Hydrangea

Hydrangea arborescens

Hydrangeaceae · broadleaf deciduous shrub · introduced

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This profile synthesizes data from multiple published sources. Expert field review is in progress.

Smooth hydrangea blooms on new wood, prune in late winter, and that is the most important thing to know. 'Annabelle' is the ubiquitous cultivar and it performs well in shade across the Puget Sound lowlands. The plant is native to eastern North America but adapted to our conditions. The main limitation is drought: smooth hydrangea wilts dramatically when soil dries out in July and August, and repeated wilting degrades the plant over time. In our region, site it where it gets consistent moisture or plan to irrigate. Part shade to full shade is ideal; full sun works only with reliable water. Root weevil is the primary pest. Powdery mildew is cosmetic. The newer selections like 'Incrediball' have stronger stems that hold up the flower heads better than classic 'Annabelle' in rain.

— Chris Welch, ISA Certified Arborist

Smooth hydrangea (Hydrangea arborescens, Hydrangeaceae) is a loosely branched deciduous shrub native to eastern North America from New York to Florida and west to Oklahoma, reaching 3 to 6 feet tall (occasionally 10 feet). Large white flower heads bloom from May through July. Fall color is yellow.

Smooth hydrangea grows in part shade (tolerates full sun with consistent moisture) on moist or rocky soils, hardy in Zones 4a to 9b. It blooms on new wood; prune hard in late winter. Disease pressure is notable, with 13 documented associations including powdery mildew, leaf spot, and botrytis blight. Root weevil and foliar nematode are the primary pests. The cultivar 'Annabelle' (large white mophead, 6 feet) is the dominant selection.

Quick Facts

Height
9 ft
Spread
6 ft
Growth Rate
Medium
Light
Sun to Part Shade
Soil
Moist
Water
Moderate
Hardiness
Zone Zones 4a–9b
Bloom Time
June to September

Diseases (12)

Pests (2)

Cultivars (4)

'Annabelle'
Common name: Smooth Hydrangea; Mature height: 6 ft
'NCHA4' Incrediball
Trade name: Incrediball. Bred by Thomas Ranney at NC State University as an Annabelle improvement. Flower heads comparable to or larger than Annabelle (up to 12 inches across) held on stronger, thicker stems that do not flop under rain or sprinkler water. White at opening, aging to jade-green. 4-5 ft tall and wide.
The first-pick recommendation when Annabelle's stem flop is a problem on a site. Same old-wood/new-wood flexibility as Annabelle (blooms on new wood, prune hard in late winter).
'NCHA5' Invincibelle Spirit
Trade name: Invincibelle Spirit (and improved Invincibelle Spirit II). Bred by Thomas Ranney at NC State University. The first pink-flowered smooth hydrangea selection. Pink mophead flowers 4-6 inches across, held upright on strong stems. 3-4 ft. Part of the Breast Cancer Research Foundation fundraising program.
Choose when pink flower color is the selection driver and an arborescens habit is wanted (smaller, more refined than a bigleaf mophead).
''Haas' Halo''
Lacecap form of smooth hydrangea (rather than the mophead transformation seen in Annabelle and Incrediball). Flat white flower heads up to 14 inches across with a central disk of fertile flowers surrounded by large sterile florets. 5-6 ft. Strong stems, does not flop.
Pick when the pollinator value of the fertile center flowers matters and a wilder, less formal look is wanted than the Annabelle/Incrediball mophead.