Incrediball® Hydrangea arborescens 'Abetwo'
Incrediball hydrangea is an improved Annabelle hydrangea. It looks almost identical but the stems are extremely sturdy and won't flop over like the Annabelle hydrangea.
Very hardy, zones 3-8
Height: 4 - 5 feet
Width: 4 - 5 feet (space 4 to 6 feet apart)
Blooms: early summer to fall
Dimension of blooms: as much as 12" across
Foliage: dark green, serrated edges
Growth habit: mounded
Soil: moist, well-drained
Incrediball blooms on new wood and benefits from pruning in early spring. Flowers open green, turn white before maturing to green again.
This would be my choice for a white mophead hydrangea as it is sturdy enough to hold the blooms erect while providing masses of balls of white clustered flowers. It is similar in height and width to Annabelle as well.