How to grow lettuce

In the week before you sow the nursery, pick a stretch where the daytime average stays below about 25°C — the cool season, or the cooler highlands. Lettuce is happiest between 15 and 20°C.

Count backwards from that cool weather. The crop needs about 3–4 weeks in the nursery, then roughly 4 to 10 weeks in the field depending on type — loose-leaf is quicker (about 4–6 weeks after transplanting) and head types slower (about 8–10 weeks) — so make sure that whole run lands in the cool and doesn't slide into the hot season.

If your area is warm, plan to sow in the coolest part of the year, or grow only in a shaded, well-watered spot. Loose-leaf types take heat best; save tight crisphead (iceberg) for the coolest times.

Don't sow so the plants would heat up as they fill out — heat while they are heading is exactly what turns lettuce bitter and makes it bolt (run to a flower-stalk instead of staying leafy).

On sowing day, fill a seed-tray or a fine, level nursery bed with moist, well-drained seed mix or fine soil. Water it first so it is damp all the way through before you sow.

Sow very shallow — no deeper than your fingernail (about ½–1 cm) — and barely cover it, because light helps lettuce seed sprout. The seed is as fine as sand, so sow it thinly and evenly.

Keep the seedbed cool (about 18–21°C) and constantly moist. In warm weather, sow in the cool of late afternoon, shade the bed, and water to cool the soil — lettuce seed refuses to sprout in hot soil (its 'heat-block').

If your weather is warm and the seed won't come up, ask your supplier for primed seed — seed the supplier has part-woken so it sprouts faster and copes better with warmth.

Water with a fine rose or a soft sprinkle so you don't wash the seed out. Expect sprouts in a few days, and seedlings ready to move in 3–4 weeks, when each has 1 to 3 true leaves (the proper leaves that come after the first pair of rounded seed-leaves).

Starting about 5–7 days before transplanting, give the seedlings a little more sun and wind each day — move the trays out, or open the shade, for a couple more hours at a time.

Ease back the watering a little so the plants firm up and toughen — but never let them wilt hard.

By transplanting day they should stand up to full outdoor sun without flopping. Water them well the evening before you lift them, so they move with damp roots.

Do this about 1–2 weeks before you transplant, so the bed has time to settle before the seedlings arrive.

Clear the ground of old crop residue and weeds, then dig or till it deep and loose — a rough, cloddy bed chokes lettuce's shallow, fine roots.

Work in well-rotted compost or manure — dark, crumbly, no strong smell — generously, since lettuce is a hungry crop for such a short life. Fresh, strawy manure burns the young roots, so only use it well rotted.

Apply the basal fertiliser your recommendation gives — lettuce wants phosphorus for the roots and potassium and calcium for firm, crisp leaves, not just nitrogen.

On heavy or wet soil, raise the bed into ridges or beds so water never stands around the shallow roots — waterlogging rots them fast.

Rake the surface level and fine so water spreads evenly and the young transplants meet no clods.

Buy compact, dark-green seedlings with 1 to 3 true leaves — not tall, pale or leggy ones, and not ones that look stressed or hardened too hard.

Check each one: no mottled, puckered leaves (a sign of lettuce mosaic virus), no aphids in the heart, and no wilting.

Ask whether the seedlings were raised in the cool — ones raised through heat may already be stressed toward bolting once they're in the field.

Transplant them within a day or two of buying, keeping them shaded and moist until you do — lettuce transplants dry out and check fast.

Transplant on the day the seedlings are ready, in the cool of the day — early morning or late afternoon — never in hot sun.

Set the seedlings at spacing: head types about 25–35 cm apart in the row (roughly one-and-a-half hand-spans) and 30–45 cm between rows (about two hand-spans). Loose-leaf types go a little closer. Put one seedling per station.

Plant each one so the lowest leaves sit just above the soil — don't bury the growing centre (the heart the new leaves come from), or it rots. Firm the soil gently around the roots so there are no air pockets.

Water in straight away, right at the base, so the roots meet wet soil and never dry. If a plant flops on the first day, shade it and water it again.

Growing from direct-sown seed instead? Don't transplant — thin the young plants to the same spacing, keeping the single strongest seedling at each station.

Water every 2–3 days right through the first fortnight after transplanting — more often in heat, or on sandy soil that dries fast.

Keep the top of the soil constantly damp — never bone-dry, and never waterlogged (soggy soil rots the shallow roots).

Check with a finger: if the top few centimetres (about a finger-joint down) are dry, water. Push in near a plant — you want it damp at root depth.

Water at the base, in the morning where you can, so the leaves dry through the day — wet leaves overnight invite disease.

Weed by hand or a light hoe within the first 2–3 weeks after transplanting, while the weeds are still small.

Hoe shallowly and keep the blade away from the plants — lettuce roots run just under the surface and are easily cut.

Pull the weeds right next to each plant by hand, so you don't nick the roots or bruise the leaves.

Clear weeds from between the rows too, so air moves through the crop and the leaves dry — this alone cuts disease.

From a few days after transplanting, walk the bed twice a week and look closely at a few plants in each part — the leaf undersides and the growing centre, not just the tops.

Cutworms: look for young plants cut clean off at the soil line, worst overnight. Scratch the soil beside a felled plant to find the fat, greasy, grey caterpillar curled into a C.

Slugs and snails: look for ragged holes chewed in the leaves and silvery slime-trails, worst after rain and at night.

Aphids: look for clusters of tiny soft green or grey insects on the leaf undersides and in the heart.

Count how many plants show fresh damage and note where. If seedlings are being felled or holed and the gaps are spreading, act now — bait for slugs and cutworms in the evening, and rub out or wash off the first aphid colonies before they build up.

Keep any slug or cutworm bait away from children, poultry and pets — it is made to be tempting to eat and is poisonous to them too; scatter it thinly along the row, not in heaps, and store the rest locked away.

If a pest is spreading fast → treat that evening and re-check in 2–3 days. If it's only old, dried damage with no pest → leave it and keep watching.

Starting about 2 weeks after transplanting, feed small amounts of nitrogen every 10–14 days through the growing stretch — the amount your recommendation gives for your bed. Keep it light; more is not better with lettuce.

Band it in a thin line to the side of the row and water it in — never scatter it over the plants.

Keep fertiliser off the leaves — grains sitting on damp leaves scorch them, and these leaves will be eaten raw. Brush off anything that lands on a plant.

Lettuce also wants potassium for firm, crisp leaves — if your recommendation is a compound (balanced) feed rather than straight nitrogen, it carries that too. Follow the amount it gives; don't add extra.

Stop feeding nitrogen as the heads start to firm. Late nitrogen swells soft, nitrate-heavy leaves and drives tipburn — it does not build a better head.

Hold the moisture dead-steady while you feed: calcium (the nutrient that keeps the inner leaves from scorching) only reaches the young heart-leaves when the water is even — that steadiness is what actually holds tipburn off.

From about 2 weeks after transplanting right up to harvest, water every 2–3 days to keep the soil evenly damp at all times — no wet-then-dry swings. On sandy soil and in heat, water more often.

Aim for the same amount on the same rhythm — steadiness matters more than an occasional big soak.

Water at the base, in the morning, so the leaves dry through the day — this keeps downy mildew down while it keeps the moisture even.

In hot spells, a little extra water and light shade cools the crop and helps hold off bolting and bitterness.

Through the whole growing stretch, walk the crop twice a week and check the leaf undersides and the heart of each plant, across every part of the bed.

Aphids: look for clusters of tiny soft green or grey insects on the undersides and in the centre. Treat the first colonies now — before the heads close, because once they're sealed inside, the head is ruined.

Downy mildew: look for pale yellow angular patches on the upper leaf (boxed in by the veins) with a white or grey fuzzy mould underneath them. It strikes in cool, damp, leaf-wet weather — act on the first patches, and pick off and remove badly-hit lower leaves.

Slugs and snails: ragged holes and silvery slime-trails, worst after rain — bait or hand-pick in the evening.

Mottled light-and-dark-green patches with puckered, distorted small leaves is lettuce mosaic virus — there is no cure. Pull out and remove affected plants, control the aphids that spread it, and use clean seed next time.

Remember: brown scorched inner-leaf edges are tipburn, not a pest — don't spray for that; steady the water and ease off nitrogen instead.

Head types (butterhead, cos, crisphead): gently squeeze the head — it's ready when it feels firm and well-filled, not soft and open. Cut these from about 8–10 weeks after transplanting.

Loose-leaf: it's ready as soon as the leaves reach a usable size — pick from about 4–6 weeks after transplanting, before they turn bitter. You don't wait for a head to form.

Look hard at the centre of each plant: a heart that is stiffening and stretching upward, or a seed-stalk starting to rise, means bolting — cut that plant today.

Taste a leaf if you're unsure — any bitterness means cut now; bitterness only gets worse.

If a plant isn't ready yet → leave it, keep the water steady, and check again in a few days. But if it's starting to bolt → cut it immediately, ready or not — quality collapses from here, and waiting loses everything.

Harvest in the early morning while it's cool — never in the heat of the day, when the leaves are soft and wilt fast.

Head types: cut the whole head through the stem at the base with a clean, sharp knife, and strip off the loose, dirty or damaged outer leaves.

Loose-leaf: either pick the outer leaves a few at a time (leaving the centre to keep growing) or cut the whole rosette — the low circle of leaves — at the base.

Cut before any bolting: go through the bed every 5–7 days and take each plant as it comes ready — a bolting plant is worthless, so never leave it standing.

Handle the leaves gently — they bruise easily — and get them straight into the shade, never left lying in the sun.

Get the cut lettuce out of the sun and into the shade immediately — never let it sit in the field heat.

Cool it within hours, not at day's end: dunk or spray it in clean, cold water, or hold it somewhere cool — the faster the field heat comes out, the longer it lasts.

Trim off damaged, dirty and outer leaves, and wash in clean water — lettuce is eaten raw, so clean water is a safety matter, not just for looks.

Let the surface water drain, then keep the lettuce cool, shaded and damp (a cool room, a damp cloth, the coolest store you have) right up to market.

Move it to sale quickly — even well-cooled, lettuce does not keep long.