Hydrangea is a garden favorite. It has lovely blooms and can become a good sized plant. Many ask when should it be pruned or cut back. A good rule of thumb is to understand that Hydrangeas bloom on old wood. As soon as the flowers are spent, as soon as they start to turn brown it is a good idea to prune. This allows a maximum time for the branch to grow, set new wood which will then turn into old wood and produce more flowers.