How to Grow Liatris in Australia

Liatris (Liatris spicata), also called blazing star or gayfeather, is a summer-flowering perennial in the daisy family (Asteraceae). It is native to the prairies and meadows of eastern North America. Its tall purple spikes open from the top down, last well in a vase, dry for winter arrangements and draw bees and butterflies. It copes with cold winters and hot summers everywhere outside the tropics. Wet soil around the dormant corms (swollen underground stem bases that store food) can rot them.

Three mistakes that matter

1. Planting into wet ground. Boggy soil rots the corms, most often over a cold, wet winter while the plant is dormant. Choose free-draining soil or a raised bed, and never plant where water lies after rain.
2. Letting the soil dry out while spikes grow. Liatris has shallow roots that can die if the soil dries during the growing season. Keep the soil evenly moist from the first shoots until flowering ends.
3. Cutting stems to the ground. The leaves on the lower stem feed the corm for next summer. When cutting for the vase, leave at least 10 cm of stem and its leaves standing.

When to plant

Plant dormant corms from late winter into spring, as the soil starts to warm and the worst frosts pass. The corms themselves are frost hardy, and shoots appear once the soil warms. One planting flowers year after year, so there is no need to plant in succession.

Corms usually flower the same summer they go in, often 10 to 13 weeks after planting, and later where the soil is still cold.

Site, soil and setup

Liatris evolved in harsh prairie conditions, so lean, well-drained soil in full sun suits it better than a rich, damp bed.

Crop rotation does not apply to a perennial that stays put for years, so divide the clump instead, as described under Tips.

What the state weed lists say

No state or territory outside Western Australia lists liatris as a declared or noxious weed. Western Australia keeps one register for every organism, so check the species' entry there.

Container growing

Liatris grows well in a large pot, which also solves the drainage problem on heavy clay. For three corms, use a pot at least 30 cm across, about 12 to 15 L, with several large drainage holes. Fill it with premium potting mix. Tall spikes catch the wind, so choose a heavy pot that will not tip. Compact varieties, such as purple 'Kobold' and white 'Alba', suit smaller pots.

• Position. Full sun, out of the strongest wind.
• Watering. Water once at planting, then again when shoots appear. Potting mix dries out faster than garden soil, so check it every few days in summer.
• Feeding. Give seaweed solution at 30 mL per 9 L every fortnight from the first shoots until the first flowers.
• Winter. Move the pot under cover in a wet winter so the dormant corms stay on the dry side.

Planting Corms

Liatris starts from a corm, sold as tubers, planted flat side down in late winter or spring.

Before planting

Plant only firm corms, and discard any that are soft or mouldy. Until planting, store them in a cool, dry, airy spot.

Planting in the ground

• Set each corm flat side down.
• Plant 5 to 10 cm deep.
• Space corms 15 to 30 cm apart, closer for a fuller look the first summer.
• Plant in groups of three or more, which look better than single spikes.
• Water in once so the soil is moist but not saturated.
• Water again once shoots appear, or sooner in a long dry spell.

Care by growth stage

Water decides the result: moist soil while the plant is in leaf and flower, and dry soil while it rests in winter. Liatris is not a heavy feeder, and rich feeding gives soft, leaning stems.

Week ranges count from planting and stretch in cool districts. If growth stalls in poor soil, scratch a light dose of all-purpose controlled release granular (NPK around 14-5-10) into the soil as shoots appear.

Companion planting

Liatris adds a vertical line to a sunny border and mixes well with plants that like the same lean, well-drained soil.

Grows well with

• Coreopsis and cosmos, whose yellow and open flowers contrast with the purple spikes in full sun.
• Echinacea, another prairie plant that flowers alongside it and feeds the same bees and butterflies.
• Lamb's ear and ornamental grasses, low growers that leave the spikes in sun and suit dry soil.

Keep apart

• Thirsty plants on daily watering, because constantly wet soil rots the corms.
• Trees and tall shrubs that shade the bed, because shade makes stems stretch and flop.

Harvesting Blooms

Cut spikes for the vase when the top 5 cm of flowers are fully open. Spikes cut earlier do not keep opening downwards in water.

• Leave at least 10 cm of stem, with its leaves, on the plant.
• Stand cut stems in a bucket of water straight away.
• Change the vase water every few days.
• On plants left in the garden, snip off each spike once it fades.

Cut stems can last up to 2 weeks indoors when the water is changed regularly. To dry spikes, cut them when half to two thirds of the flowers are open. Hang them upside down in a dry, shaded, airy spot for about 3 weeks. Drying them in silica gel or sand holds more colour.

Common problems

Floppy stems. Soil that is too rich or a spot that is too shady makes stems shoot up soft and lean. Move the clump to full sun when you next divide it, and prop tall stems with a thin stake meanwhile.

Soft, rotten corms. Waterlogged soil is the cause, as described in Three mistakes that matter. Read more

Scorched leaves and flower tips. Hot, dry wind while the spikes are lengthening, such as a summer northerly, can wilt plants beyond recovery. Water deeply before hot days and plant out of the worst wind.

A dead centre in an old clump. Older clumps can die out in the middle, and dividing them, as described under Tips, keeps them vigorous. Read more

Pests and diseases

Liatris is generally trouble free. These four are the ones to watch for.

Thrips (order Thysanoptera). These tiny insects, 1 to 2 mm long, suck sap and leave mottled or silvery-brown speckling on leaves and flowers, mostly during flowering. Rinse plants, including leaf undersides, and spray insecticidal soap weekly for four to six weeks. Read more

Aphids (family Aphididae). Small sap-sucking insects cluster on soft new growth and leave sticky honeydew. Hose off light infestations, and spray horticultural oil or soapy water on heavy ones, but never in hot weather. Read more

Powdery mildew (Golovinomyces species). A white powdery film covers the leaves, often in hot, humid weather when plants go into the night wet. Spray 1 part full-cream milk to 10 parts water on the leaves, and remove badly affected ones. Read more

Grey mould (Botrytis species). A fuzzy grey rot can attack the flowers in wet weather, or corms in storage. Snip off affected spikes, and plant only firm, clean corms.

Prevention first

• Keep the spacing given under Planting Corms, so sun and air reach every plant.
• Water the soil in the morning rather than the leaves at night.
• Spare ladybirds and lacewings, which eat thrips and aphids, by spraying only where pests are.
• Clear spent spikes and dead leaves as part of everyday garden hygiene.

Tips

1. Push a label in beside each clump at planting, because nothing shows above ground through winter.
2. Leave a few bronzed stems standing over winter for structure, then cut everything to the ground in early spring before new shoots appear.
3. Lift and divide clumps every three years or so, in late autumn or winter while they are dormant. Cut the tuberous roots with a sharp knife, keeping at least one bud on each piece, and replant straight away.

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