How to grow Dahlia in Australia
Dahlias grow from tubers planted in spring and flower from about Christmas into autumn, in every size from small pompons to giant dinner plates. They want sun, rich soil that drains well, a stake from the day they are planted and regular picking. The tubers multiply each year, so one plant soon gives you more to share.
📖 Our full guide: How to Grow Dahlia in Australia
At a glance
When to sow by region
| Region | When to sow | Regional note |
|---|---|---|
| South East Queensland | August to November | |
| Northern Rivers NSW | August to November | |
| Sydney & Coastal NSW | September to November | Plant tubers Sep to Nov once the soil has warmed; they rot in cold wet ground. |
| Melbourne & Victoria | September to November | Plant tubers Sep to Nov once frosts finish in mid September. Lift or mulch heavily in cold inland gardens once frost blackens the tops. |
| Adelaide & SA | September to November | Plant tubers Sep to Nov after frost. Mulch and water deeply through heatwaves; flowers peak in autumn. |
| Perth & WA | August to November | |
| Tasmania | October and November | Plant tubers Oct to Nov after frost. Lift or mulch heavily in cold inland gardens. |
| Canberra & ACT | November | Plant tubers in November after the last frost. Lift or mulch heavily once frost blackens the tops in April. |
| North Queensland | April to August | Grow as a dry season annual. Plant Apr to Aug, enjoy the flowers, then lift the tubers before the wet or they rot. |
| Darwin & Top End | April to July | Grow as a dry season annual. Plant Apr to Jul, then lift the tubers before the build up or they rot in the wet. |
Where to plant
Plant dahlias in full sun in moist, humus-rich soil that drains well. Dig in compost or aged animal manure before planting. The tubers rot in cold, wet ground, so a well-drained bed matters most in winter. Choose a spot sheltered from strong wind, or be ready to stake well, as tall dahlias fall over in a gust.
Give plants enough room for air to move between them, which cuts down powdery mildew.
- South East Queensland and the Northern Rivers: plant from August to November.
- Sydney, Melbourne and Adelaide: plant from September to November once the soil has warmed and frosts are over. In Adelaide, mulch and water deeply through heatwaves; the best flowers come in autumn.
- Hobart: plant in October or November after frost.
- Canberra: plant in November after the last frost, and lift or mulch heavily once frost blackens the tops in April.
- North Queensland and Darwin: grow dahlias as a dry season annual. Plant from April to August (April to July around Darwin), enjoy the flowers, and lift the tubers before the wet, when they rot.
Choosing a variety
Dahlias are grouped by flower form. Decorative types have full, double flowers; cactus types have narrow, rolled petals; pompons are small, tight balls; and anemone types have a cushion of short petals in the centre. Gardening Australia notes that the small pompon types cope with rain better than the tall ones.
Single and open-centred dahlias give bees easy access to pollen, while full doubles are of little use to pollinators. For cut flowers, choose long-stemmed varieties and plant a few more than you think you need.
How to plant
- Dig compost or aged manure into a sunny, well-drained bed.
- Push in a strong stake before you plant, so you do not spear the tuber later.
- Lay each tuber flat beside its stake with the eye, the bud at the old stem end, facing up. Cover so the top of the tuber sits at or just below the soil surface.
- Space most varieties about 60 cm apart.
- Do not water until shoots are about 15 cm tall unless the soil is very dry, as tubers can rot before they start to grow.
- When the stems reach about 40 cm, pinch out the growing tip just above a pair of leaves to make a bushier plant with more flowers.
Watering and feeding
Once plants are growing strongly, dahlias are thirsty. Water deeply in dry and hot weather, and mulch to keep the soil moist. Plants that dry out are more prone to powdery mildew. Water the soil rather than the leaves.
Feed with a potassium-rich fertiliser, such as a liquid tomato feed, every couple of weeks once buds form, especially for plants in pots. Too much nitrogen gives lots of leaf and fewer flowers.
Pruning and care through the year
- Tie stems to the stake as they grow; tall varieties up to 1.8 m need several ties or a cage of four stakes and twine.
- Deadhead weekly, cutting back to a leaf joint lower down the stem, to keep new flowers coming.
- In late autumn, once frost or cold browns the plant, cut it back to near ground level.
- Where the soil drains well and does not freeze, tubers can stay in the ground over winter under a thick mulch. In heavy, wet soil or very cold areas, lift them.
Cutting flowers
Cut flowers when they are fully open, as dahlia buds open very little after cutting. Pick in the cool of the morning, take a long stem, and put it straight into water. Cut dahlias last about a week in a vase. The more you cut, the more flowers the plant makes.
Growing in pots
Shorter and pompon dahlias grow well in a pot at least 40 cm wide with good drainage, filled with a quality potting mix. Potted dahlias need regular watering all season and a potassium-rich liquid feed every couple of weeks once buds appear. Give tall varieties a stake in the pot from the start.
Lifting, storing and dividing tubers
- Lift tubers in late autumn once the leaves and flowers have browned. Lever around the clump with a garden fork, lift it, cut off the old stems and shake off the soil.
- Turn the clump upside down for a few weeks to let water drain out of the hollow stems, so they do not rot.
- Store in a box of slightly damp, not wet, sawdust or mulch, covered so the tubers do not dry out, in a dark, cool, dry place away from rats and mice.
- In spring, divide the clump when shoots are about 2.5 cm long. Cut it into pieces that each have a tuber and at least one eye, then replant.
Companion planting
Dahlias sit happily in a mixed flower bed or at the end of a vegetable bed, where they bring in bees and other insects. Other sun-loving summer flowers make good neighbours.
Good companions
- Marigold A summer annual that likes the same sunny spot and draws in beneficial insects.
- Zinnia Shares the same warm, sunny conditions and flowers at the same time, which makes a long-lasting cutting bed.
- Cosmos An easy summer flower that suits the same bed and brings in pollinators and beneficial insects.
Pests and diseases
The worst damage is done at night by chewing pests, and by mildew late in the season.
Pests to watch for
- Earwigs Ragged holes in petals and young leaves, with no slime trail. They hide in the flowers and leaves by day.
- Slugs Young shoots eaten off at ground level in spring, with slime trails. Protect new shoots as they emerge.
- Snails Holes in leaves and shoots and silvery slime trails, mostly after rain or watering.
- Aphids Clusters of small soft insects on shoot tips and buds. They also spread virus.
Diseases to watch for
- Powdery mildew White powdery patches on the leaves in late summer and autumn, worse on crowded or dry plants. Space plants and water well.
- Botrytis Grey, fuzzy mould on flowers and buds in cool, wet weather, and stored tubers that rot. Remove spent flowers and store tubers dry.
- Dahlia mosaic virus Pale, mottled or yellow-banded leaves and stunted plants. There is no cure, so dig out and bin affected plants and do not divide them.
Common questions
When should I plant dahlia tubers?
In spring once the soil has warmed and frosts are over: August to November in south east Queensland, September to November in Sydney, Melbourne and Adelaide, and November in Canberra. In the tropics, plant in the dry season from April.
Do I need to dig up dahlias in winter?
Only if your soil stays wet or freezes in winter. In well-drained soil, cut the plants back in late autumn, mulch thickly and leave the tubers in the ground. In heavy soil, cold inland areas and the tropics before the wet, lift and store them.
Why are my dahlia tubers rotting?
Usually from being watered before they sprout, or from cold, wet soil. Plant into well-drained soil, do not water until shoots are about 15 cm tall unless the soil is very dry, and store lifted tubers in barely damp sawdust in a dry place.
How long do dahlias take to flower?
About eight weeks from planting. Tubers planted in October or November usually start flowering around Christmas and continue into autumn.
What is eating my dahlia flowers?
Ragged holes in the petals are usually earwigs, which feed at night and hide in the flowers by day. Slime trails point to slugs and snails. Check plants after dark with a torch to see what is there.
Should I pinch out dahlias?
Yes. When the stems are about 40 cm tall, pinch out the tip just above a pair of leaves. The plant branches, grows bushier and gives more flowers.
How do I divide dahlia tubers?
In spring, when the eyes start to shoot, cut the clump into pieces that each have a tuber and at least one shoot or eye. A tuber without an eye will not grow.
Sources we checked: Gardening Australia: Dahlias; Gardening Australia: Plant profile, dahlias; Gardening Australia: Storing dahlias; Gardening Australia: Digging up dahlias; RHS: Dahlia growing guide.