How to Grow Coreopsis in Australia

Coreopsis, or tickseed, is a sun-loving daisy of the family Asteraceae, grown for yellow, gold and red flowers from late spring into autumn. The annual calliopsis (Coreopsis tinctoria) flowers in its first summer, while the large-flowered perennials (Coreopsis grandiflora and Coreopsis lanceolata) return for a few years. All of them handle heat and dry spells and feed bees and butterflies. The usual mistakes are burying the seed and too much kindness: rich soil, heavy feeding and constant water.

Three mistakes that matter

1. Burying the seed. Light helps coreopsis seed germinate, so seed sown deep often never comes up. Press it onto damp soil and cover it no deeper than the variety table under Sowing Seeds shows.
2. Rich soil and wet feet. Fertile, heavily fed beds grow soft stems that sprawl and flop, and crowns sitting in soggy ground can rot. Choose lean, free-draining soil and keep to the light feeding in Care by growth stage.
3. Leaving spent flowers. Plants left to set seed flower for a shorter season, and the seed spreads well beyond the bed. Trim them as set out in Deadheading, and read the Tips if you garden near bushland.

When to plant

Sow once the soil sits between 15 and 24°C, and expect seedlings in one to four weeks. Every zone has an autumn window, with Anzac Day inside it in the south, and a late winter to spring window. Sow Dwarf Radiata Mixed in both windows for a longer run of colour; the perennials need sowing only once.

Where frost lingers into spring, start seed in trays under cover about six weeks before the last frost and plant out once it passes. Seed sown late in a window meets hot weather young, so water it regularly until it is established.

Site, soil and setup

Give coreopsis full sun, at least 6 hours a day, and light, free-draining soil. Poor, sandy or rocky ground suits it, and soil anywhere from acid to neutral needs no correcting. The perennials stay put for several years, so choose a spot that will not be dug over.

Container growing

Dwarf Radiata Mixed and Sunray, at about 45 to 60 cm tall, suit pots better than the taller Mayfield Giants. Choose a pot that holds at least 10 L; one 30 cm across holds about 13.5 L. It needs drainage holes. Potting mix can carry Legionella bacteria, so wear a mask and gloves to handle it and wash your hands afterwards.

• Watering: once the top of the mix feels dry, soak it until water drips from the base.
• Feeding: potted plants run short of food sooner. From the first buds, give fish and seaweed blend at 25 mL per 9 L each fortnight.
• Position: the sunniest spot you have, in a heavy pot that wind will not tip.

Sowing Seeds

Coreopsis comes readily from seed sown straight into the bed, or in trays for an earlier start where frost lingers.

Sowing direct

• Rake the soil fine and level, water it, then press the seed onto the damp surface.
• Cover it with fine soil to the depth in the variety table below, and no deeper.
• Keep the surface damp, never wet or dry, until seedlings show in one to four weeks.
• Thin to the spacing in the table once the first true leaves open.

Starting in trays

• Sow into punnets of fresh seed raising mix, at the same depth as in the bed.
• Stand them somewhere warm and bright, and keep the mix evenly damp.
• Transplant once seedlings carry true leaves and stand 5 to 10 cm tall.
• Harden off the seedlings first (give them more time outdoors each day for about a week, until they cope with sun and wind).
• Settle each one in with half-strength seaweed solution, 15 mL per 9 L.

All three varieties share one method, but depth, height and life span differ. The perennials flower in their first summer from an early sowing, then usually return for two or three years.

Care by growth stage

Coreopsis flowers best on lean rations: a deep soak now and then once established, and very little feed. Most of what it needs comes from the compost dug in before sowing.

If growth stalls in thin, hungry soil, scratch in a light dose of all-purpose controlled release granular (NPK around 14-5-10) at the label rate.

Deadheading

Flowers left to set seed slow the next flush, so regular trimming keeps plants blooming from late spring into autumn.

• Every few days: snip faded flowers back to the next bud or pair of leaves.
• Young plants: pinch out the growing tips for bushier plants with stronger stems and more flowers.
• Picking for the vase: counts as deadheading, so cut often.
• Sprawling perennials in summer: cut them back hard to the fresh leaves at the base, and they regrow.
• Perennials in winter: cut back to about 5 to 8 cm above the ground.
• End of season: pull out spent Dwarf Radiata plants and compost them before seed drops.

Companion planting

Coreopsis suits a sunny, lean bed shared with other flowers that dislike rich soil and wet feet.

Grows well with

• Everlasting daisies: they want the same light, sandy soil and a deep soak only when it is dry.
• Lavender: lean, free-draining soil and little water once established suit both.
• Cornflowers: they tolerate poor soil and need only light feeding.
• Marigolds: another light-feeding daisy for the front of a sunny border.
• Vegetable beds: the flowers draw bees and beneficial insects to the garden.

Keep apart

• Zucchini and pumpkins: heavy feeders that need 25 mm of water a week or more, far more than coreopsis wants.

Harvesting Blooms

Cut coreopsis once the flowers have opened, early in the morning while stems are full of water.

• Carry a bucket of water to the bed and stand stems in it as you cut.
• Use sharp, clean snips, cutting each stem just above a pair of leaves.
• Strip any leaves that would sit below the water line, as they rot and foul it.

Keep cut stems somewhere cool and out of the sun until they go into a vase, since warmth shortens their life. Use them in mixed posies, or leave some on the plant to feed the bees.

Common problems

Bare rows after sowing. Seed that dried out, sat in cold soil or was buried too deep, as Three mistakes that matter explains, usually accounts for it. Read more

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

Perennials fade after a few years. Both perennial species are short-lived, often lasting two or three years, so sow fresh seed or keep a few self-sown seedlings to follow on.

Seedlings everywhere. Coreopsis self-seeds into any bare ground nearby, so pull unwanted seedlings while they are small.

Pests and diseases

Established plants shrug off most trouble; snails take seedlings, and damp or crowded plants invite fungal disease.

Garden snail (Cornu aspersum) and grey field slug (Deroceras reticulatum). They feed after dark, most of all on wet nights, chewing seedlings to the ground and leaving shiny trails. Collect them by torchlight about two hours after sunset, or sink beer traps nearby. Read more

Aphids (family Aphididae). These small sap-suckers crowd new shoots, leave sticky honeydew and are drawn to yellow flowers. Hose them off or spray insecticidal soap, and let ladybirds and lacewings do the rest. Read more

Powdery mildew (fungi of the order Erysiphales). White spots on the leaves spread until they coat the whole surface. Remove affected leaves, space plants for airflow and spray early outbreaks with 1 part full-cream milk to 10 parts water. Read more

Grey mould (Botrytis cinerea). In cool, damp weather the flowers rot and grow a grey mould. Pick off affected flowers and water at soil level.

Prevention first

• Keep to the spacing in Sowing Seeds, so leaves dry quickly after rain.
• Water the soil, not the leaves, in the early morning.
• Start tray sowings in fresh mix and scrubbed trays.
• Clear spent flowers and plants, where grey mould spores survive.

Tips

1. Sow Dwarf Radiata Mixed in a close drift at the front of a bed, as the annual calliopsis flowers best when crowded.
2. Mayfield Giants is sold as Coreopsis lanceolata, an environmental weed in New South Wales and Queensland that has spread into grassland around Stanthorpe QLD. Near bushland, deadhead before seed forms and check your council's weed advice.
3. Divide perennial clumps every two or three years in early spring to keep them vigorous.