Few shrubs deliver as much flower for as little effort as a hydrangea. From November through to March the mophead varieties carry blooms the size of dinner plates, in colours ranging from deep rouge to slate blue to pure white, all on a plant that actively prefers the shady side of the house where most flowering shrubs sulk. That combination of shade tolerance and sheer flower volume is why hydrangeas have held their place in Australian gardens for over a century.
They are also more forgiving than their reputation suggests. Get three things right, namely morning sun rather than afternoon sun, consistently moist soil and a correct winter prune, and a hydrangea will reward you for decades. This guide covers all three, along with the famous party trick of changing flower colour with soil pH.
Quick facts
| Botanical name | Hydrangea macrophylla and related species |
|---|---|
| Type | Deciduous flowering shrub |
| Height | 1m to 2m tall and wide |
| Position | Morning sun, afternoon shade |
| Soil | Rich, moist, well drained |
| Flowers | Summer, November to March |
| Climate | Cool temperate to subtropical |
The science behind hydrangea colours
Hydrangeas possess an extraordinary capability to change their bloom colour according to soil pH, which is truly a gardener's delight. The hues range predominantly from deep blues to vibrant pinks, with occasional whites and purples across the spectrum. This colour-changing trait is primarily observed in Hydrangea macrophylla, commonly known as bigleaf hydrangeas.
Acidic soils, with a pH below 5.5, yield blue blossoms, whereas alkaline soils above pH 6.5 turn the flowers pink. Adjusting soil pH is therefore a genuinely satisfying experiment for anyone looking to paint their garden with living colour. White varieties such as White Knight stay white regardless, so plant them where you want certainty. Our guide to lowering soil pH explains how to shift the balance safely rather than in one heavy application.
Choosing a hydrangea
Classic mopheads for colour
For rich colour, start with Diamond Rouge Hydrangea, a compact grower around 1.2m whose blooms open and deepen to an intense rouge red. If your taste runs darker, Obsidian Storm Cloud Hydrangea brings moody, deeply saturated tones that look superb against a light-coloured wall or fence.
For white gardens
Magical Pearl Hydrangea opens creamy white and ages through soft green and blush tones, so the display keeps changing across the season. For sheer size of bloom, Annabelle Hydrangea is famous for enormous white flower heads, and because it flowers on new growth it can be pruned hard every winter without losing a single bloom. Our guide to white hydrangeas covers how to use them in a single-colour border.
For deep shade and mild winters
The Evergreen Hydrangea (Dichroa versicolor) is a close hydrangea relative that keeps its foliage year round and produces clusters of blue flowers followed by metallic blue berries. It handles deeper shade than the mopheads and suits warm coastal gardens where a bare deciduous shrub through winter is less welcome.
Planting hydrangeas
Position is the decision you cannot undo, so get it right first. The ideal spot receives gentle morning sun and is protected from hot afternoon sun and drying westerly winds. The east or south-east side of the house is usually perfect. In cool hill districts hydrangeas will take more sun; in Brisbane and further north, treat afternoon shade as non-negotiable.
Hydrangeas thrive in well-drained soils enriched with organic matter, so dig through a generous amount of compost or aged manure before planting. These are hungry, thirsty plants that repay soil preparation handsomely. Plant at the same depth as the pot, space plants 1m to 1.5m apart for a continuous border, and water in thoroughly. A layer of mulch 5cm to 7cm deep is close to essential, keeping the shallow roots cool and cutting summer watering dramatically. Planting in early spring or autumn allows the plant to establish a robust root system before the extremes of summer or winter. They pair naturally with camellias and other shade-lovers, as covered in our guide to shade gardening.
Watering and feeding
The name comes from the Greek for water vessel, and the plant lives up to it. Water deeply two to three times a week in summer, more during heatwaves. Hydrangeas prefer consistently moist soil but are susceptible to root rot if overwatered, so a balanced approach is ideal. A hydrangea flat on the canvas at 3pm will often stand back up by morning, but repeated wilting weakens it, so do not make a habit of testing this.
Feed in early spring and again in midsummer. Richgro Azalea and Camellia Fertiliser is formulated for exactly this group of acid-loving shrubs and keeps foliage deep green and blooms full sized. Providing a slow-release fertiliser in early spring supports healthy growth and abundant flowering.
Hydrangea care through the year
Once you learn their seasonal rhythm, hydrangeas are quite easy to care for. Here is how to look after them right through the year, whether you are growing them in the ground or in pots.
Summer (December to February)
What is happening: hydrangeas are in full bloom during summer. This is their time to shine.
- Water deeply two to three times per week in hot weather. Keep the soil moist, not soggy.
- Mulch around the base to lock in moisture and keep the roots cool.
- Deadhead spent flowers to tidy the plant and encourage more blooms.
- Protect from harsh sun if needed, especially in hotter parts of Australia.
Best spot: morning sun with afternoon shade is ideal for most varieties.
Autumn (March to May)
What is happening: blooms start fading, and the plant begins preparing for its dormant phase.
- Reduce watering as temperatures drop.
- Stop fertilising to avoid triggering new growth before winter.
- Do not prune yet, especially for varieties that flower on old wood.
- Leave dried flower heads on the plant for added winter texture if you like the look.
Autumn is the time to adjust your soil pH if you want to change bloom colour. For pink blooms, add lime. For blue blooms, add aluminium sulphate.
Winter (June to August)
What is happening: hydrangeas go dormant. Most will lose their leaves, which is entirely normal.
- Prune in late winter, just before new growth starts.
- Macrophylla types, meaning mophead and lacecap, need a light prune only.
- Paniculata and arborescens types can be pruned harder, as they bloom on new wood.
- Clean up fallen leaves and spent mulch to avoid pests overwintering.
- Check for rot or fungus in overly damp areas.
- Cover young plants if you are in a frost-prone area.
Not all hydrangeas need pruning every year. You can skip it if your plant is healthy and full.
Spring (September to November)
What is happening: hydrangeas wake up. Buds appear, leaves sprout and growth kicks off.
- Feed with a slow-release fertiliser designed for flowering plants.
- Resume regular watering as the days warm up.
- Watch for pests such as snails, slugs and aphids on new shoots.
- Reapply mulch to help retain moisture through summer.
If you had no flowers last year, check whether you pruned at the wrong time or whether your plant lacked sun or nutrients.
Pruning timing and technique
Prune in late winter. On mopheads, cut each stem that flowered back to a pair of plump buds about a third of the way down, and remove a few of the oldest canes at ground level to open the plant up. Do not shear the whole plant to stubs: macrophylla types flower on last season's wood, and a hard all-over cut costs you an entire summer of bloom. Annabelle is the exception and can be cut to 30cm annually without penalty.
This period of dormancy is crucial for pruning, particularly for varieties that bloom on old wood. Identifying and preserving healthy buds while removing dead or structurally weak branches fosters a vigorous flowering season through spring and summer.
Common problems
Scorched, crisped leaves: almost always too much afternoon sun or wind rather than disease. Move the plant in autumn or plant a taller screen to its west.
No flowers: the usual cause is pruning too hard or too late, removing the flowering wood. Prune in late winter only, and only back to fat buds. A late spring frost can also burn emerging buds in cold districts. Our guide to why your plant is not blooming works through the other possibilities.
Powdery mildew: a white film on leaves in humid, still corners. Improve airflow by thinning a few canes and water at the base rather than over the foliage.
Washed-out colour: blooms fading fast usually means too much sun or hungry soil. Shift your feeding earlier and check the mulch is holding moisture.
Over-pruning: one common mistake is over-pruning hydrangeas that flower on old wood. Excessive cutting back leads to reduced or absent blooms, so it is crucial to know which type you have before you start.
Ignoring soil conditions: neglecting soil pH diminishes the vibrancy of your hydrangea's colours. Regular soil testing and appropriate amendment maintains the shades you want. Avoid planting into heavy clay or waterlogged soil, which impedes root aeration and growth.
Frequently asked questions
How fast do hydrangeas grow?
Fast. A young plant typically reaches its full size of 1m to 2m within two to three seasons, flowering from its first summer.
Do hydrangeas grow well in pots?
Yes, they are excellent in pots of 40cm or wider with a premium potting mix. Potted plants dry out faster, so expect to water daily in summer.
Are hydrangeas frost tolerant?
Established plants handle frost well because they are dormant and leafless in winter. Late spring frosts can burn new shoots, so avoid frost hollows in cold districts.
Why are my hydrangea flowers green?
Many varieties naturally age to green late in the season. If blooms open green and stay small, the plant usually needs more light or a feed in early spring.
How do I get blue rather than pink flowers?
Lower the soil pH below 5.5 by applying aluminium sulphate in winter and spring, and avoid lime anywhere near the plant. In pots this is much easier to control than in open ground, particularly on naturally alkaline soils.
Ready to plant?
Hydrangeas offer an unusual combination: enormous flowers, genuine shade tolerance and a colour that responds to how you treat the soil. Understand their seasonal rhythm and they are among the most rewarding shrubs you can grow.
Browse our full range of flowering shrubs and evergreen shrubs to build out a shade border, or explore our shrubs collection for companions. Camellias make natural partners, and our guide to camellia bushes covers how to combine the two.
