Hydrangeas are a popular shrub that is grown for its impressive blooms. Their foliage can also be attractive, particularly oakleaf hydrangeas. There is often a fair amount of confusion when it comes to pruning hydrangeas. This happens because different species of hydrangea are pruned at different times of the year.
There are five species of Hydrangea that are commonly found in cultivation. These can be dived into two groups for pruning purposes; those that bloom on new wood and those that bloom on old.
This pruning is outside of the normal maintenance pruning that you can do at any time. Maintenance pruning includes removing diseased and dead wood; make sure to cut back to new, healthy wood, as well as dead heading spent flowers.
Hydrangeas that bloom on old wood start to develop their flower buds for the following year in August and September. Therefore, if you are going to be doing any pruning to these plants, try to prune them as soon as possible after they are done blooming and by August 1st at the latest. By doing this, you will avoid removing any of the developing flower buds.
The Hydrangea species that flower on old wood are Hydrangea macrophylla, which are commonly called big leaf hydrangea, mophead, and lacecap. H. quercifolia, which are also called oakleaf hydrangeas. Finally H. anomala, also called climbing hydrangea, will also bloom on old wood.
There are some varieties of H. macrophylla, which are remontant. These cultivars will produce on both old and new wood. An example of this are the Endless Summer ® hydrangeas.
Hydrangeas that bloom on new wood produce their flower buds on the current season’s wood. These plants can be pruned from late winter to early spring. These plants can be, and commonly are drastically cut back in the fall. Repeatedly doing this can weaken the plant though. Hydrangea species that bloom on new wood are H. paniculata, which is commonly called panicle or PG hydrangea, and H. arborescens, commonly called smooth hydrangea.