How to Grow Carnations in Australia

Carnation (Dianthus caryophyllus) is a clove-scented perennial in the pink family (Caryophyllaceae), grown for its ruffled double flowers in borders and in the vase. The two common seed strains behave differently: Chabaud often flowers in its first summer, and the hardier Grenadin tends to peak a year later. Carnations cope well with dry Australian heat, and the usual mistake is too much water, which rots the crown.

Three mistakes that matter

1. Keeping the soil wet. Carnations dislike wet feet, and soggy soil or mulch heaped against the stems rots the crown and roots. Plant in free-draining soil, water at the base only once the surface dries, and see waterlogged soil for heavy ground.
2. Sowing too late for flowers that year. Plants take roughly 19 to 29 weeks from sowing to flower, so a late sowing may give only a few blooms before the cold. Sow early in your zone's window, and expect Grenadin to do its best in the second year.
3. Crowding plants in a shady, still corner. Carnations need full sun, and crowded, damp foliage invites rust and grey mould (Botrytis). Give them 6 hours of sun or more, keep to the spacing under Sowing Seeds, and water the soil rather than the leaves.

When to plant

Seed germinates best when the mix holds 18 to 24°C. Most gardens therefore have two windows: autumn while the soil is still warm, and spring once it warms again. Autumn sowings usually flower from late spring, and spring sowings from late summer. One sowing can flower for several seasons.

At the late edge of the autumn window, keep seedlings in their cells under cover until spring rather than planting them into cold soil.

Site, soil and setup

Carnations want sun on their leaves, air around their stems and water that drains away fast.

For more on testing and adjusting your ground, see soil pH.

Container growing

Carnations grow well in pots, which also sidestep heavy clay. Use a pot of at least 10 L, no less than 20 cm across and 20 cm deep, filled with free-draining potting mix. Neither strain the store sells is a dwarf. Of the two, 'Grenadin White Double' suits a pot best, with sturdy stems about 60 cm tall, while 'Chabaud Giants Mixed' needs a short stake.

• Watering: water at the base when the top of the mix feels dry, until it runs from the drainage holes; see watering pots in summer.
• Feeding: fish and seaweed blend at 25 mL per 9 L every fortnight, from spring growth to the end of flowering.
• Position: full sun, with the pot raised on feet so it never stands in water.
• Winter: water sparingly while growth is slow, and keep the saucer empty.

Sowing Seeds

Raise carnations in cells and transplant them, or sow direct into a fine bed in spring and autumn. The two strains differ in ways that change the timing and the staking.

Starting under cover

• Fill cells or a tray with fresh seed raising mix and water it well before sowing.
• Sow two or three seeds per cell, 6 mm deep, and firm the mix gently over them.
• Hold the mix at the temperature under When to plant; a seedling heat mat helps in cool weather. Seedlings usually appear in 1 to 2 weeks.
• Keep the mix moist but never soggy, watering from below or with a fine mist.
• Move trays into full light as soon as seedlings show, so they stay short and sturdy.
• Thin each cell to the strongest seedling by snipping the others at soil level.

Sowing direct

Rake the bed to a fine surface and sow small groups of seed 6 mm deep, 30 to 40 cm apart. Keep the surface moist until seedlings show, then thin each group to the strongest. Mark each spot, because the young leaves are narrow and grassy and easy to weed out by mistake.

Transplanting

Plant out when seedlings are 5 to 10 cm tall. Harden them off first (a week or so of gradually longer spells outdoors that toughens soft growth), as in hardening off seedlings. Set each plant 30 to 40 cm apart at the depth it grew, never deeper. Water in with seaweed solution at 30 mL per 9 L.

Care by growth stage

Drainage and sun decide how carnations grow, far more than feeding does. Once established they cope with dry spells, so water deeply and let the surface dry out between waterings.

Chabaud stems are long and wiry, and they tend to topple under their flowers. At planting, push in a few stakes or stretch netting about 30 cm above the soil, and let the stems grow up through it. If growth stalls in poor soil, a light dose of all-purpose controlled release granular (NPK around 14-5-10) scratched in as growth starts can help.

Disbudding and Deadheading

Disbudding sets the size of each bloom, and deadheading sets how long a plant keeps flowering. Both are fingertip jobs, done every few days while plants are in flower.

• Pinch out the growing tip of each young plant once it is about 20 cm tall, so it branches and carries more stems.
• For one large flower per stem, rub out the side buds while they are the size of a pea and keep the top bud.
• For a spray of smaller flowers, snap out the top bud instead, so the side buds open together.
• Snap off each faded flower down to the next bud or pair of leaves.
• Once a stem has finished, cut it back to a leafy shoot near the base.
• At the end of summer or in early autumn, cut tired plants back by half to bring on fresh growth.

Companion planting

Carnations belong at the front of a sunny border, in a raised bed or in a cutting row, where nothing shades or crowds them.

Grows well with

• Lavender, which wants the same full sun, free drainage and little water once established.
• Everlasting daisies, which share the taste for sun and dry summers and suit the same cutting bed.
• Violas along the front edge, low enough never to shade the carnation crowns.

Keep apart

• Mint and other runners, which smother the crowns and compete for water.
• Sweet William (Dianthus barbatus) and other dianthus, which share rust and wilt, so grow them in separate beds.
• Thirsty vegetables on daily watering, whose constantly wet soil rots carnation crowns.

Harvesting Blooms

Cut a single-flowered stem when its bloom is about half open, and a spray when one or two of its flowers have opened.

• Pick early in the morning, when the stems are full of water.
• Carry a bucket of water and stand each stem in it straight after cutting.
• Cut with sharp, clean secateurs just above a pair of leaves.
• Strip any leaves that would sit below the water in the vase.
• Pick every few days while plants flower, because removing blooms keeps new ones coming.

Stems can last up to 2 weeks in a vase with flower food. Change the water when it clouds. Keep the vase away from ripening fruit, which gives off ethylene (a gas that speeds ageing) and makes carnation petals wilt early. If stems will not be displayed straight away, keep them somewhere cool, between about 4 and 15°C.

The petals are edible and taste mildly of cloves, so they suit salads, cakes and cold drinks. Pull them from the flower and leave the bitter centre behind.

Common problems

Seeds did not come up. Cold or drying mix is the usual cause, so hold it at the temperature under When to plant and keep it evenly moist. Read more

Tall, floppy seedlings. Too little light stretches them, so move trays into full sun or bright light as soon as seedlings appear. Read more

No flowers in the first season. A late sowing, or Grenadin's habit of flowering best from its second year, is the usual reason; see Three mistakes that matter.

Older plants flower less. Many carnations are short-lived perennials, so raise replacements from seed, or root cuttings as under Tips, while the old plants still flower.

Pests and diseases

Most carnation troubles in Australian gardens are sap-suckers in warm, dry weather and fungal diseases in wet or crowded beds.

Aphids (Aphididae). These small green, black or brown insects cluster on shoot tips and buds and distort the growth. Hose them off, and for repeat outbreaks spray horticultural oil or soapy water, never in hot weather. Read more

Thrips (Thysanoptera). These tiny insects, usually 1 to 2 mm long, leave silvery-brown speckling and streaks on leaves. Hang yellow sticky traps and spray insecticidal soap every week for four to six weeks, sparing ladybirds and lacewings. Read more

Two-spotted mite (Tetranychus urticae). These tiny mites feed under the leaves, leaving a pale, stippled look and fine webbing, and they are worst in hot, dry weather. Mist or hose the undersides of the leaves, and spray insecticidal soap or wettable sulphur for bad outbreaks. Read more

Slugs and snails (Gastropoda). They chew seedlings and soft young shoots overnight. Search under leaves and around rocks by day, and set shallow beer traps dug slightly into the soil. Read more

Carnation rust (Uromyces dianthi). Chocolate-brown pustules form on leaves and stems, and badly infected plants are stunted. Pick off infected leaves, give plants room for air to move, and clear plant debris in autumn.

Fusarium wilt (Fusarium oxysporum f. sp. dianthi). Plants turn dull green, wilt on one side and turn straw-coloured, often with brown streaks inside a cut stem. It cannot be cured, so bin the plant with its roots and grow carnations elsewhere.

Prevention first

• Plant in full sun and free-draining soil, and water the soil rather than the leaves.
• Keep to the spacing under Sowing Seeds, so leaves dry quickly after rain.
• Check shoot tips and the undersides of leaves every week in warm, dry weather.
• Clear faded flowers and fallen leaves, as in garden hygiene.

Tips

1. Keep a favourite plant going by rooting a few non-flowering side shoots as cuttings; see taking cuttings.
2. Grow a short row purely for picking, so the border keeps its display while the vase stays full.
3. Plant beside a path, a gate or an open window, where the clove scent carries on warm evenings.