I am often asked about pruning Hydrangeas, so I thought this might be some good information to share with everyone:
Big pink or blue blooms are Hydrangea macrophylla and just need a slight trim after flowering, never prune in winter or spring as they set their buds the year before.
Round white or pink blossoms like Annabelle or Invincibelle are Hydrangea arborescens. Prune these in late winter or early spring. They bloom on the current season's growth.
Cone-shaped white or pink blossoms, light the Limelight, are Hydrangea paniculata. These also bloom on new wood(current season's growth), so prune in late winter or early spring.