How to Grow Tomatoes from Seed (Solanum lycopersicum)

Tomatoes are the reason most people start a vegetable garden from seed in the first place — and the reason so many end up disappointed with pale, watery supermarket fruit next to what they grew themselves. Two of our most popular autumn guides, ripening green tomatoes and saving your own tomato seed, both assume you already have a plant. This is the guide that comes before those: how to sow, grow and train Solanum lycopersicum from a packet of seed to a plant carrying its first ripe truss.

With more than seventy varieties in our range — from tiny Tiny Tim cherries to two-fisted Supersteak beefsteaks — the real skill is not sowing the seed, which is easy, but choosing the right growth habit for your space and keeping the plant fed, watered and trained through a long season.

• Botanical name Solanum lycopersicum — a tender perennial grown as an annual
• Sow indoors February–March for greenhouse cordons · March–April for outdoor and bush types · into June for hanging baskets
• Germination 18–21 °C · 7–14 days
• Harvest July–October, depending on variety and sowing date

Cordon, bush or dwarf — choose the habit before the variety

Every tomato in the catalogue falls into one of three growth habits, and it matters more than flavour or colour when deciding what to grow.

• Cordon (vine, indeterminate) — keeps growing upwards all summer, needs a cane or string and weekly side-shooting, but gives the biggest crop and widest choice: beefsteaks like Marmande and Brandywine, plum types such as San Marzano and Roma VF, and most cherries. Best under glass or against a warm wall.
• Bush (determinate) — stops itself at a set height, needs no side-shooting, and crops over a shorter, more concentrated period. Varieties such as Maja suit an open, unheated spot.
• Dwarf, patio and hanging basket types — small, self-branching plants for pots rather than beds; our hanging basket tomatoes such as Koralik trail neatly over the rim and need no support.

A small garden or a first attempt is usually happier with a bush or patio variety; a greenhouse and a taste for beefsteaks justifies the extra work of a cordon.

When to sow

Tomatoes need warmth from seed to harvest, so the sowing date is a question of how much season you can offer. Nearly every variety in our range is tagged from February through May, with a few pot and basket types stretching into June and July:

• February: greenhouse cordons and beefsteaks, started with a heated propagator for a long season under glass — see the vegetable sowing calendar and the February sowing range.
• March: the main sowing month for most varieties, whether bound for glass or outdoors — the March sowing collection.
• April: a safe, slightly later sowing for outdoor bush and patio types, ready to plant out once frost risk passes — the April sowing range.
• May–June: a last, quick option for dwarf and hanging varieties such as Koralik.

Sowing earlier than February rarely pays off: without a grow light, seedlings on a dim windowsill grow leggy and are overtaken within weeks by a well-lit March sowing (see the 10-hour daylight rule).

How to sow tomatoes, step by step

1. Sow shallow in warm compost One or two seeds per pot or module, 1 cm deep, lightly covered.
2. Keep at 18–21 °C A propagator lid or warm windowsill germinates in about a week; below 15 °C seed can sit a month. See how to germinate seeds.
3. Full light the moment they emerge Lid off at once, brightest spot available — warmth without light causes leggy seedlings.
4. Pot on deep At the first true leaves, move to a 9 cm pot, planted deeper than it was sitting. Unlike peppers, tomato stems root wherever they touch compost.
5. Pot on again, then plant out A 1–2 litre pot as roots fill it, then a final growbag, border or basket once nights stay above 10 °C and plants are hardened off.

Training, feeding and watering

A cordon needs a job every week: tie the main stem loosely to a cane or twine, and pinch out the side shoots in the leaf joints while small enough to nip out (plant supports and trellising). Left a week, a side shoot becomes a second stem and crowds the plant. Bush and dwarf types need none of this — just a light stake if they flop.

Once the first truss sets fruit, switch to a high-potash tomato feed weekly (feeding and fertilising); too much nitrogen grows leaves, not fruit. Watering matters even more: keep compost evenly moist rather than alternating dry and sodden — a sudden soak after a dry spell is the main cause of split skins and blossom end rot, the sunken black patch caused by a stalled calcium supply. Consistency is the fix. Outdoors, stop a cordon by pinching out the growing tip after six or seven trusses; under glass, ten or more is realistic.

Pests, disease and harvest

Check leaves for aphids and whitefly through the season, especially under glass (common garden pests). Watch for blight — brown blotches that spread fast in warm, wet weather (plant diseases guide); good airflow and watering the soil rather than the leaves both help.

Pick fruit as it fully colours, twisting gently at the calyx. Cropping runs from July for early cherries under glass to October outdoors. When frost threatens with fruit still green, our guide to ripening green tomatoes indoors covers it, and once you've picked your best fruit of the year, saving tomato seed walks through the short ferment that keeps it viable for years — on open-pollinated varieties only, not F1s (heirloom vs F1 vs organic seeds).

Common mistakes

• Sowing too early without a grow light. A dim winter windowsill gives a weak plant that a well-timed March sowing soon overtakes.
• Leaving side shoots to grow. Left a week, one becomes a second stem and crowds the plant.
• Irregular watering. Drying out, then soaking, is the main cause of split fruit and blossom end rot.
• Feeding too much nitrogen. Lush leaves, few flowers — switch to a potash feed once fruit sets.
• Planting out too early. One cold night below 5 °C checks a plant for weeks.

Frequently asked questions

Can I still sow tomato seed in September?
Not for a crop — too little light and warmth left before winter. For unripe fruit on an existing plant, see ripening green tomatoes; for what can still go in now, see what to sow in October.

Cordon or bush — which is easier for a beginner?
Bush and dwarf types are more forgiving: no side-shooting, no staking beyond a light cane. A cordon takes weekly attention but gives a bigger crop over a longer season.

Why is my tomato fruit splitting or developing blossom end rot?
Both usually trace to inconsistent watering — a dry spell followed by a heavy soak swells fruit faster than the skin can stretch and disrupts calcium uptake. Water little and often.

Do I need a greenhouse to grow tomatoes?
No. Bush and patio varieties crop reliably outdoors from June in a sunny, sheltered spot, or in a growbag or large container (container gardening from seed). A greenhouse mainly extends the season, which matters most for beefsteak and plum types.

Tomatoes reward patience with the seed tray and a little weekly discipline once growing — the rest is warmth, water and time. For the fundamentals behind every crop, see our beginner's guide to growing vegetables from seed, and if this year's harvest is heading into store too, our new guide to storing apples & pears for winter covers the other end of the kitchen garden. Browse the full tomato collection, the cherry and snack types, our organic tomato range, the wider vegetable seed collection and our growing guides library.