Hydrangeas rarely, if ever, need pruning. In some cases, however, your hydrangea can grow too large over time, or just get too old, and you’ll need to prune it accrording to the variety.
Arborescens rebloom every year, and if they need pruning, do so during spring or summer prior to blooming. It’s common to cut these plants only a couple inches from the ground. Be careful not to prune more than this, because the stems may not increase in size from then on.
Unlike arborescens, paniculatas should be pruned in the fall or winter, but can also be done in the spring if necessary. It’s recommended to avoid pruning this variety often, but when you need to, rid the plant of unattractive cross-branches.
Some people prefer to grow paniculatas as trees. If you do, never remove the trunk or top branches. Otherwise, the plant will revert to its normal, shrub-like form unless training is started as soon as the plant’s new shoots appear.
It’s recommended these three varieties be pruned before late summer, in order to avoid interrupting the blooming process for the following year. Interrupting that process will result in little to no bloom. There is no common pruning method for these varieties—only that they should be pruned according to personal preference, as long as stems aren’t removed (removing stems contributes to interruption of the blooming process).
Remove dead stems from your hydrangea on a yearly basis. The older the plant gets, the more you’ll remove live stems, as well. It’s recommended once a plant reaches five years old that 1/3 of the living stems be removed in order for maximum plant revitalization.
Pruning hydrangeas can be harmful to the plant’s blooms, so it’s important to remember when it should be done, according to its variety. After pruning, it’s common for hydrangeas to quickly grow back to its former size, so keep that in mind when it comes to your garden space and schedule.