Hydrangeas

Choosing by colour behaviour, not just colour

With every variety here finishing at a similar size, the real differences are in the flowers. The classic mopheads (Hydrangea macrophylla) respond to soil chemistry: 'Obsidian Storm Cloud' carries its blooms blue to purple in acid soil and pink in alkaline, over unusually dark stems and foliage. If you want a colour that never argues with your soil, 'White Knight' stays pure white regardless of pH, and 'Magical Pearl' opens white then ages to lime green and pink. 'Annabelle' is the cool climate favourite, a fast growing 1.4m shrub with big white heads, while 'Diamond Rouge' opens creamy white and deepens to red as autumn approaches. The odd one out is the Evergreen Hydrangea (Dichroa versicolor), which holds its foliage year round and suits gardens that never freeze.

Where hydrangeas grow well

The rule that matters is morning sun, afternoon shade. In cool temperate gardens around Melbourne, Hobart and the ranges, all the deciduous varieties are frost hardy and can take more sun. In Sydney, Perth and the subtropics, afternoon shade is non negotiable, and the mopheads plus the evergreen type handle Brisbane humidity well. In the tropics, only the evergreen form is a sensible choice. South facing beds, the shaded side of a fence and sheltered courtyards are ideal spots, covered in more depth in our guide to shade gardening in Australia.

Planting and spacing

Plant into soil enriched with compost, in a spot with shelter from hot afternoon wind. Space 'Magical Pearl' at 80cm, 'White Knight', 'Annabelle' and the evergreen form at 1m, and 'Diamond Rouge' at 1.2m for a massed border. Water deeply two or three times a week through the first summer; the name comes from the Greek for water, and a dry establishment year is the most common way to lose one. Mulch 75mm deep to keep the roots cool. In pots, use a 40cm to 50cm container and expect to water daily in summer heat.

Pruning and colour management

Prune in late winter. On the mopheads, cut back to a pair of fat buds below each spent head and remove the oldest canes at the base, because they flower on older wood. 'Annabelle' and 'Diamond Rouge' flower on new season growth, so they can be cut back harder to 30cm to 50cm and still bloom. To push a pH sensitive variety blue, feed with aluminium sulphate in autumn and winter; garden lime nudges it pink. It is a slow shift over a season, not a switch.

Common questions

Why are my blue flowers turning pink?

Your soil is more alkaline than the grower's mix. Apply aluminium sulphate through autumn and winter and mulch with composted leaves, and the blooms will drift back to blue over the next season or two.

Can I grow them in Queensland?

Yes. The mopheads and the evergreen form both cope with subtropical humidity, provided they get afternoon shade and steady water. North of the subtropics, choose the evergreen type.

Why is my plant wilting every afternoon?

Afternoon sun and big soft leaves. If it recovers by evening it is coping, but move it or add shade if the wilting starts before midday. Deep watering beats frequent light sprinkles.

Are hydrangeas safe for pets?

No. Leaves, buds and flowers are toxic to cats and dogs, so plant them away from animals that chew or pick from our pet safe plant range instead.