There are three categories of hydrangea, hydrangea macrophylla, the hydrangeas paniculata and arborescens, and the hydrangea petiolaris.
Pruning hydrangea macrophylla
hydrangea macrophylla flowers on wood of the preceding year, so you must wait to prune so as not to cut off the new buds.
When? Pruning will be easiest at the start of the new foliage, when the first leaves start to appear.
Cleaning your hydrangea: remove all the dead flowers from the previous summer and cut above the last bud on each branch. This will avoid the cutting of eventual flowering buds. Also cut out any dead, damaged or weak wood which will not have flowers.
Allow the light to enter: Open out the centre and cut to ground level the oldest branches (the thickest ones) remove branches that cross or run parallel to each other.
A few tips: leave the dead flowers in place until the pruning of the following year, this will protect the stems from disease and cold. Prune your adult hydrangeas every year to ensure the foliage is regularly renewed. You will then have magnificent compact hydrangeas which will flower for years.
Pruning hydrangeas paniculata and arborescens
hydrangeas paniculata and arborescens flower on the wood of the same year, so we must stimulate the production of new wood.
When ? Pruning should be done at the end of the summer, when the flowers are dead. In regions that have vigorous winters, it is better to await the re-start of the foliage
Cleaning your hydrangea: Remove dead flowers and cut out any dead, damaged or weak wood.
Allow the light to enter: You can prune the shoots of the year very severly to a few eyes or buds of the main stems. While always avoiding pruning the old wood of more than 2 years as these will not produce new shoots. Nevertheless, opening out as necessary the heart of your hydrangea so as to give it more light.
A few tips: a hydrangea that is pruned short each year will stay compact with a strong density of flowers, if you want it more bushy, only remove the dead flowers.
Pruning hydrangea petiolaris
This climbing hydrangea has slow growth rate in the first few years, and so be content just to remove dead flowers and any dead or damaged wood.