Even though July is the preferred month to prune bigleaf hydrangeas, sometimes circumstances intervene to keep you from doing what should be done.
If that is the case, don’t despair. Hydrangeas can still be pruned after August… but more carefully than in July.
The first job is to shorten by half all of the stems that bear faded flowers. These stems are least likely to have flowers next year. You may find that by removing them your shrub is reduced enough to get by.
If you need to make your hydrangea even smaller, shorten the tallest non-flowering stems.
Try to leave untouched as many twelve to eighteen inch leafy stems on the plant as possible. These are the branches that will produce flowers next summer.