Lettuce 'Baby Cos' Organic: Sowing to Harvest Guide
By The Diggers Club - Australia's No.1 Gardening Club | Published: 2026-11-03
Category: How-to Guides
Grow crisp, sweet baby cos lettuce from seed with this step-by-step guide, covering sowing times, thinning, watering and when to harvest for the best Caesar salads.
Quick answer
Sow lettuce 'Baby Cos' (Organic) seed thinly, 5–10 mm deep, in moisture-retentive soil during the cooler months, then thin seedlings to about 20 cm apart and keep the bed consistently damp. Harvest the whole head at around 9 weeks, or pick outer leaves earlier for cut-and-come-again salads.
Why baby cos suits small gardens and pots
Baby cos forms compact, upright heads rather than sprawling, so it fits into narrow beds, balcony pots and interplanted gaps. That same tight habit means airflow around the base can be poor if you crowd plants, which is why thinning matters more than it does for loose-leaf types.
The trade-off is that baby cos has a smaller root run than full-size cos. In pots, use a container at least 20 cm deep and water more often, because a shallow pot dries out faster than open ground.
Timing lettuce seed sowing in Australia
Lettuce germinates poorly when soil is hot, so avoid sowing in the peak of summer in warm zones. In most Australian climates, the reliable windows are early spring and autumn; in frost-free areas, autumn and winter sowings often give the crispest heads.
If you garden in the tropics, treat lettuce as a dry-season crop and sow where it receives afternoon shade. In cool highlands, a spring sowing after the last frost works well, but heads may bolt quickly once hot weather arrives.
Soil, water and the bolting risk
Cos lettuce is shallow-rooted, so the top 15 cm of soil does the work. Dig in compost before sowing and keep the surface from crusting. A light mulch helps hold moisture but keep it a few centimetres clear of the stems to reduce rot.
The main disappointment with baby cos is bolting — running to seed before forming a heart. It is triggered by heat and by drying out. Consistent watering and choosing the right sowing window do more for head quality than heavy feeding, which can produce soft, floppy leaves.
Step-by-step: sowing to harvest
- Prepare a fine seedbed: Clear weeds and loosen the top 10–15 cm of soil, then firm it lightly and water before sowing. Lettuce seed is small and needs good seed-to-soil contact. Sow into damp, not soaked, soil so the seed does not rot before germinating.
- Sow thinly at the right depth: Sow seed 5–10 mm deep in rows about 20 cm apart, or scatter thinly in a pot. Cover lightly with soil or seed-raising mix and mist the surface. A common mistake is burying seed too deep; if you cannot just cover it, you have gone too far.
- Keep moisture steady until germination: Mist daily or as needed to keep the surface moist but not waterlogged. Germination is usually quick in mild weather, slower in cold soil. Check under pots and mulch for slugs and snails, which graze new seedlings overnight.
- Thin seedlings early: When seedlings have two or three true leaves, thin to about 20 cm apart for full heads, or closer if you plan to harvest young leaves. Snip extras at soil level rather than pulling, which disturbs neighbours. Crowded baby cos tends to bolt or rot at the base; thin before the leaves touch.
- Water and feed lightly: Water deeply once or twice a week, more often in pots or hot weather. Apply a weak liquid feed every few weeks only if leaves look pale; too much nitrogen makes soft growth. Aim for even moisture — alternate drying and soaking stresses the plant and encourages bolting.
- Harvest at the right stage: For whole heads, wait until the centre is firm and the head feels solid, around 9 weeks from sowing. For cut-and-come-again, pick outer leaves from about 6–7 weeks, leaving the crown to regrow. Harvest in the cool of morning and plunge stems into cold water to keep leaves crisp.
Product facts
- Lettuce 'Baby Cos' (Organic): Lettuce 'Baby Cos' (Organic) is a sweet, crunchy baby cos suited to gardens of all sizes, including pots, with a harvest window of about 9 weeks. That short, predictable timing makes it easy to plan successive sowings for a steady supply rather than one glut.
Lettuce 'Baby Cos' (Organic)
