How to Grow Eggplant in Australia

Eggplant (Solanum melongena) is a frost-tender member of the nightshade family, Solanaceae, grown for its glossy fruit. It loves the long, hot summers of northern and inland Australia, and still crops in the south when raised early under cover. The usual failure is planting out too soon, because a chilled plant seldom recovers.

Three mistakes that matter

1. Planting out into cold ground. Seedlings set out into cold soil or chilly nights stall and seldom recover. Keep them growing in pots under cover until the cue in When to plant.
2. Letting the soil dry out between drinks. Dry spells make the plant shed flowers and young fruit, and uneven moisture brings bitter fruit and blossom end rot. Mulch, and water deeply on a regular schedule, as set out in Care by growth stage.
3. Leaving fruit on the bush too long. Once the skin dulls, the seeds harden and the flesh turns spongy and bitter. Pick at about two-thirds of full size while the skin still shines, and the plant keeps flowering.

When to plant

Eggplant seed germinates in soil at 24°C to 32°C, so sow in trays on a heat mat and plant out 8 to 10 weeks later. Plant out once the soil holds 20°C and nights stay above 10°C. In the tropics and subtropics, a second sowing a month after the first can stretch the picking season.

In Hobart, Canberra and the tablelands, long slim and small-fruited types crop earlier than big globes, which makes them the safer choice.

Site, soil and setup

Eggplants want full sun and deep, free-draining soil that warms quickly in spring. Sandy loams suit them best; heavy clay stays cold and wet.

Rotation matters more for eggplant than for most crops, because verticillium wilt survives in soil for years. Peas and beans make good crops to rotate with.

Container growing

One plant needs a pot at least 40 cm across, holding about 28 L, with a stake or small tomato cage set in at planting. Fill it with premium potting mix, or 3 parts potting mix to 1 part coir peat and 1 part washed river sand. Compact types suit pots best: the container-bred 'Kaberi F1' needs no stake, and 'Mini Lebanese', 'Rosalina F1' and 'Turkish Orange' stay small.

• Water: check every day in summer and water until it drains; dry mix spoils the fruit.
• Feed: fish and seaweed blend at 25 mL per 9 L fortnightly, then liquid potash per label fortnightly from the first flowers.
• Position: full sun out of strong wind; a pot can move to shelter when a cold snap threatens.
• Fresh mix: fresh potting mix in a clean pot each season lowers the risk of soilborne wilt.

Sowing Seeds

Start seed in trays under cover, where bottom heat holds the soil warmth germination needs.

Starting under cover

• Sow 5 mm deep in punnets or cells of seed-raising mix.
• Keep the mix warm on a heat mat, as in When to plant, and moist but not wet; seedlings appear in 7 to 14 days.
• Give bright light from directly overhead, or the stems stretch and lean.
• Once true leaves show, keep the strongest seedling in each cell.
• Feed weekly with worm casting liquid diluted to weak tea colour.
• Some F1 seed, such as 'Midnight F1', is fungicide-coated: never eat it, wear gloves, wash afterwards and keep it from children and animals.

Planting out

• Plant out 8 to 10 weeks after sowing, at 10 to 12 cm tall with six or seven leaves.
• Harden off (accustom seedlings to sun, wind and less water over one to two weeks) first.
• Space plants 45 to 70 cm apart, closer for small types, in rows 80 to 100 cm apart.
• Set each plant at the depth it grew in its pot, not deeper.
• Plant in the late afternoon or on an overcast day, and water in with seaweed solution at 30 mL per 9 L.
• Mulch with straw once the soil is warm, keeping it 5 to 7 cm clear of the stem.

Pollination

Eggplant flowers pollinate themselves, though bees buzzing the pollen loose help. Flowers that drop without setting fruit usually point to heat above 32°C, cold nights, dry soil or too much nitrogen. Thrips feeding in the flowers cause the same loss.

Under insect netting, or when fruit set is poor, pollinate by hand.

• Lift the netting every few days while flowers are open, and reseal it each time.
• Dab the centre of each open flower with a soft, dry artist's brush.

Care by growth stage

Warmth, steady water and potassium decide this crop. Weeks count from planting out.

That 25 mm is 25 L per square metre; sandy soils take less at a time, more often. If you prefer a conventional feed, use each at its label rate. Mix a controlled release granular (NPK around 14-5-10) into the bed at planting. Water on an all-purpose soluble (NPK around 23-4-18) fortnightly while plants branch. From the first flowers, switch to a fruiting and flowering soluble (NPK around 15-4-26).

Pruning and Training

Eggplants need little pruning: in a university trial, cutting plants to two or four stems gave no consistent gain over staked, unpruned plants.

• Pinch off any flowers that open on seedlings before planting out.
• On large-fruited types, keep three main stems forking from the base and rub out weaker shoots.
• On long types such as 'Long Purple', pinch the tip at about 45 cm to encourage branching.
• Tie each main stem to the stake with soft ties as the fruit loads up.
• Remove pale, spotted or yellowing leaves and bin them rather than composting them.
• Leave enough leaf over the fruit to shade it from sunscald.

Companion planting

Short crops and pollinator flowers suit eggplant; nightshades and other wilt hosts belong elsewhere.

Grows well with

• Dwarf beans, a low crop for the gaps between young plants.
• Lettuce, picked from between the rows before the eggplant canopy closes.
• Mexican marigold (Tagetes lemmonii) nearby, whose flowers draw pollinators and whose scented leaves confuse some flying pests.

Keep apart

• Potato, which shares 28-spotted ladybird and verticillium wilt.
• Strawberries, another host of verticillium wilt.
• Thornapple and other nightshade weeds, which carry eggfruit caterpillar between crops.

Harvesting Fruit

Picking starts 8 to 12 weeks after planting out, once the fruit is full-coloured, firm and glossy.

• Cut the stalk with secateurs, leaving a short stub on the fruit; pulling damages fruit and plant.
• Wear gloves, since many types carry sharp spines on the calyx, stems and leaves.
• Pick in the cool of the morning, at least once a week.
• Remove old, dull or yellowing fruit so the plant keeps flowering.

Eggplant does not store well. It keeps 5 to 7 days at 7°C to 10°C in a humid crisper, and longer chilling pits the skin.

Grill, bake or fry slices, add small types to curries, or char whole fruit for dips. Plain eggplant bottled at home has caused botulism, so freeze blanched slices, or pickle only by a tested method such as CSIRO's preserving advice.

Common problems

Flowers fall without setting fruit. A stressed plant drops its flowers; see Pollination for the causes and the fix.

Dark, sunken patch at the flower end. Blossom end rot: uneven watering starves the swelling fruit of calcium, so steady water prevents it, and lime does not cure an outbreak. Read more

Patches or spots on the fruit. Pale, dry patches are sunscald on fruit left bare by sparse leaves in hot, dry weather; shade plants through a heatwave. Round, sunken spots on ripening fruit are anthracnose (Colletotrichum species), a wet-weather fungus; bin spotted fruit.

Small round holes in the leaves. Flea beetles, tiny beetles with a dark blue metallic sheen that jump when disturbed; a fine insect net keeps them off young plants.

Sudden wilt and collapse in the Top End. Bacterial wilt (Ralstonia solanacearum) lives in red soils around Darwin and light soils near Katherine. Bin affected plants and grow on in clean pots.

Plants wilt, yellow and stay stunted. Root-knot nematode (Meloidogyne species) knots the roots, worst in sandy soil. Bin affected roots, never compost them, and rotate beds. Read more

Pests and diseases

Eggplant shares most of its pests with tomato and capsicum.

Queensland fruit fly (Bactrocera tryoni). Eggplant is on its host lists. Females lay eggs through the skin, leaving pin-prick marks, and maggots rot the flesh. Freeze stung fruit in a sealed bag for two days before binning it. Read more

Eggfruit caterpillar (Sceliodes cordalis). A moth found throughout Australia that lays eggs mainly on the calyx. Its larvae, up to 20 mm long, tunnel through the fruit, often showing only as a 3 to 4 mm exit hole. Bin infested fruit.

28-spotted ladybird (Epilachna vigintioctopunctata). Orange-brown, 6 to 10 mm long, with 28 black spots; adults and spiny, creamy-yellow larvae chew the leaves. Squash them, and the yellow egg clusters under leaves.

Two-spotted mite (Tetranychus urticae). Tiny sap-suckers that multiply in hot, dry weather, leaving pale mottling and fine webbing under leaves. Hose both sides of the leaves, and avoid sprays that kill predatory ladybirds and mites. Read more

Silverleaf whitefly (Bemisia tabaci). Tiny white-winged insects suck sap under the leaves and leave sticky honeydew that grows sooty mould. Numbers climb fast in spring and summer, so act early. Read more

Verticillium wilt (Verticillium dahliae). Often the most serious eggplant disease: leaves yellow, curl inward and wilt, and a cut lower stem shows brown streaks. Nothing cures it, so bin the plant and rotate beds.

Prevention first

• Net plants with fine insect mesh from fruit set, sealed to the ground and held clear of the fruit.
• Check under the leaves weekly for eggs, mites and whitefly, and the shoot tips for aphids.
• Pick up fallen and stung fruit, and never compost it untreated.
• Pull spent plants after the last pick, and clear the weeds named under Companion planting.

Tips

1. To save seed, leave a fruit of an open-pollinated variety until it turns yellow, since F1 seed gives variable plants. Blend it with water, let the seed sink, then sieve and dry it.
2. Salting is worth the trouble only for big purple fruit left past its best; young fruit of most types cooks well without it.
3. Where wilt keeps returning, grafted seedlings on resistant rootstock are said to be more vigorous and disease resistant.