How to Grow Lettuce in Australia

Lettuce (Lactuca sativa) is a fast annual in the daisy family, Asteraceae, grown for crisp or buttery leaves picked over several weeks. In most Australian gardens it grows in every month, with winter the reliable season and summer the one that needs shade. The usual failure is a dry bed, which turns the leaves bitter and sends the plant to seed.

Three mistakes that matter

1. Burying seed in hot soil. Lettuce seed wants cool soil, see When to plant, so a deep midsummer sowing rots or sits idle. Barely cover the seed and sow in the cool of the evening, under shade.
2. Letting the bed dry out. Lettuce roots run shallow, so a dry spell checks growth, turns the leaves bitter and pushes the plant to bolt (run to seed). Mulch with 5 cm of straw and water often, daily in warm weather.
3. Sowing the wrong type at the wrong time. Cos and crisphead types bolt in summer heat, and a whole packet sown at once matures together. Match the type to the season, and grow a slow-bolt type through summer.

When to plant

Cool, moist soil decides this sowing: seed germinates between 8°C and 27°C, and best between 10°C and 20°C. Sow direct into a moist bed, or raise seedlings in punnets and plant them out at four to six weeks old. A short row every two to three weeks gives a steady supply instead of a glut.

At the hot edge of the window, sow in the evening into pre-watered soil and shade the row, since seed sits idle above 30°C. At the cold edge, plants stand light frost, and a cloche keeps growth moving through a Canberra or Hobart winter.

Site, soil and setup

Lettuce wants full sun in the cool months and morning sun with afternoon shade in summer. Its roots stay shallow, so the top 15 cm is the layer to keep moist and fed.

Fresh manure and a heavy hand with liquid feeds grow soft leaves that snails and aphids find first.

Container growing

A pot or trough at least 30 cm across and deep, about 13 L, holds one hearting lettuce or two or three loose-leaf plants. Fill it with premium potting mix blended with compost. Compact types suit pots best: 'Little Gem', a mini cos, 'Mini Butterhead', and the cut-and-come-again 'Salad Bowl' and 'Lolla Rossa'.

• Water: daily in warm weather, until it runs from the base; check pots twice on hot, windy days.
• Feed: fish and seaweed blend at 25 mL per 9 L fortnightly, or an all-purpose soluble (NPK around 23-4-18) dissolved in water fortnightly.
• Position: morning sun, and the pot moved into afternoon shade through the hottest months.

Sowing Seeds

Sow direct where the bed is ready and the soil is cool, or raise punnets where snails, birds or heat make the open bed risky.

Sowing direct

• Sow 3 to 5 mm deep, barely covered, in rows 30 cm apart; buried seed germinates poorly.
• Keep the surface moist; seedlings show in 7 to 14 days, sooner in warm soil.
• Thin the seedlings in stages; see Thinning for the spacings.
• Cover the row with wildlife-safe netting, white, taut and too fine for a finger, and set snail traps on the day you sow.

Starting in punnets

• Sow into seed-raising mix in a cool, bright spot; in summer keep the punnet in shade until the seedlings are up.
• Plant out at four to six weeks, with a few true leaves, before the roots circle the cell. An overgrown punnet bolts soon after planting.
• Harden off (accustom seedlings to sun and wind over about a week). Plant in the cool of the day and shade new plants for a few days.

Due to quarantine restrictions and our shipping policy, we cannot send miner's lettuce (Claytonia perfoliata), a salad green in the lettuce range, to Western Australia.

Care by growth stage

Steady water and a modest, regular feed decide this crop, because a plant that never stalls stays sweet. Weeks count from sowing direct; punnet seedlings run about four weeks ahead.

Water in the morning so leaves dry before dark, and soak the top 15 cm rather than sprinkling, which pulls roots to the surface. Growth slows through a cold snap, so hold the feed until it picks up again.

Thinning

Thin once seedlings are a few centimetres high, before neighbours shade each other. A crowded hearting type often fails to form a firm head, and the thinnings are the first harvest.

• Loose-leaf types: 15 to 20 cm apart, or left at 10 cm and picked young as baby leaves.
• Butterhead and mini cos: 20 to 25 cm apart.
• Full-sized cos and crisphead: 30 cm apart, in rows 30 to 50 cm apart.
• Method: snip surplus seedlings at soil level rather than pulling them, so the shallow roots of the keepers stay undisturbed.

Companion planting

Lettuce is quick and shallow-rooted, so it pairs with crops that grow slowly, stand tall or root deep.

Grows well with

• Carrot, radish and beetroot, since lettuce fills the gaps and is picked before the roots need the room.
• Sweet corn or climbing beans on the western side, whose shade takes the afternoon heat off summer plants.
• Strawberries, which share the same shallow, frequent watering and low mulched bed.

Keep apart

• Celery, which shares sclerotinia rot, the fungus that collapses both from the base.
• Globe artichoke, endive and chicory, which host the same downy mildew.
• Sowthistle weeds, which harbour the aphid that carries lettuce necrotic yellows.

Harvesting Leaves

Pick loose-leaf types from four to six weeks, once leaves reach about 10 cm. Hearting types take 8 to 12 weeks and are ready when the heart feels firm.

• Pick in the morning, when the leaves are full of water.
• Take the outer leaves and leave the centre growing; the plant keeps producing for weeks.
• Cut a hearting lettuce 2.5 cm above the soil; the stump often resprouts a smaller second crop.
• Pick before the centre rises into a stalk, since bitterness follows the flower.
• Cut a crisphead while the head still gives under moderate pressure; a hard head is past its best.

Lettuce keeps best just above 0°C in the crisper. A crisphead lasts about two weeks, and dry loose leaves in a sealed bag up to four. Keep it away from apples, bananas and tomatoes, whose ethylene spots the leaves brown. Eat it fresh, in salads, sandwiches and wraps.

Common problems

Bolting. The centre rises into a flower stalk and every leaf turns bitter; heat, long days, dry soil and overgrown punnet seedlings all trigger it. See Three mistakes for water and variety, and shade summer plants from midday.

Tipburn. Brown edges on the youngest leaves and inside hearts. Calcium travels only in the water a leaf transpires, so hot days, uneven watering and soft fast growth starve new leaves, not low soil calcium. Keep moisture even and skip extra nitrogen.

Rotting and wilting in humid weather. Outer leaves slime at the base after warm rain or evening sprinklers. Water at soil level (see Care by growth stage), space plants for airflow, and keep mulch off the stems.

Damping off. Wet, crowded punnets invite it; sow thinly in fresh mix and water less. Read more

Seedlings pecked or scratched out. Birds pull seedlings and scratch mulch across rows; net at sowing. Read more

Pests and diseases

Snails matter most, and the two aphid problems are worth telling apart.

Common garden snail (Cornu aspersum) and grey field slug (Deroceras reticulatum). Both shred seedlings overnight and hide inside hearts by day. Hunt by torch after rain, set beer traps, and use an iron-based snail bait around new sowings. Read more

Currant lettuce aphid (Nasonovia ribisnigri). Scattered rather than crowded, it feeds on the youngest leaves, inside the hearts of iceberg types and deep in the rosette of open types. Spray insecticidal soap on open types, wash picked leaves well, and clear old plants. Read more on aphids

Lettuce necrotic yellows, carried by sowthistle aphid (Hyperomyzus lactucae). Leaf veins brown, inner leaves die and the plant sits yellow, stunted and twisted. The aphid lives on sowthistle, not lettuce, and infects while probing. It does not spread from lettuce to lettuce, so pull sowthistle in and around the patch.

Cutworms (Agrotis species). Hairless larvae up to 50 mm long sever seedlings at ground level at night and curl into a C when picked up. Scratch the soil around a felled seedling, collar seedlings with a cardboard ring, and weed the bed three to four weeks before sowing. Read more

Downy mildew (Bremia lactucae). Yellow angular patches on the older leaves with white fluff beneath, in cool, damp weather. Leaves need only 3 to 4 hours of wetness to infect. Space plants, keep leaves dry overnight (see Care by growth stage), remove affected leaves, and rest that bed from lettuce for two to three years. Read more

Sclerotinia rot (Sclerotinia sclerotiorum and Sclerotinia minor). The plant wilts and collapses from a rotted base covered in white cottony mould, with black resting bodies that survive in soil for years. Bin the whole plant with the soil around it, keep mulch off the stems, and rotate the bed.

Prevention first

• Sow little and often, so a lost row costs a fortnight, not a season.
• Keep the bed weeded, since lettuce seedlings compete poorly with weeds, and weeds hold the damp that mildew needs.
• Check hearts and leaf undersides every few days, since the first aphids and mildew spots are the ones worth catching.
• Pull sowthistle and remove spent plants, roots and all, rather than leaving them to rot in the bed.

Tips

1. For summer, sow heat-tolerant types such as 'Australian Yellow', 'Buttercrunch' and 'Lolla Rossa'; for winter, cos types, which hold up well in cool districts.
2. In Hobart and other cool gardens, quick lettuces planted in autumn between pea trellises crop into winter before the peas need the space.
3. Replant the strongest thinnings into a spare row, moved small and in the cool of the day, for a second crop behind the first.