How to Grow Ranunculi in Australia

Ranunculus (Ranunculus asiaticus), the Persian buttercup of the buttercup family Ranunculaceae, is grown for its layered, rose-like flowers in spring beds, pots and the vase. Each claw-shaped corm (botanically a cluster of tuberous roots) goes in during autumn and can send up flower after flower through spring. Most failures trace back to one thing: corms that rot from too much water before they ever shoot.

Three mistakes that matter

1. Soaking too long or planting into soggy soil. Corms left in water for more than about four hours, or planted into wet ground, often rot. Keep the soak short, as under Planting Corms, and plant into free-draining soil.
2. Planting the claws upwards. The claws are roots and the shoot grows from the top. An upside-down corm usually survives but wastes energy turning around, so it comes up late and weak. Set every corm claws down.
3. Planting too late in the year. Ranunculus flower best in cool weather, and days above about 25°C send them into summer dormancy. Late plantings run out of cool weeks before they flower. Plant in autumn so the flowers arrive before the heat.

When to plant

Plant once the soil has cooled after summer, usually from March in cool districts to May in warm ones. Anzac Day sits in the middle of that window across most of the south. Flowers usually follow three months or more after planting, later in cool districts, and keep coming for 8 to 12 weeks.

Corms that arrive while the soil is still warm can wait, dry, in a cool, dark cupboard. Pre-sprouted corms, described under Planting Corms, can flower about two weeks sooner, which helps where spring heat comes early.

Site, soil and setup

Ranunculus come from the eastern Mediterranean and south-west Asia, where winters are mild and wet and summers dry.

Where corms rotted last year, plant the next batch in a fresh, better-drained spot.

Weed status, state by state

Do not confuse the garden plant with the buttercups of paddocks and lawns. Creeping buttercup has glossy, golden yellow flowers with usually five broad petals, and spreads by runners through lawns, pastures and damp ground. Garden ranunculus has many-petalled flowers in a wide range of colours, grows from claw-shaped corms and does not run.

Container growing

Pots suit ranunculus well because the mix drains freely and a pot can be moved out of heavy rain. Bulbs have small root systems, so choose a squat, wide pot with drainage holes, at least 30 cm across (about 10 L). At 10 cm apart it holds about six corms. Fill it with premium potting mix and plant at the same depth as in the garden. The shorter lines, at 30 to 45 cm, suit pots best: the Trenton single colours, Bedazzle Blend and Dark Secrets.

• Watering. Water in once, then water when the top 2 cm of mix feels dry. Never leave the pot standing in a saucer of water.
• Feeding. Water in seaweed solution at 30 mL per 9 L every fortnight from the first shoots. From the first flowers, switch to liquid potash at the label rate every fortnight.
• Position. Full sun while in leaf. Move the pot under cover in long wet spells and once the leaves die down.

Planting Corms

Ranunculus start from dry, dormant corms, soaked briefly and planted claws down.

Pre-sprouting

Soak the corms in room-temperature water for 3 to 4 hours, until they plump up, and no longer. To pre-sprout, half-fill a seed tray with moist potting mix, lay the corms on it claws down and cover them. Keep the tray dark at 4 to 10°C for 10 to 14 days. Every few days, check that the mix is moist but not soggy, and remove rotting corms. They are ready when swollen to twice their size, with white rootlets.

What the store sells

Planting a bed of corms

1. Prepare the bed as under Site, soil and setup.
2. Soak the corms as above. Pre-sprout them only if you have a dark spot at 4 to 10°C. Skip it where hard frosts below about minus 3°C are likely, because sprouted corms are more easily killed by cold.
3. Set each corm claws down, 4 to 5 cm deep in cool districts and up to 8 cm deep in warm ones.
4. Space corms 10 to 15 cm apart.
5. Water in gently once, then water only if the soil dries out until shoots appear.
6. Mark the rows, so a spade does not find the corms before the leaves do.

After flowering: keep, lift or replace

Once flowering ends, the leaves feed the corm, so leave them until they turn yellow and brown. Corms need a dry summer rest. Many weaken after one or two seasons, so plenty of gardeners treat them as annuals or biennials. To keep them, lift the corms once the leaves have died down and let them dry. Store them in a paper bag somewhere dry, airy and cool, about 10 to 13°C.

Care by growth stage

Steady moisture once the leaves are up, and cool weather while the buds form, decide how long ranunculus keep flowering. Feed lightly at planting, then shift to potassium as the flowers open.

If growth stalls in poor soil, a light dose of all-purpose controlled release granular (NPK around 14-5-10) scratched in as the leaves appear can help. Where frosts fall below about minus 3°C, lay straw mulch over the bed, since a hard freeze can kill plants and rot the corms.

Companion planting

Other cool-season bulbs and low spring flowers share the same autumn planting and fill the gaps between stems.

Grows well with

• Anemones, planted at the same time and depth, which flower alongside in beds and pots.
• Dutch iris, whose blue and purple flowers set off orange and gold ranunculus.
• Daffodils, which go in during autumn and flower earlier.
• Violas and pansies, low cool-season edging that covers bare soil.

Keep apart

• Vegie beds, where a corm or leaf could be eaten by mistake.
• Damp, shaded corners, where fungal disease and rot take hold.

Harvesting Blooms

Cut stems when the buds show full colour and feel soft and squashy, like a marshmallow, but before they open fully.

• Cut in the cool of the morning.
• Use clean secateurs and cut the stem low, near its base.
• Stand the stems straight in a bucket of water.
• Keep picking, because regular cutting encourages more flowers.
• Snap off spent flowers on plants left in the garden.

Cut ranunculus usually last 7 to 10 days in a vase and keep opening after cutting. The flowers are sensitive to ethylene gas, so keep the vase away from ripening fruit. Place it where cats and dogs cannot drink the water or chew the stems. Use the stems on their own or with other spring flowers in mixed arrangements.

Common problems

No shoots after planting. Corms that are soft or smell sour when dug have rotted, usually from wet soil or a long soak. See Three mistakes for the fix.

Short stems and few flowers. Late planting, strong wind or a run of warm days while buds form can shorten stems. Plant earlier, in full sun out of strong wind.

Flowering stops early in spring. Hot spells end the season, as under Three mistakes. Midday shade and steady water can stretch it a little.

Corms do not come back. Summer rain or watering rots dormant corms left in the ground. See After flowering under Planting Corms for when to lift them.

Pests and diseases

Most trouble arrives in damp spells in late winter and spring, when soft new growth is at its peak.

Aphids (family Aphididae). Aphids cluster on shoot tips and buds and spread plant viruses as they feed. Hose them off or spray with insecticidal soap. Read more

Garden snail (Cornu aspersum). Snails and slugs chew young leaves and buds at night in Australian gardens. Hand-pick on damp evenings, or scatter an iron-based bait thinly by its label, never in heaps, where dogs cannot reach the pellets or packet. Read more

Powdery mildew (Erysiphe aquilegiae). Recorded on ranunculus in Victoria, it coats leaves with a white powder, mostly in autumn and in crowded, still air. Remove badly affected leaves, space plants well and water at soil level. Read more

Grey mould (Botrytis cinerea). It attacks ageing petals in cool weather with heavy dew, covering them in a thick grey mould. Pick off affected and spent flowers and bin them, and keep plants well spaced.

Tomato spotted wilt virus (Orthotospovirus tomatomaculae). Found throughout Australia and carried by thrips, it causes ring spots, mottling and distorted leaves. Infected plants cannot be cured: pull and bin them, never keep their corms, and keep weeds down nearby.

Prevention first

• Plant only firm corms, and throw out any that are soft or mouldy.
• Keep to the spacing under Planting Corms, so air moves between the plants.
• Check new growth on damp evenings for snails and aphids.
• Clear spent flowers and yellowed leaves from the bed.

Tips

1. Set a kitchen timer when the corms go into water, so the soak stops at four hours.
2. Plant a second batch three or four weeks after the first to stretch the cutting season.
3. If you cannot tell which way is up, plant the corm on its side and the shoot finds its own way.
4. Grow a short row just for cutting, so picking does not thin the garden display.

Due to quarantine restrictions and our shipping policy, we cannot send ranunculus corms to Western Australia or Tasmania.