Nikko Blue Hydrangea

Nikko Blue is the hydrangea people picture when they picture hydrangeas. Hydrangea macrophylla 'Nikko Blue' carries large rounded mophead flowers in a deep true blue, on a dense shrub 4 to 6 feet tall and wide, hardy from Zone 6 through Zone 9 in part sun to part shade. It grows quickly and reaches full size in three or four seasons.

Bloom comes in early to midsummer and holds for weeks, opening blue and aging through soft purple and green. The heads dry well on the plant and cut well fresh.

The color of the blooms depends on your soil. Acidic soil, roughly pH 5.5 and below, gives the deep blue this variety is named for. Neutral to alkaline soil turns the same flowers pink or mauve. Aluminum sulfate applied in spring pushes color toward blue, and soil sulfur does it more slowly but lasts longer. If your ground runs alkaline and you want blue, a container is the easier answer.

Classic varieties of bigleaf hydrangea like this one bloom on old wood, so the buds form the previous summer and sit on the stems through winter. Do not cut it back in spring, and expect a light year after a hard freeze or a late frost. Give it morning sun with afternoon shade, consistent moisture, and shelter from cold wind. The leaves wilt on hot afternoons and recover by evening, so check the soil before watering again.