Hydrangeas are a genus of popular ornamental shrubs known for their abundant and long-lasting flowers. These deciduous plants display a wide range of sizes, shapes, and colors, making them versatile in garden design. The most commonly cultivated types differ significantly in appearance, hardiness, and care requirements. Understanding these differences helps in selecting the right plant for a specific location.
Bigleaf Hydrangeas (Hydrangea macrophylla)
The Bigleaf Hydrangea, originating in Japan, is the most recognized type, known for its large, glossy leaves and two distinct flower head forms. The Mophead variety features large, globe-shaped clusters composed almost entirely of showy sterile florets. The Lacecap variety displays a flatter flower head with a ring of larger, sterile florets circling a center of tiny, fertile flowers.
A unique feature is its ability to change flower color based on the soil’s chemistry and the availability of aluminum ions. Acidic soil (pH below 6.5) allows aluminum absorption, resulting in blue or purple flowers. Alkaline soil (pH above 7.5) restricts absorption, leading to pink or red blooms. White-flowering cultivars do not exhibit this color shift.
This species is typically the least cold-tolerant because it forms flower buds on “old wood.” These buds are susceptible to damage from late spring frosts, which can prevent blooming. Modern reblooming cultivars produce flowers on both old and new wood, offering a more reliable bloom cycle.
Panicle Hydrangeas (Hydrangea paniculata)
Panicle Hydrangeas are recognized by their large, cone-shaped or pyramidal flower clusters, which can reach lengths between 6 to 16 inches. These substantial inflorescences give the shrub an upright texture. The flowers emerge in summer as white or lime green and gradually transition to shades of pink, red, or bronze as the season progresses into fall.
This color change is a natural aging process independent of the soil’s pH or aluminum content. The Panicle Hydrangea is one of the most rugged and cold-hardy species, thriving where Bigleaf varieties often struggle. They are reliable bloomers because they form flower buds exclusively on the current season’s growth (“new wood”).
Their superior hardiness and ability to tolerate more direct sun exposure make them adaptable to a wider range of garden conditions. Popular cultivars include the large ‘Limelight,’ the compact ‘Little Lime,’ and the early-blooming ‘Quick Fire.’ This species is often trained into a single-trunk small tree form for landscape design.
Smooth Hydrangeas (Hydrangea arborescens)
The Smooth Hydrangea is a deciduous shrub native to the eastern United States, often found growing in wooded slopes. The plant typically reaches 3 to 5 feet and spreads by underground stolons, forming colonies. It is known for its large, rounded flower heads, which are typically white or greenish-white.
Some newer hybrids produce pink flowers. This native species is extremely reliable because it produces flowers entirely on new wood. This trait makes it cold-hardy and allows for severe pruning in late winter without sacrificing summer blooms.
Cultivars such as ‘Annabelle’ are known for their massive, sometimes floppy, flower heads that can reach up to 12 inches across. ‘Incrediball’ features stronger stems to better support the weight of the blooms. Unlike the Bigleaf Hydrangea, the flower color of H. arborescens is stable and is not affected by soil pH.
Oakleaf and Climbing Varieties
The Oakleaf Hydrangea (Hydrangea quercifolia) is native to the southeastern United States and easily identified by its deeply lobed foliage, which resembles that of an oak tree. The flowers are borne in upright, conical panicles, starting white and aging to pink or mauve.
This species offers multi-season appeal. Its leathery leaves turn rich shades of burgundy, red, and bronze in the autumn, providing exceptional fall color. The older stems reveal attractive cinnamon-brown bark that peels, adding winter interest.
The Climbing Hydrangea (Hydrangea anomala petiolaris) is a vigorous woody vine rather than a shrub. It uses aerial roots to cling and climb up vertical surfaces like walls or tree trunks. While slow to establish, it can eventually reach heights of 30 to 50 feet, suitable for covering large structures.
Its flowers are flat, lacecap-style clusters of fragrant white blooms, surrounded by showy sterile florets. The mature vines also feature attractive, reddish-brown exfoliating bark, providing ornamental value during winter. If no vertical support is present, the Climbing Hydrangea will sprawl along the ground, forming a dense, mounding shrub.