plants. A strong spray of water can dislodge many soft-bodied pests, and for more persistent infestations, horticultural oil or insecticidal soap can be effective. Fungal diseases like powdery mildew or leaf spot may appear, especially in humid conditions or areas with poor air circulation. Ensuring good air flow around plants and avoiding overhead watering can help prevent these issues.
Leaf discoloration beyond the typical pH-induced color changes can indicate other problems. Yellowing leaves with green veins, known as chlorosis, often suggest an iron deficiency, which can occur in alkaline soils. Adjusting soil pH or applying an iron supplement can resolve this. Brown, crispy leaf edges or scorched leaves can result from too much direct sun, particularly afternoon sun, or insufficient watering during hot periods. Providing afternoon shade or increasing watering frequency during heat waves can mitigate sun scorch.