Seedlings, step by step

1. When to sow

The sowing date isn't printed on the calendar: you count it back from the last spring frost.

1. What to raise as transplants — Tomatoes, peppers, aubergines, celery and leeks always as transplants. Cabbage and lettuce can go either way, while carrots, peas, French beans and sweetcorn are sown direct.
2. Count from the frost — The date is counted back from the last spring frost in your area. In lowland UK and Ireland that is roughly 1 May.
3. Peppers 10, tomatoes 8 — Peppers and aubergines 10 weeks before the frost, tomatoes 8, cabbage 6, cucumbers 2 weeks before.
4. Don't rush — Tomatoes sown in January have outgrown their pots by May, gone leggy and flowered indoors. Better a week late than a month early.

Why: In the UK, Ireland and most of the northern US and Canada, the season is too short to sow tomatoes, peppers and aubergines straight into the garden. So they are raised indoors for 6–12 weeks. Sowing too early is the most common mistake.

• Rough last-frost dates: lowland England, Wales and inland Ireland around 1 May, upland areas and northern Scotland late May, the mild coasts of south-west England, Wales and southern and western Ireland around 1 April.
• For upland areas add 3–4 weeks, for the mild coasts take off about 4 weeks. In the US and Canada, go by your zone and local frost data. The dates are approximate, ± 1 week.

2. Compost and containers

Seed compost is loose, fine, free of weeds and poorer than garden soil.

1. Seed compost — Bought seed compost (peat-free is widely available), or 1 part sieved garden soil and 1 part sand or perlite. Fine, no lumps.
2. Wet it the day before — Dry peat-free compost, coir and peat repel water. Squeeze a handful: it should hold together without water dripping out.
3. Containers with holes — A shallow tray for dense sowing, 4–5 cm cells for cabbage and lettuce, 8–10 cm (3–4 in) pots for tomatoes and peppers. Always holes in the bottom.
4. Label every container — Crop, variety, date. In five weeks you won't tell a hot pepper from a sweet one.

Why: A young seedling has food in the seed for its first weeks. A mix that is too rich, fresh manure or unfinished compost burns the roots.

• Pasteurising: keep moist soil under foil in the oven at about 80 °C (176 °F) for half an hour. Bought compost doesn't need pasteurising.
• Wash old containers in hot soapy water before use.

3. Sowing · Locked

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4. Light and temperature · Locked

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5. Pricking out and watering · Locked

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6. Hardening off and planting out · Locked

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