How to Grow Scabiosa in Australia

Scabiosa, or pincushion flower, covers two annuals of the honeysuckle family, Caprifoliaceae. Sweet scabious (Scabiosa atropurpurea) is grown for long-stemmed cut flowers, and starflower (Scabiosa stellata) for its papery seed heads. Both come from the Mediterranean, so they suit the mild months of Australian gardens and bring bees and butterflies to the bed. The usual mistake is sowing into summer heat and humidity, which the plants dislike.

Three mistakes that matter

1. Sowing into the heat. Sweet scabious dislikes heat and humidity, so late spring sowings in warm zones often flower briefly and collapse. Sow in autumn in the tropics and subtropics, and keep to your zone's window under When to plant.
2. Heavy, wet soil. Roots rot where water lies, and plants in sodden clay often die before they flower. Choose free-draining ground or a raised bed, following Site, soil and setup.
3. Cutting Drumstick too late. Once the star-shaped centres of the seed heads turn fully black and start to drop out, the heads shatter. Cut them at the stage described in Harvesting Blooms.

When to plant

Seed comes up in about 10 to 12 days in soil of 18 to 21°C, and plants flower best in mild weather. Autumn is the main sowing time in every zone, with Anzac Day inside the southern autumn window. Temperate, Mediterranean and cool gardens can sow again from late winter into spring.

Early in a window, while days are still hot, raise seedlings in trays in light shade and plant them out as the weather cools. Where frost lingers, start spring sowings in trays under cover and plant them out after the last frost.

Site, soil and setup

Give scabiosa full sun, at least 6 hours a day, and free-draining soil with some organic matter. It prefers neutral to alkaline soil, from about pH 6.0 upwards. In hot inland and northern gardens, light shade from the midday sun can help.

Damping off fungi carry over in the old roots and leaves of earlier crops. Choose a fresh spot if a sowing failed that way the year before.

Container growing

All four varieties grow in pots, and a heavy pot in a spot sheltered from wind keeps the tall stems upright. Allow 10 L of potting mix or more per plant; a 30 cm pot holds about 13.5 L, and it needs drainage holes. Legionella bacteria can live in bagged mix. Wet the mix before opening it up, wear a mask and gloves, and scrub your hands when done.

• Watering: once the mix feels dry below the surface, soak it until water drips from the base.
• Feeding: potted plants run short of food sooner. Once buds show, water on fish and seaweed blend at 25 mL per 9 L each fortnight.
• Position: the sunniest spot you have, out of strong gusts.

Sowing Seeds

Scabiosa can go straight into the bed or start in trays 4 to 6 weeks ahead of planting out. Due to quarantine restrictions and our shipping policy, we cannot send Drumstick seed to Western Australia.

Sowing direct

• Rake a fine, level seedbed and cover the seed lightly, no deeper than 5 mm, because light helps it germinate.
• Water with a fine rose, then keep the surface damp but not soggy until seedlings show.
• Expect shoots in about 10 to 12 days.
• Thin to 25 to 40 cm apart once the first true leaves open.

Starting in trays

• Sow into punnets of fresh seed raising mix, the seed just covered.
• Pot each seedling on into its own cell once its first true leaves open.
• Harden off the seedlings (give them a little more time outdoors each day over about a week, until they cope with full sun and wind).
• Plant out at 5 to 10 cm tall, settling each one in with half-strength seaweed solution, 15 mL per 9 L.

The three sweet scabious varieties share one method from sowing to picking. Drumstick is grown for its seed heads rather than its small flowers, so it is cut at a different stage.

Care by growth stage

Scabiosa dislikes being overfed and lives mostly on the compost in its bed. Steady water at the roots, dry leaves and regular cutting keep the stems coming.

On thin, hungry ground where plants sit still, scratch in controlled release all-purpose granules (NPK around 14-5-10) at the label rate.

Deadheading

Every head allowed to ripen seed draws on the plant, so sweet scabious slows its flowering unless spent heads come off.

• Every few days: snip each browning sweet scabious head back to the next pair of leaves.
• Cutting for the vase: counts as deadheading, so pick often.
• Drumstick: leave the faded flowers, because the seed heads that follow are the crop.
• Near bushland or grassland: remove every head before seed drops, as the tips below explain.
• End of flowering: pull out spent plants and compost them.

Companion planting

Scabiosa sits well in a cutting bed with flowers that share its sun, soil and sowing months.

Grows well with

• Cornflowers: sown in autumn in every zone, they want the same full sun and free-draining soil.
• Everlasting daisies: a second flower for drying beside Drumstick, happy in the same lean bed.
• Asters: tall China aster types add long-stemmed cut flowers to a spring-sown picking bed.
• Vegetable beds: the flowers draw bees and beneficial insects into the garden.

Keep apart

• Sunflowers on the sunny side: a tall row there leaves scabiosa in shade for much of the day.
• Zucchini and other thirsty, heavily fed crops: the water and feed they need is more than scabiosa wants.

Harvesting Blooms

Cut sweet scabious when the flowers are almost fully open, and Drumstick when its seed heads are light green with bronze edges.

• Take each stem at full length, snipping just above a leaf pair.
• Pull off any leaves that would sit under water, and get stems into a clean bucket as you go.
• Cut Drumstick as the star-shaped centres are just turning black, before they fall out.

To dry Drumstick seed heads or 'Atro White', hang small bunches upside down in a dry, dark, well-ventilated room for about two weeks. Keep them away from the damp air of a laundry or bathroom. Use sweet scabious in fresh vases and the dried heads in winter arrangements.

Common problems

Bare rows after sowing. Seed buried deeper than 5 mm, a surface left to dry, or soil far outside 18 to 21°C usually explains it. Read more

Seedlings topple overnight. Damping off (a stem rot of young seedlings, mostly from Pythium species and Rhizoctonia solani) is worst where mix or soil stays wet. Read more

Plants wilt and rot at the base. Waterlogged roots are the cause; the second of the Three mistakes that matter covers the fix.

Flowering stops early. Plants setting seed, or summer heat in warm zones, slow new buds; deadhead as set out in Deadheading.

Pests and diseases

Serious trouble is rare: snails go for young plants, and sap-suckers multiply on stressed ones.

Garden snail (Cornu aspersum) and grey field slug (Deroceras reticulatum). After dark, and most of all on wet nights, they strip seedlings and tender tips and leave silvery trails. Go out with a torch about two hours after sunset to collect them, and sink beer traps nearby. Read more

Aphids (family Aphididae). These small sap-suckers crowd new shoots and leave sticky honeydew. Hose them off with a strong jet of water, or spray insecticidal soap onto the undersides of the leaves. Read more

Two-spotted mite (Tetranychus urticae). Leaves turn yellow and finely stippled as numbers climb in hot, dry spells. Blast the leaf undersides with the hose and keep plants from drying out. Read more

Western flower thrips (Frankliniella occidentalis). They hide in buds and growing tips and leave flowers scarred and misshapen. Remove spent and damaged flowers, and hang blue sticky traps near the plants. Read more

Prevention first

• Give plants the full spacing from Sowing Seeds, so foliage dries fast after rain.
• Aim the hose at the roots in the morning, leaving the leaves dry.
• Start each tray sowing in new mix and a scrubbed tray.
• Look over new shoots and buds once a week while plants are flowering.

Tips

1. Sow two or three batches three or four weeks apart for a longer run of flowers.
2. Grow 'Tall Double Lavender Blue' at the back of a border, where its 90 cm stems rise above lower plants.
3. Sweet scabious is naturalised in parts of southern Australia, including South Australia, and its seed can persist in the soil. Ask your council whether it counts as a local weed before you let heads ripen.