Starting seeds indoors is the skill that unlocks the whole gardening year: it gives tender crops a head start on spring, lets you grow varieties no garden centre stocks, and costs a fraction of buying plants. But it is also where most beginners go wrong — leggy, pale seedlings that collapse are almost always a light problem, not a skill problem.
This guide covers what to start indoors and when, the simple light-and-warmth setup that works on any windowsill, hardening off, and the classic mistakes to avoid. Written for Central and Western Europe, no special equipment assumed.
| Question | Simple answer |
|---|---|
| What to start indoors? | Tender crops: tomatoes, peppers, cucumbers, courgettes, basil |
| What to sow direct? | Root veg, peas, beans — they hate transplanting |
| When to start? | Count back from planting-out date on the packet |
| Light needed? | Maximum — a bright south/west windowsill or a grow light |
| Heat needed? | Room temperature for most; no heat mat required |
| Hardening off? | Yes — 7–10 days of gradually increasing outdoor time |
Step 1: Know what to start indoors — and what not to
Start indoors the crops that need a long, warm season: tomatoes, peppers, cucumbers, courgettes, basil and leeks (for their long season). These gain weeks from an indoor start that direct sowing cannot give them.
Sow directly outdoors instead: carrots, parsnips, peas, beans, spinach and chard — their roots resent disturbance, and they germinate fine in cool spring soil. Starting these indoors is the most common beginner mistake: more work for worse plants.
Step 2: Time it from the packet — not from impatience
The number one seed-starting error is starting too early. A tomato sown in February on a dark windowsill becomes a leggy monster by April; one sown in late March is stocky and overtakes it within weeks. Read the packet: it gives weeks-before-last-frost, and it is right.
Typical Central Europe indoor-sowing times: tomatoes and peppers late March, cucumbers and courgettes late April (they grow fast — 3–4 weeks indoors is plenty), leeks February–March. When in doubt, sow later rather than earlier — late sowings in good light catch up astonishingly fast.
Step 3: Give them maximum light — this is everything
Light is 90% of seed-starting success. Seedlings stretch toward light, and weak light means tall, pale, floppy stems that never recover. Put trays on your brightest windowsill — south or west facing — right against the glass, and turn trays daily so seedlings grow straight.
If your windowsills are dark, a simple LED grow light (kept 10–15 cm above the seedlings, on 14–16 hours a day) transforms results for very little money. It is the single best investment a seed-starting beginner can make. Without enough light, everything else — compost, heat, feeding — barely matters.
A cheap timer plug makes the light schedule effortless — set it for 6am to 10pm and forget it. Keep the light close: seedlings stretch toward distant light, so raise the lamp as plants grow, always keeping that 10–15 cm gap. The difference between windowsill-only and supplemented seedlings is visible within a week: stocky, deep-green plants versus pale, leaning ones.
Step 4: Keep it simple — warmth, moisture, air
You do not need special equipment. Sow into multipurpose compost in trays, modules or small pots (modules beat trays — less root disturbance at transplanting). Cover seeds to the depth the packet says (roughly twice the seed's width), water gently, and keep at normal room temperature — 18–22°C suits almost everything. No heat mat needed for beginners.
Keep compost moist but never soggy — a spray bottle for the first days, then careful watering from below once seedlings are up. Covering trays with a clear lid or cling film holds humidity for germination; remove the cover the moment seedlings emerge, or damping-off fungus will fell them. A little air movement (an open window nearby, not a gale) grows sturdier stems.
Label everything the moment you sow — variety and date. Every gardener has a tray of mystery seedlings; a permanent marker and plastic labels cost almost nothing and save real confusion later. Note sowing dates in a notebook too: next year you will know exactly what worked, and your timing will get sharper every season.
Step 5: Pot on at the right moment
Seedlings in trays need pricking out (moving to individual pots) once they have their first true leaves — the second pair, after the initial seed leaves. Handle by a leaf, never the stem (a crushed stem kills; a torn leaf regrows). Pot into 9 cm pots of fresh compost, water in, and return to maximum light.
Do not pot on too late: root-bound seedlings stall and never fully recover. But do not rush either — moving tiny seedlings with only seed leaves usually kills more than it saves. First true leaves is the signal. Tomatoes can be potted deeper than they were growing (they root from the buried stem); most others go in at the same depth.
Step 6: Harden off — never skip this
Indoor seedlings moved straight outside suffer transplant shock: sunburn, wind damage, cold nights. Hardening off — 7–10 days of gradually increasing outdoor exposure — prevents it. Start with a few sheltered hours in daytime, bring in at night; lengthen the time and exposure daily until they stay out overnight.
Only plant out after the last frost for tender crops (tomatoes, peppers, cucumbers, courgettes, beans) — check your local frost dates, typically mid-May in Central Europe. Water well at planting and protect with fleece if a late cold snap threatens. Our first vegetable garden guide maps the whole spring sequence.
A cold frame or even a sheltered corner against a south-facing wall makes hardening off far easier — it buffers wind and catches daytime warmth while exposing plants to real outdoor conditions. No cold frame? A cardboard box laid on its side as a windbreak works surprisingly well for the first few days. The goal is gradual exposure, not toughness training: stressed seedlings stall for weeks.
Troubleshooting: seed-starting problems
Tall, pale, floppy seedlings leaning toward the window: Not enough light — the classic. Move to the brightest spot immediately, turn daily, and consider a grow light. Badly leggy seedlings rarely recover; it is often faster to re-sow than to nurse them.
Seedlings keeling over at soil level: Damping off — a fungus that strikes in still, damp, airless conditions. Remove covers at germination, water from below, improve air circulation, and sow thinly. Affected seedlings cannot be saved; start fresh in clean trays.
Seeds not germinating at all: Old seed, sown too deep, or too cold. Check packet dates (parsnip and parsnip-family seed dies fast), sow at the right depth, and keep at room temperature — a cold windowsill in February is too chilly for heat-lovers like peppers.
Seedlings stalled, purple-tinged, not growing: Too cold, or starved in tiny cells. Move somewhere warmer, pot on into fresh compost, and be patient — growth resumes when warmth returns. A very weak liquid feed helps once true leaves are out.
What to do this October
October is not seed-starting season — but it is seed-starting preparation season. Clean and store trays, modules and pots now (disease overwinters in dirty trays — see the October checklist), check what compost and seeds you have left, and order next spring's seeds while choice is best.
The one thing you can sow indoors in October: microgreens and herbs on the windowsill — cress, mustard, basil and parsley grow happily in winter light and keep your hand in until spring. See the full December checklist for winter indoor growing ideas.
Frequently asked questions
Do I need a heated propagator?
No — normal room temperature germinates almost everything a beginner grows. Heat mats help peppers and chillies germinate faster, but they are a luxury, not a necessity. Light matters far more than heat.
Can I reuse last year's compost for sowing?
Better not — old compost may harbour damping-off fungi and is depleted of nutrients. Use fresh multipurpose compost for sowing; save the old stuff for mulching beds.
Why do garden-centre plants look better than mine?
Professional light, heat and feeding — and they sow at exactly the right moment. Yours will catch up: a stocky home-grown plant transplanted at the right time outperforms a leggy early one every time.
Is direct sowing really worse for tomatoes?
In Central and Western Europe, yes — the season is too short and cool for direct-sown tomatoes to ripen reliably. Indoor starting is not optional fuss for tender crops; it is what makes them possible at all.
Related guides
- How to Grow Tomatoes at Home: Beginner's Guide — the number one indoor-started crop
- Your First Vegetable Garden: A Complete Beginner's Guide — plan your sowing year
- How to Grow Herbs at Home: A Beginner's Guide — easy windowsill wins while you learn
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