How to Grow Capsicums in Australia

Capsicum (Capsicum annuum) is a frost-tender plant in the nightshade family, Solanaceae, grown for sweet, thick-walled fruit eaten green or fully coloured. Sweet types carry a recessive gene that stops them making capsaicin, the compound that makes a chilli hot. It is a long-season crop that rewards warm soil and steady water, and planting out too early is the usual failure.

Three mistakes that matter

1. Planting out into cold soil. Seedlings set out before the soil reaches about 18°C just sit there, and growth is held back below 10°C. Keep them under cover until the last frost has passed and the nights stay mild.
2. Watering in fits and starts. A dry spell drops flowers and buds, and uneven moisture brings blossom end rot to the swelling fruit. Water deeply and regularly, about 25 mm a week, under straw mulch.
3. Feeding for leaves, not fruit. Too much nitrogen builds a big, soft green bush that sets few fruit. Feed gently until the first flowers, then switch to potassium, as Care by growth stage sets out.

When to plant

Capsicum seed germinates best at 25°C to 30°C and very slowly below 20°C. Raise it in trays on a seedling heat mat or in a warm room. Plant seedlings out once the soil holds at least 18°C and frost has passed. One sowing usually does, because plants keep cropping from summer well into autumn.

Where frost ends late, start seed 6 to 10 weeks before the last frost so plants are about 10 cm tall at planting time. In the tropics, plant out as the wet season ends, so plants flower before the build-up heat.

Site, soil and setup

Capsicums want full sun and shelter from wind, because their brittle branches snap under a heavy crop. Where summers are hot and dry, a light shadecloth over the bed on scorching days protects the fruit from sunscald.

Container growing

One plant needs a pot at least 30 cm across, holding 13 L or more. Large bell types do better in a 40 cm pot of about 28 L. Fill it with premium potting mix blended with compost. Compact types suit pots best: the 'Snack' hybrids, and 'Yolo Wonder' and 'Sweet Banana' at about 60 cm tall.

• Water: daily in hot, dry weather, until it runs from the base.
• 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 against a warm wall, out of the wind.
• Support: a short cane pushed in at planting, with the main stem tied to it.

Sowing Seeds

Start seed in punnets or cell trays under cover, then plant out once the weather warms. Direct sowing works only where the soil is already warm. Due to quarantine restrictions and our shipping policy, we cannot send capsicum seeds to Western Australia.

Starting under cover

• Sow 5 mm deep in seed-raising mix.
• Keep the mix just moist and warm (see When to plant); seedlings show in 7 to 21 days.
• Give full light as soon as they emerge, so they do not turn leggy.
• At 4 to 5 weeks, move them into larger pots if planting out is still weeks away.

Planting out

• Harden off (accustom seedlings to sun and wind) over about a week.
• Plant at the depth they grew in the pot.
• Space plants 40 to 50 cm apart in rows 1 m apart; in cool gardens, 70 cm lets more sun warm the soil.
• Water in with half-strength seaweed solution and mulch with straw, clear of the stems.

Pollination

Each capsicum flower carries both pollen and stigma, so it can pollinate itself and a single plant sets fruit. Bees still help: plants they visit tend to set larger fruit with more seed.

When fruit fails to set, temperature is usually the cause. Pollen suffers below 15°C and above 32°C, and two days at 33°C while buds open cuts fruit set. Hot, dry weather drops flowers and small fruit.

• On still days or under cover, tap each flowering stem gently around midday to shake the pollen loose.
• Or swirl a small, soft paintbrush inside each open flower in turn.
• Grow flowers nearby to bring bees to the bed.

Care by growth stage

Warmth, steady water and a switch from nitrogen to potassium at flowering decide this crop. Weeks count from planting out.

If you prefer a conventional feed, 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 until flowering, then a fruiting and flowering soluble (NPK around 15-4-26). Use each at its label rate.

Pruning and Training

Capsicums need little pruning, but they need support, because stems turn brittle and a laden branch splits in wind. Put the stake in at planting, before the roots spread.

• Stake: a sturdy stake or cane beside each plant, or a short cage for bushy types.
• Ties: tie the main stem loosely with soft ties as it grows, and tie in heavy side branches.
• First flowers: pinch off the earliest buds on small plants, so they build a frame before they carry fruit.
• Growing tip: pinching it out at about 30 cm is optional; it gives more, smaller fruit, a little later.
• Leaves: leave them on, since they shade the fruit from sunscald.
• Damage: cut wind-broken branches back cleanly to a healthy fork.

Companion planting

The best partners feed the insects that eat capsicum pests, or break the wind.

Grows well with

• Sweet alyssum between plants, whose flowers draw hoverflies; hoverfly larvae eat aphids and thrips.
• Coriander and dill left to flower, which draw ladybirds and parasitic wasps.
• Nasturtium, a trap crop that draws aphids off the plants; squash the colonies it collects.
• Basil, low enough to fill the gaps in the same warm, watered bed.
• Tall forage sorghum sown to windward two to three weeks before planting, as a windbreak.

Keep apart

• Tomato, which shares Queensland fruit fly (Bactrocera tryoni), bacterial spot (Xanthomonas species) and tomato spotted wilt virus.
• Potato, which shares potato virus Y and tomato spotted wilt virus.
• Eggplant, which shares broad mite and root-knot nematode (Meloidogyne species).

Harvesting Fruit

Pick bell types green once they reach full size and feel firm and glossy, usually 10 to 12 weeks after planting out. Left on the plant for another 2 to 3 weeks, they colour and sweeten.

• Cut the stalk with secateurs or a sharp knife; pulling tears the brittle branches.
• Pick often, since fruit left to colour slows the next fruit.
• Remove overripe fruit promptly, because soft fruit draws pests.
• Before the first frost, pick everything, or pull the whole plant and hang it under cover.

Part-coloured fruit keep colouring in a warm room. Keep the rest in the crisper drawer of the fridge. Green fruit held long below about 7°C pit and soften, and coloured fruit tolerate the cold better.

Eat them raw, roast and peel them, or slice and freeze them without blanching.

Common problems

Blossom end rot. A sunken, leathery patch at the base of the fruit, caused by uneven watering; see Three mistakes. Lime belongs in bed preparation, not as a cure. Read more

Sunscald. A pale, soft patch on the sunny side of the fruit that dries white and papery, where fruit lost its shading leaves. See Site, soil and setup for shade.

Small or misshapen fruit. Poor pollination in cold or heat leaves fewer seeds, and fruit with few seeds stay small or deformed; see Pollination.

Fruit slow to colour. Coloured fruit need weeks longer on the plant than green ones, and cool autumn weather slows them further. In cool gardens, pick the last fruit green.

Pests and diseases

Watch for four insects, a mite and a bacterial disease, and for the viruses aphids and thrips spread.

Queensland fruit fly (Bactrocera tryoni). Females sting ripening fruit and the maggots tunnel through the flesh, which rots fast. It reaches Canberra late in the season. Slip exclusion bags over young fruit or net whole plants, and freeze stung fruit in a sealed bag for two days before binning it. Read more

Tomato grub (Helicoverpa armigera). Also called cotton bollworm or corn earworm, and managed the same way as the look-alike native budworm (Helicoverpa punctigera). Caterpillars up to 40 mm bore into buds and fruit, which then rot. Check the top of the plant for eggs and small grubs and squash them; Bt (Bacillus thuringiensis) sprays work best on young caterpillars.

Green peach aphid (Myzus persicae). Colonies on shoot tips distort new growth, but the greater harm is the viruses it spreads, such as potato virus Y. Hose small colonies off or use insecticidal soap. Read more

Western flower thrips (Frankliniella occidentalis). Thrips silver the leaves and scar the fruit, and they spread tomato spotted wilt virus, which has no cure. Pull and bin infected plants, and where the virus is common, grow a hybrid bred for it, such as 'Hustler'. Read more

Broad mite (Polyphagotarsonemus latus). Too small to see, it feeds in the shoot tips, leaving new leaves stiff, bronzed and curled under at the edges, much like herbicide damage. Remove the worst plants and spray the rest with wettable sulphur.

Bacterial spot (Xanthomonas species). Small, sunken leaf spots merge until leaves yellow and drop, and young fruit carry raised scabs. It spreads in rain splash and on seed, so water the soil, not the leaves; copper fungicide protects new growth in wet weather.

Prevention first

• Bag or net fruit from the first set wherever fruit fly is active.
• Water the soil in the morning and keep the leaves dry.
• Check shoot tips and open flowers each week for aphids, thrips and grub eggs.
• Pull sowthistle and other weeds that shelter aphids, thrips and the viruses they carry.

Tips

1. In frost-free tropical gardens, capsicum grows as a short-lived perennial, and the variety 'Perennial' can crop for several years.
2. In Melbourne and other cool gardens, a potted plant kept barely moist under the eaves over winter can reshoot in spring and crop earlier.
3. Sweet and hot types planted together do not make the fruit on the plant hot, but insects can cross them. Save seed only from open-pollinated varieties grown well apart, since F1 hybrids do not come true.