How to Grow Schizanthus in Australia

Schizanthus (Schizanthus pinnatus and its hybrids, sold as Schizanthus x wisetonensis) is a cool-season annual of the tomato family, Solanaceae. It is grown for pots, bedding and small vases, and its spotted, two-lipped flowers earn the names poor man's orchid and butterfly flower. It is no orchid, though: it comes from Chile, and in most Australian gardens it flowers through the mild months, then fades in summer heat. The usual stumble comes at sowing, when seed that needs darkness is left in the light.

Three mistakes that matter

1. Leaving the seed in the light. Schizanthus germinates in the dark, so an uncovered tray can stay bare. Cover the seed and keep the tray dark until the first shoots show, as set out in Sowing Seeds.
2. Timing the flowers into summer. Plants struggle in summer heat, so a sowing that comes into bloom in January fades early. Keep to your zone's window under When to plant, and give afternoon shade in warm areas.
3. Soggy soil. Roots rot in heavy, wet ground or in pots watered on a schedule rather than by need. Choose free-draining soil or potting mix, and water only once the top 5 cm has dried, as set out in Care by growth stage.

When to plant

Seed comes up in about 5 to 14 days in mix held at 18 to 22°C. Flowering starts about 14 to 18 weeks after sowing, so sow for flowers in mild weather. In frost-free zones, that means late summer and autumn sowings for winter and spring flowers. Plants will not take frost, so where frost is regular, sow in spring and plant out after the last frost.

Early in an autumn window, keep trays in light shade until the heat breaks. In southern gardens, aim to sow autumn trays by Anzac Day, and give spring sowings afternoon shade.

Site, soil and setup

Give schizanthus a sheltered, bright spot with at least 3 hours of direct sun a day, shaded from the hot afternoon sun in warm zones. The soil needs to drain freely and hold plenty of organic matter. Acid, neutral and alkaline soils all suit, so pH rarely needs correcting.

Damping off organisms survive between crops on old plant material. Choose a fresh spot if seedlings collapsed there the season before.

Container growing

Schizanthus is a natural pot plant, and a pot can move into shade on hot days. Allow at least 10 L of potting mix per plant; a 30 cm pot holds about 13.5 L. Use fresh potting mix in a pot with drainage holes. Bagged mix can carry Legionella bacteria. Dampen it before opening, wear a mask and gloves, and wash your hands afterwards. For pots, window boxes and small spaces, choose 'Angel Wings Mixed', at about 40 cm.

• Watering: check daily in warm weather, and water once the mix feels dry just below the surface, until it drains from the base.
• Feeding: from the first buds, water on fish and seaweed blend at 25 mL per 9 L every two weeks.
• Position: morning sun and afternoon shade, out of strong wind.

Sowing Seeds

Trays are the surest start, as the darkness and moisture the seed needs are easy to control there.

Starting in trays

• Fill a punnet with seed raising mix and water it from below until the surface darkens.
• The seed is fine, so mix it with dry sand for an even spread; see sowing tiny seeds.
• Cover with 3 mm of mix, then lay a board or dark lid over the tray.
• Keep the tray at 18 to 22°C and check daily.
• Lift the cover as soon as shoots appear, and move the tray into full light.

Sowing direct

In frost-free gardens, sow 3 mm deep where plants are to flower, 30 cm apart. Lay a board over the row, keep the soil damp and check under it daily. Thin to the strongest seedling at each spot once true leaves open.

Planting out

• Plant out once seedlings have their first true leaves and stand 5 to 10 cm tall.
• Harden off seedlings first (give them more time outdoors each day over a week or two).
• Space plants 30 cm apart, and wait until all danger of frost has passed.
• Water each one in with half-strength seaweed solution, 15 mL per 9 L.

Both varieties are grown the same way and differ mainly in height.

Care by growth stage

Schizanthus is a light feeder that runs on the compost in its bed. What decides it is water: even moisture at the roots, dry leaves, and no standing water.

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

Deadheading

Two jobs keep schizanthus compact and flowering: pinching young plants so they branch, then removing spent flowers before they rot or set seed.

• Young plants: once they are growing strongly after planting out, pinch off the top set of leaves just above a lower pair.
• Every few days in flower: snip faded flowers and spent clusters back to just above a set of leaves.
• Damp weather: clear ageing petals promptly, as grey mould starts in them.
• Cutting for the vase: counts as deadheading, so pick often.
• End of flowering: pull out spent plants and compost any that are free of disease.

Companion planting

Schizanthus suits a bed or pot of cool-season flowers that share its sowing months and its liking for afternoon shade.

Grows well with

• Violas and pansies: sown in late summer and autumn in dark trays, they also take afternoon shade in warm areas.
• Calendula: sown in autumn and again from late winter, it flowers through the same cool months in sun or half sun.
• Vegetable beds: the flowers draw bees, and a patch of flowers helps bring beneficial insects into the garden.

Keep apart

• Tomatoes and other nightshade crops: relatives share whitefly and aphids, which move between them.
• Petunias in the same pot: they want summer heat and full sun, the conditions in which schizanthus fades.

Harvesting Blooms

Cut stems for the vase when the first few flowers on a cluster have opened and the rest are still in bud.

• Cut in the cool of the morning, while stems are full of water.
• Take the longest stems you can, cutting just above a set of leaves.
• Strip any leaves that would sit below the water line.
• Stand the stems in a clean bucket of water straight away.

The flowers last well in fresh arrangements. Keep the vase cool and out of direct sun, and change the water every couple of days. A potted plant in full flower can also come indoors to a bright, cool room.

Common problems

Bare trays after sowing. Seed left in the light, buried deeper than 3 mm, or kept too hot or cold usually explains it. Read more

Tall, pale seedlings that flop. They are stretching for light, often because the cover stayed on after shoots appeared. Read more

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

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

Flowering stops early. Summer heat or spent flowers left to set seed slow new buds; see Deadheading.

Pests and diseases

Sap-suckers and grey mould cause most of the trouble, and snails go for young plants.

Aphids (family Aphididae). Small sap-suckers crowd soft shoot tips and the undersides of leaves, leaving sticky honeydew. Knock them off with a firm jet of water, or spray insecticidal soap onto the colonies. Read more

Greenhouse whitefly (Trialeurodes vaporariorum). Tiny white insects rise in a cloud when a plant is brushed, and leaves yellow. Hang yellow sticky traps and spray insecticidal soap under the leaves, repeating every few days. Read more

Western flower thrips (Frankliniella occidentalis). They rasp at buds and petals, leaving silvery streaks and distorted flowers. Hang blue sticky traps and clear weeds and spent flowers where they breed. Read more

Grey mould (Botrytis cinerea). Fading petals turn soft and brown, then grow grey fuzz, most often in cool weather with heavy dew. Remove affected flowers at once and water at soil level, never over the plant.

Garden snail (Cornu aspersum) and grey field slug (Deroceras reticulatum). They graze seedlings overnight and leave silver trails. Go out with a torch about two hours after sunset to collect them, and set beer traps nearby. Read more

Prevention first

• Give plants the full 30 cm spacing so leaves and flowers dry quickly.
• Water at the base in the morning, keeping flowers and leaves dry.
• Start each tray sowing in fresh mix and a scrubbed tray.
• Turn a few leaves and check the shoot tips once a week.

Tips

1. In frost-prone gardens, stand potted plants under a verandah or against a north-facing wall on cold nights.
2. Sow a second tray three or four weeks after the first for a longer run of flowers.
3. Where frost ends late, plant out around Melbourne Cup weekend, the traditional marker for frost-tender plants in cool gardens.