Hydrangea
Hydrangea arborescens
Hydrangeaceae · broadleaf deciduous shrub · introduced
Last updated
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.