Nikko Blue Bigleaf Hydrangea Hydrangea macrophylla 'Nikko Blue' Description Blooms blue globular flower. Flowers will turn blue when Aluminum Sulphate is added to the soil. Flowers bloom on old wood. Dark green foliage.Bloom Period: Mid-summer until frostGrowth Habit: Upright and roundedMature Height: 3' to 4' (90 cm to 120 cm)Mature Spread: 3' to 4' (90 cm to 120 cm)Growth Rate: Moderate More Details Sun Exposure: Full morning sun to partial shadeCold Hardiness Zone: 4Cut or dried flowerLong bloomingPruning Tip: Do not prune, only remove spent flowers and dead/damaged stemsLandscape use: Foundation planting or garden accent