Hydrangeas are the shrub that can always be relied upon to put on a good show in part to full shade positions in NZ gardens. In the past we were limited to the standard 'mop top' or 'lace cap' varieties, but we now have more varieties available in NZ, including Oakleaf, Panicle, Smooth and climbing options.
It is important to correctly identify what variety of hydrangea you are pruning. This will guide you on how and when to prune correctly, as different varieties bloom on different-aged wood. Get it wrong and you could miss out on blooms for that entire season.
First things first: when pruning, always start by removing any branches that are dead, damaged or diseased.
Bigleaf Hydrangeas
'Mop top' flowers ('Bridal Bouquet', 'Raspberry Crush' etc.) and serrata with 'lace cap' flowers 'Blue Deckle' and 'Libelle' are some of the cultivars widely available in NZ.
Flower buds form the previous growing season, at or near the ends of the branches, easily recognisable as 'two fat buds' on the stems in late winter. If you cut back beyond them, you will forfeit your blooms for the upcoming summer. In cooler NZ regions, leave the old flower heads on the bush to protect the fat buds from winter cold. Prune in spring, cutting the stems back to just above the 'two fat buds'.
If you need to bring the height of the bush down, prune in late summer well before next year's flower buds have formed on the stems. You may have to sacrifice some blooms to make the cuts.
If the bush is getting crowded, thin out some of the excess twiggy branches to let air and light in.
Oakleaf Hydrangeas
'Pee Wee' and 'Snowflake' are some of the cultivars available in NZ.
Grown for their stunning large red, oakleaf-shaped leaves as much as the white panicle flowers. Prune the same way as the bigleaf hydrangeas, back to 'two fat buds', unless you're more interested in the foliage. In that case, cut the stems back by one quarter in late spring to stimulate leafy growth.
Panicle Hydrangeas
'Limelight', 'Candlelight' and 'Bombshell' are some cultivars available in NZ.
These varieties bloom on new season's growth, so prune in late winter to early spring, after the last heavy frosts and before new growth starts shooting. The buds should be swelling so you can tell if any have died during winter and need removing. Cut back each stem by about one third, to just above a node. Trim out any weak, wispy growth to focus the plant's energy into the bigger branches for a stronger plant and better show of blooms.
Smooth Hydrangeas
Such as 'Annabelle'. These also flower on new season's growth, so follow the steps for pruning panicle hydrangeas above.
Climbing Hydrangeas
'Petiolaris' climbs by attaching itself onto a support structure or wall. Prune in early spring before growth begins. Cut back overly vigorous branches and shorten flowering stems that are growing outwards from the support structure. The vine flowers on new shoots, so light pruning to stimulate growth is beneficial for more blooms.
Pruning your hydrangeas will encourage blooms and improve the health of the plant by removing dead or diseased branches. It will enable you to control the overall shape and size of the plant, keeping it happy and healthy in your NZ garden.
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Written for Bugg by Kelly Jean Reyland from Garden Advice NZ (www.gardenadvice.co.nz)
