How to Grow Dianthus in Australia

Dianthus (Dianthus chinensis), also called Chinese pink or Indian pink, is a low, clumping flower in the carnation family (Caryophyllaceae). It is grown for its fringed, often clove-scented flowers in white, pink, red and purple, many with a darker central eye. It is a hardy perennial usually grown as an annual, and one sowing gives months of colour in beds, pots and posies. The usual mistake is treating it like a thirsty bedding plant, because wet soil rots the crown long before heat or cold does any harm. Sweet William (Dianthus barbatus) and carnations (Dianthus caryophyllus) are close relatives, not covered here.

Three mistakes that matter

1. Wet feet. Heavy soil, daily watering and mulch piled against the stems rot the crown, and the plant yellows and collapses from the base. Plant in free-draining soil, water only when the top dries and keep mulch clear of the crown.
2. Sowing into the heat. Chinese pinks dislike hot, humid summers, and spring sowings in warm zones often burn out before they flower well. Sow in late summer and autumn in warm zones so plants flower through the cooler months.
3. Leaving spent flowers on. Faded heads left on the plant slow new flowering and turn a neat mound ragged. Snip them off each week and shear the whole plant lightly when a flush ends, as under Deadheading.

When to plant

Seedlings emerge in 10 to 15 days when the seed raising mix sits at 18 to 24°C. Sow when days are mild rather than hot. In most zones that means late summer and autumn, and plants flower from late winter into spring. In cool gardens, sow in spring for flowers from late spring into autumn. Plants take about 20 weeks from sowing to first flower.

In warm zones, finish autumn sowings by about Anzac Day so seedlings settle before the short days slow them. Sowings at the hot end of a window do better started under cover in bright shade.

Site, soil and setup

Sun, air and drainage decide how long a planting lasts. Dianthus copes with coastal gardens, dry spells and frost, but not with a bed that stays wet.

After an outbreak of rust or crown rot, replant dianthus in a different bed. For more on reading and adjusting your soil, see soil pH and waterlogged soil.

Container growing

Pots suit dianthus well, because a pot drains freely and dries out evenly. Use a pot at least 15 cm across, about 2 L, for one plant. A bowl 30 cm across, about 8 L, holds three to five. Fill it with a free-draining potting mix. 'Baby Doll Mix' and 'Merry Go Round' grow to about 20 cm and suit pots and hanging baskets.

• Watering: water when the top 2 cm of mix is dry, then let the pot drain; see watering pots in summer.
• Feeding: fish and seaweed blend at 25 mL per 9 L every fortnight while plants are budding and flowering.
• Position: full sun, with afternoon shade on hot summer days.
• Drainage: stand pots on feet and never leave them in a saucer of water.

Sowing Seeds

Raise dianthus in trays or cells and plant out after about six weeks, or sow straight into a prepared bed.

Starting under cover

• Fill trays or cells with fresh seed raising mix and water it before sowing.
• Sow seed 3 mm deep, one or two per cell, and cover lightly with fine mix or vermiculite.
• Keep the mix moist but never soggy, at the temperature under When to plant.
• Give seedlings bright light as soon as they emerge, so they stay short and sturdy.
• Thin each cell to the strongest seedling by snipping the others at soil level.

Sowing direct

Rake the soil to a fine surface, sow seed 3 mm deep in small groups at the spacing in the table below, and cover lightly. Keep the surface just moist with a fine spray until seedlings show. Thin each group to the strongest seedling.

Transplanting

Plant out when seedlings have about four pairs of leaves, usually 5 to 6 weeks from sowing. Harden them off first (a week or so of gradually longer spells outdoors that toughens soft growth), as in hardening off seedlings. Set each crown level with the soil surface, never deeper, and water in with seaweed solution at 30 mL per 9 L. Space plants by the mix you grow.

Care by growth stage

Drainage and a light hand with feed decide how long dianthus keeps flowering. Seedlings are sensitive to strong fertiliser, so every feed stays mild.

Keep mulch thin and clear of the crown, where it traps moisture and invites rot. If growth stalls in poor soil, a light dose of all-purpose controlled release granular (NPK around 14-5-10) scratched in at planting can help.

Deadheading

Dianthus flowers in flushes, and regular deadheading plus a light shear between flushes brings the next round of buds.

• Snip each faded flower stem back into the mound of foliage, where new shoots are forming.
• When a flush finishes and flowering slows, shear the whole plant lightly to promote more flowers.
• Water and feed after shearing, as in the flowering row of the care table.
• In autumn, trim faded blooms and any scruffy leaves to tidy the plant for the cool months.
• Pull out plants that turn woody and bare in the centre, and replace them from seed.

Companion planting

Dianthus belongs at the sunny front of a bed, in a rockery or along a path edge, beside plants that like the same dry feet.

Grows well with

• Lavender, which wants the same full sun, free drainage and light watering.
• Thyme, a low, sun-loving edging plant that shares dry, lean soil.
• Aubretia, which trails over rockery stones beside dianthus in the same sunny, free-draining spot.

Keep apart

• Mint and other spreading runners, which smother the low mounds and need moist soil.
• Sprinkler-watered beds, where wet leaves every day encourage rust.
• Large sprawling crops such as pumpkin, which shade and crowd small plants.

Harvesting Blooms

Cut stems for the vase when the flowers are just opening, because tight buds give less scent.

• Pick early in the morning, when stems are full of water.
• Carry a bucket of water and stand each stem in it straight after cutting.
• Cut just above a pair of leaves, so side shoots carry the next flowers.
• Strip any leaves that would sit below the water line.
• Grow 'Gaiety Double Mix' for the longest stems, and 'Merry Go Round' for small posies.

Cut dianthus often lasts 7 to 21 days in a vase. Change the water every 3 days, and keep cut stems somewhere cool, between about 4 and 15°C, if they will not be displayed straight away.

Short stems suit small posies and jam jars on a windowsill, where the scent carries across a room.

Common problems

Seeds did not come up. Seed sown too deep, mix kept too wet or too cold, or old seed are the usual causes. Read more

Tall, floppy seedlings. Too little light or too much warmth after emergence stretches the stems, so move trays into bright light straight away. Read more

Plants yellow and collapse from the base. Wet soil or mulch against the stems has rotted the crown; see Three mistakes that matter.

Flowering stops in summer. Hot, humid weather can burn plants out; shear them back, give afternoon shade, and sow again in late summer.

Bare, woody centre. Older plants sprawl and go woody at the base after a few years, and poor drainage makes the centre die out sooner.

Pests and diseases

Most dianthus troubles are sap-suckers on soft growth or fungi that follow wet leaves and wet soil.

Aphids (Aphididae). These soft green, black or brown insects, about 2.5 mm long, cluster on shoot tips and buds and distort the leaves. Hose them off or prune the worst tips, and for repeat outbreaks spray soapy water or horticultural oil, 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 and petals. Hang yellow sticky traps and spray insecticidal soap weekly for four to six weeks, sparing ladybirds and lacewings. Read more

Two-spotted mite (Tetranychus urticae). Mites under 0.5 mm long leave yellow mottled or stippled patches, mostly on leaf undersides, and multiply fast in hot, dry weather. Predatory mites and small black ladybirds usually keep them down when broad sprays are avoided. Read more

Slugs and snails (Gastropoda). They chew young seedlings and soft leaves, most of all in shady, damp beds. Check under leaves and around rocks where they shelter by day, and set shallow beer traps dug slightly into the soil. Read more

Carnation rust (Uromyces dianthi). Chocolate or cinnamon-brown powdery pustules with a yellow margin break out on leaves and stems, and badly hit plants stop flowering. Pick off affected leaves, water at the base and space plants for air.

Crown rot (soil-borne fungi). Plants in wet, poorly drained soil wilt, yellow and rot at the soil line. Lift and bin affected plants with their roots, then fix drainage before replanting.

Prevention first

• Plant in free-draining soil and water at the base in the morning, so leaves dry quickly.
• Space plants so air moves freely between them.
• Check leaf undersides for mites and thrips during hot, dry spells.
• Keep broad sprays off the bed so predators can work, and clear spent stems as in garden hygiene.

Tips

1. Pinch out the growing tip of each young plant once, soon after planting out, for bushier plants with more flowering stems.
2. Keep a favourite colour by taking cuttings about 6 cm long from non-flowering shoots; they usually root in four to six weeks.
3. Dianthus suits coastal gardens, where it makes a tidy, scented edging along a sunny path.
4. Bees and butterflies visit the flowers, so a row near the vegie patch can bring in pollinators.