Lesson 3
Sowing, potting on, and the timeline
Sow indoors in late March or early April. Any earlier and the plants outgrow their space before it is warm enough to go outside. Use fresh seed compost, sow two seeds per 7 cm pot, cover lightly, and keep at 18–21°C. Germination takes 7–10 days. The moment the first true leaves appear — the serrated ones, not the smooth seed leaves — move the pots to the brightest spot you have, ideally a south-facing windowsill.
Pot on when roots reach the edge of the pot, usually 3–4 weeks after sowing. Go to 1-litre pots, then 3-litre, then final 30-litre containers. Each time, bury the stem up to the lowest leaves — tomatoes root from the stem and a deep plant is a strong plant. Use a peat-free multipurpose compost mixed half-and-half with good garden compost or well-rotted manure. Add a handful of pelleted chicken manure or slow-release tomato fertiliser at the final potting.
Harden off for a full week in mid-May, bringing pots outside during the day and in at night. Plant into final containers only when night temperatures stay above 10°C — usually late May or early June. Earlier than that and growth stalls. Heritage varieties do not recover well from a cold check.
Numbers that matter
- Sowing: late March to early April indoors
- Germination: 7–10 days at 18–21°C
- First potting on: 3–4 weeks after sowing
- Final planting out: late May when nights stay above 10°C
- First fruit: 75–95 days after planting out, depending on variety
The potting-on sequence
- 1.Sow in 7 cm pots late March; germinate at 18–21°C.
- 2.Pot on to 1-litre pots when first true leaves are well-developed.
- 3.Move to 3-litre pots 2–3 weeks later; begin weekly liquid feed.
- 4.Harden off fully in mid-May; acclimatise over 7 days.
- 5.Plant into final 30-litre pots late May; bury stem deep.
- 6.Stake immediately with 180 cm cane or spiral support.
Always pot on before the roots circle — once they spiral, the plant remembers and never grows as vigorously.