How to Grow Tomatoes in Australia

Tomato (Solanum lycopersicum) is a frost-tender annual in the nightshade family, Solanaceae, grown for fruit picked ripe from the vine. It crops in every Australian climate zone given warmth, sun and steady water. Most failures trace to two things: seedlings set out into cold soil, and water that comes and goes while fruit is swelling.

Three mistakes that matter

1. Planting out too early. Frost kills tomatoes outright, and seedlings pushed into cold ground sulk for weeks. Wait for the last frost and soil at 16°C before planting out.
2. Watering unevenly. Calcium reaches swelling fruit only in the water a plant draws up. Soil swinging from dry to soaked brings blossom end rot and split skins.
3. Ignoring the growth habit. Spacing, support, pruning and how long a plant crops all follow from whether a variety is determinate (bush) or indeterminate (vining). The packet says which.

When to plant

Tomato seed germinates in soil between 16°C and 35°C and comes up fastest at 21°C to 27°C. Start it under cover four to six weeks before your last frost, then plant out once nights hold above about 10°C. One sowing carries a cool garden; warmer zones can add a second for autumn.

At the cold edge of the window a seedling heat mat holds trays near 21°C, which beats sowing early. Where the season is short, choose an early variety and check its days to maturity.

Site, soil and setup

Give tomatoes the hottest, brightest, best-drained corner you have, sheltered from wind that rocks a staked plant loose. Drive the stake or set the cage at planting, because a stake pushed in later cuts through feeding roots.

Fusarium and verticillium wilt survive in soil as resting bodies for years, and root-knot nematode builds quietly under a bed cropped to one family. Three seasons of corn, beans or onions brings the numbers down.

Container growing

A staked plant needs a pot at least 40 cm across holding about 28 L, with the stake fixed first. Dwarf bush types manage in 30 cm, about 13.5 L, in premium potting mix blended with compost. Compact varieties suit pots: 'Tiny Tim' and 'Window Box Yellow' stay under 40 cm, and 'Totem' reaches 45 to 90 cm.

• Water: daily through summer until it runs from the base, twice on days over 35°C.
• Feed: fish and seaweed blend at 25 mL per 9 L fortnightly, then liquid potash per label from first flowers.
• Position: full sun, out of the wind, against a north-facing wall in cool gardens.

Sowing Seeds

Raise seed in punnets under cover and plant out stocky seedlings. Direct sowing works in the tropics and subtropics once soil holds 16°C.

Starting under cover

• Sow 5 to 10 mm deep in seed-raising mix, two or three seeds per cell.
• Hold the mix at 21°C to 27°C, moist but not wet; seedlings show in 5 to 12 days.
• Thin to the strongest seedling, then pot on individually at the first true leaves.
• Harden off (accustom seedlings to sun and wind over about a week) before planting.

Planting out

• Plant deep, burying the stem to the lowest true leaves; the buried stem roots.
• Lay a leggy seedling on its side in a shallow trench, tip turned up.
• Space 40 to 60 cm apart in rows about 90 cm, tying to the stake at once.
• Water in with seaweed solution at half strength, 15 mL per 9 L.
• Mulch with 5 to 7 cm of straw once soil warms, clear of the stem.

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

Pollination

A tomato flower carries both male and female parts, so it sets fruit on its own pollen. The catch is that pollen sits inside a closed cone of anthers and falls only when the flower is vibrated. Wind does it outdoors. Honeybees cannot, but native blue-banded bees (Amegilla species) grip a flower and shake it.

Flowers drop without setting when the weather turns. Sustained days above about 32°C, or nights below about 13°C, stop pollen working.

• On still, warm mornings, tap the stake or flick each open truss to shake pollen loose.
• Work in the middle of the day, before the heat comes on.
• Grow flowering herbs nearby so native bees are already working the patch.

Care by growth stage

Steady water decides this crop, and the feed turns from nitrogen to potassium as the first flowers open. Weeks count from planting out.

That 25 to 38 mm a week is 25 to 38 L per square metre, and sandy soil wants less at a time, more often. Easing water back once fruit is half grown concentrates flavour.

If you prefer a conventional feed, mix a controlled release granular (NPK around 14-5-10) through the bed at planting. Water on an all-purpose soluble (NPK around 23-4-18) fortnightly while leaf builds, then a fruiting and flowering soluble (NPK around 15-4-26) from first flowers.

Pruning and Training

Everything here turns on one word from the packet. An indeterminate extends a main stem and flowers at every truss until cold stops it. A determinate builds a set frame and is spoiled by pruning.

• Side shoots: pinch out the shoot in the angle between leaf and stem, while it still snaps.
• Tying: loop soft ties around stake and stem every 20 to 30 cm, loose enough to slide.
• Stopping: cut the leader two leaves above the fourth truss outdoors.
• Lower leaves: remove any leaf touching soil, leaving canopy enough to shade fruit.
• Hygiene: prune with clean dry hands and secateurs, never in wet weather.

Companion planting

Good neighbours feed the insects that police aphids and grubs, or keep nightshade troubles away.

Grows well with

• Basil and chives, low plants that fill the ground between stakes without taking light.
• Parsley and dill left to flower, whose flat heads feed hoverflies and parasitic wasps.
• Marigold as a solid block the season before, dug in after two months, which can lower root-knot nematode numbers; scattered plants cannot.

Keep apart

• Potato, capsicum, chilli and eggplant, which share the same wilts, nematodes and psyllid.
• Strawberry, another host of verticillium wilt.
• Fennel, which runs to 2 m and self-seeds through a bed.
• Cabbage and broccoli, heavy feeders competing for the same nitrogen.

Harvesting Fruit

First pick comes 8 to 17 weeks from sowing. Watch for the breaker stage, when colour first breaks from green over a tenth of the skin at most. Fruit picked then ripens indoors, ahead of birds, possums and fruit fly.

• Pick every two or three days once the first truss turns.
• Bend the fruit at the knuckle in the stalk so the calyx stays on.
• In cool gardens, leave fruit longer, as slow ripening builds flavour.
• Take off split or stung fruit at every pick and destroy it.
• At season end, pull whole plants carrying fruit and hang them under cover.

Keep ripe fruit on the bench, out of the sun. Refrigeration below about 13°C stops the aroma compounds forming and turns the flesh mealy. Ripen green fruit in a paper bag with a banana. Use them sliced, roasted, or cooked down for sauce.

Common problems

Blossom end rot. A sunken leathery black patch on the base of the fruit, worst on early fruit and paste varieties. It is a water problem wearing a nutrient costume: calcium travels only in the transpiration stream, so a moisture swing starves the fruit. Even watering brings the later trusses away clean.

Split and cracked fruit. Rain or a heavy watering after a dry spell swells flesh faster than skin can stretch, usually on fruit already colouring.

Flowers fall without setting. Extended heat or cold stops pollen working, as does deep shade or a bed pushed hard with nitrogen. See Pollination.

Leaves rolling upward. Older leaves curl and stiffen in heat, drought, waterlogging or after hard pruning, doing little harm. Read more

Mottled, puckered, thread-thin leaves. Tobacco and tomato mosaic viruses travel in seed, on hands and on tools, with tobacco on the fingers a classic source. Read more

Pests and diseases

Hybrid seed packets mark resistance with capital letters. Heirlooms rarely carry it, and listings here spell it out instead.

Queensland fruit fly (Bactrocera tryoni). Native through eastern Australia, with tomato on its host list, it stings fruit while it is hard and green. Destroy stung fruit by freezing, boiling or bagging it in the sun for a fortnight. Read more

Tomato grub (Helicoverpa armigera). Also called corn earworm. Native budworm (Helicoverpa punctigera) looks the same and is managed the same way. The grub bores a neat hole into green fruit and feeds inside.

Silverleaf whitefly (Bemisia tabaci). Widespread in Queensland and Western Australia, it rises in clouds from a disturbed plant, and its honeydew blackens with sooty mould. Read more

Western flower thrips (Frankliniella occidentalis). The most efficient carrier of tomato spotted wilt virus, which bronzes young leaves and rings the fruit. There is no cure, so pull infected plants. Read more

Two-spotted mite (Tetranychus urticae) and tomato russet mite (Aculops lycopersici). Both explode in hot dry weather. The first speckles leaves and spins webbing; the second is 0.2 mm long and bronzes the stem from the base. Read more

Root-knot nematode (Meloidogyne species). Plants wilt in the afternoon, yellow and stall for no visible reason. The answer is on the roots: lumpy galls 1 to 10 mm across. Read more

Prevention first

• Water the soil in the morning, not the leaves, so foliage dries by night.
• Net with fine mesh after flowers set, held clear of the fruit.
• Turn a few leaves weekly to catch whitefly, mites and thrips.
• Bin spent plants and fallen fruit, and pull nightshade weeds.

Tips

1. Save seed from an open-pollinated variety by squeezing pulp into a jar with a splash of water. Stand it out of the sun three days, then rinse and dry the seed that sinks.
2. In Western Australia and Victoria, where tomato-potato psyllid is established, look for white sugar granules on leaves and cupped, narrow, upright new growth. Report suspect plants to your state department.
3. Buy two varieties rather than two plants of one: an early determinate and a late indeterminate spread the picking.