For all species, spent flowers should be trimmed back to the uppermost pair of new leaf buds. This should be done in early spring after the last frosts. Great care should be taken to avoid damaging new green shoots. To prune in the autumn or winter may encourage winter die-back. The dead flowers look great in winter when covered with a dusting of frost. Dead flowers can also be a safe haven for beneficial insects throughout a cold winter. Any dead leaves remaining on the plant over winter can also be removed as part of the dead-heading exercise.
(The exception is H. arborescens which should be dead-headed and pruned in autumn).
* No pruning is better than improper pruning
* Most species do not require regular pruning
* To avoid winter die-back, prune after the risk of late frosts
H. macrophylla and H. macrophylla ssp. serrata flower on the previous year’s growth and the flowers come from the terminal buds. So, do not give the shrub a ‘haircut’ as all flowers for the coming season will be lost. Instead, remove old and weaker new stems at the base; also remove one-third of old, large stems at the base each year. This will promote the growth of strong new shoots from the base.
H. arborescens can be cut back hard in autumn as this species will flower on new growth. They should be hard pruned (all shoots, branches, twigs) to about 30cm from the ground every year. H. arborescens, and its cultivars, can have a tendency to flop as the flowers become too heavy. To minimise this, it is advisable to prune the shape of the shrub into a dome by reducing the outer branches to 10cm, the next inner branches to 20cm and the central branches to 30cm. Even so, some support may still be necessary for cultivars such as H. arborescens ‘Annabelle’.
H. paniculata can be hard pruned in spring as these species will flower on new growth. Pruning is usually only required to maintain shape or restrict size. Prune back leaving only the two lower buds at the base of each stem.
H. petiolaris and H. anomala ssp. quelpartensis, the deciduous climbing hydrangeas, require no pruning other than to keep them within the space available. Also, to keep them tight to their support structures (fence, wall) it may be necessary to trim back forward-growing branches. Dead-heading is advisable as it promotes new flowers. H. petiolaris will bloom on new wood.
H. quercifolia, H. aspera, H. involucrata, H. heteromalla and H. scandens do not require very much pruning. Just cut back dead wood to promote new growth and thin out weaker growths. H. heteromalla will bloom on new wood.
H. seemannii and H. integrifolia, the evergreen climbing hydrangeas, require no pruning other than to keep them within the desired space and to keep them close to the wall or fence.
~ ~ Know your plant names so that you can apply the correct pruning regimen ~ ~
Pruning Hydrangea macrophylla ‘Nachtigall’
This shrub was moved, in October, when it was almost fully grown at 2m. (which proves it can be done). Some of the branches were damaged in the process, so it is now in need of pruning (in April).
There are approximately 20 major stems, so prune one-third of them (7) by removing branches at the base. This will promote new, strong, vertical shoots from the crown.
So as not to confuse the diagram only four pruning positions are shown; another three would probably made towards the rear.