Hydrangea macrophylla var. macrophylla 'Blue Danube' is a deciduous shrub that grows 3 to 6 feet tall and wide. It features dark green leaves and large clusters of flowers, which are either lacecap or mophead in structure. Blue Danube is small in structure, growing 4 feet tall and wide, and bearing large, mostly sterile flowerheads, which are deep blue when planted in acidic soil and dark pink when planted in alkaline soil. Heavy flowering and compact, it is ideal for growing in a container in partial shade. The flowers dry well and can be used in arrangements.