Start Early, But Not Too Early

Tomatoes are warmth lovers, and a British summer rarely delivers the long, steady heat they would enjoy in their native South America. Direct sowing outdoors is a gamble that only pays off in the mildest corners of the country. The reliable approach is to sow indoors under cover, give the seedlings a protected start, and only move them outside once the risk of frost has genuinely passed.

Timing matters more than most gardeners expect. Sow too early and you will be nursing leggy, pale plants through April, struggling to find them enough light on a windowsill. Sow too late and the first trusses will not have time to ripen before September's cool nights arrive.

• Heated propagator or warm windowsill: sow from late February to mid-March.
• Unheated greenhouse or cold frame: early to mid-March.
• Plants destined for outdoor growing: late March to mid-April, so they go out at four to six weeks old rather than eight.

Choose varieties suited to a shorter season. Gardener's Delight, Moneymaker, Alicante and Sungold all crop well outdoors in most years, while Tumbling Tom and other bush types perform admirably in hanging baskets and patio pots where warmth collects.

Sowing Under Cover

Use fresh seed compost rather than last year's leftovers, which may have lost structure and nutrients. Fill a nine-centimetre pot or a module tray, firm gently, and water before sowing so you are not disturbing the seeds afterwards. Sow about 1.5cm deep, cover, and label with the variety and date — memory is a poor record keeper.

Tomato seeds germinate best at 18–21°C. A propagator makes this easy, but an airing cupboard or a warm kitchen windowsill works just as well. Expect seedlings in seven to fourteen days. The moment the first green loop appears, move the tray into the brightest light you have. A windowsill is fine, but turn the tray daily so the stems do not lean permanently towards the glass.

When the seedlings have their first pair of true leaves, prick them out into individual nine-centimetre pots. Bury each stem up to the seed leaves — tomatoes produce roots along buried stems, which builds a sturdier plant.

Potting On as Roots Fill the Trays

Watch for roots appearing through the drainage holes. That is your cue to pot on, not a moment later. Move plants into a slightly larger pot each time — 12cm, then 15cm, then the final container or grow bag — rather than jumping straight to a huge pot. Oversized pots of wet compost sit cold and sour, and young roots rot in them.

Keep the plants growing steadily rather than forcing them. Liquid feed is unnecessary at first because the compost holds enough nutrients, but after four to six weeks it will be exhausted. Switch to a balanced feed, then to a high-potash tomato feed once the first flowers open.

If you are growing under glass, give plants plenty of ventilation on sunny days. Damp, still air encourages mould and weak growth.

Hardening Off and Moving Out

This is where many crops are lost. A plant raised indoors has soft leaves and no tolerance for wind, cold or direct sun. Move it straight outside and it will check, scorch or sulk for weeks.

Harden plants off over seven to ten days, starting with a couple of hours in a sheltered, lightly shaded spot and building up gradually to a full day and then overnight. Bring them in if frost is forecast. As a rough guide, the last frost falls in late April on the south coast, mid to late May across the Midlands and Wales, and late May or early June in northern England and Scotland. Local knowledge beats any calendar.

Choose a sunny, sheltered final position: against a south-facing wall or fence is ideal, since bricks and timber release warmth overnight. Allow 45–60cm between cordon plants. Grow bags are convenient but dry out fast; a 10–15 litre pot or ring culture gives roots more room and more consistent moisture.

Watering, Feeding and Training

Consistency is everything with tomatoes. Little and often beats a weekly soaking. Container-grown plants may need water daily in midsummer, and twice on hot days. Erratic watering is the usual cause of blossom end rot and split fruit, because it disrupts the plant's uptake of calcium — the answer is steady moisture, not a calcium feed.

• Cordon varieties: pinch out the side shoots that appear in the leaf axils every week, and stop the main stem once four to six trusses have set.
• Bush varieties: leave them to branch naturally, but support heavy trusses with a short cane.
• Feeding: high-potash tomato feed weekly from the moment the first truss sets.
• Yellowing between leaf veins: a sign of magnesium shortage, often eased by a dilute Epsom salt spray.

Keeping Plants Healthy Through the Season

Outdoor tomatoes in wetter parts of the country face blight, especially from July onwards. Grow under cover if you can. Otherwise, remove the lowest leaves to improve airflow, water the soil rather than the foliage, and avoid crowding. If blight strikes, strip affected leaves promptly and ripen what fruit you can indoors.

Under glass, watch for whitefly, aphids and red spider mite. Good ventilation and regular inspection keep most problems manageable. By late August, pinch out the growing tip of cordon plants to push energy into ripening the fruit already set rather than producing more flowers that will never mature.

Green fruit at the end of the season is not a failure. Pick it before the first frost, bring it indoors, and lay it in a single layer somewhere cool and light, or in a paper bag with a ripe banana. Most of it will colour up within a fortnight — and a home-grown tomato in October is a fine reward for a spring's patience.