Prune hydrangeas only in the summer before August to be safe. Some gardeners says that hydrangeas can be pruned even into August, but this might be risky. Note that pruning is not the same thing as removing the dead blooms, there are certain things to consider before pruning, remove all dead stems from hydrangeas every year. Prune about 1/3 of the older stems only if the plants are at least 5 years old. If you want to reduce the size of the plant then it may be cut back in June or July with harming the next year's bloom.

Removing dead stems is the only pruning that must be done for the health of the plant and these can be removed any time of the year. Dead blooms can also be removed at any time. Remember if your hydrangea is getting much too large or old, you must prune it.