How to prune bigleaf hydrangea 'nikko blue'

Immediately after flowering (mid to late summer, usually July–August). Cut spent flower heads back to the first pair of healthy buds. Remove up to one-third of the weakest stems at the base to open up the plant; avoid cutting into old woody stems unless necessary.

Annually, right after bloom. Yes — pruning is important but timing is everything. Nikko Blue blooms on old wood, so buds for next year form in late summer. Prune lightly right after flowering ends (typically July–August). Skip heavy autumn cuts entirely or you'll sacrifice next year's blooms. Remove spent flower heads and any weak or dead stems only.

Cut spent flower heads back to the first pair of healthy buds. Remove up to one-third of the weakest stems at the base to open up the plant; avoid cutting into old woody stems unless necessary.