How to Grow Tomatoes – Complete Guide from Seed to Harvest

Choosing the right tomato variety

The first decision – and a meaningful one. Tomato varieties differ in growth habit, fruit size, disease resistance and suitability for different climates. The two most important categories:

For outdoor growing in cooler climates, look for varieties with blight resistance – Crimson Crush, Lizzano, Fantasio. These won't eliminate the risk entirely but give you more time before disease strikes.

When to sow tomatoes from seed

Tomatoes need a long growing season – typically 16–20 weeks from sowing to first harvest. That means starting early, indoors. The right sowing window depends on your last frost date:

• Count back 6–8 weeks from your last expected frost date
• In most of the UK and Northern Europe: sow late February to mid-March
• In the US: varies widely by region – check your local frost calendar

Sowing too early (January) produces seedlings that outgrow their space before it's safe to plant out. Sowing too late (May) means a shortened harvest season. The window matters.

How to sow tomatoes from seed

1. Fill small pots or seed trays with fresh seed compost – not multipurpose compost, which can be too coarse.
2. Sow seeds 1 cm deep, one or two per pot. If sowing in trays, space seeds 3–4 cm apart.
3. Cover with a thin layer of compost or vermiculite and water gently.
4. Cover with a propagator lid or clingfilm to retain humidity.
5. Place somewhere warm – 20–25°C is ideal. A heated propagator works best; a sunny windowsill works if temperatures are high enough.
6. Seeds germinate in 6–10 days. Remove the cover as soon as seedlings emerge and move to the brightest position available.

Pricking out and potting on

When seedlings have their first true leaves (the second pair), it's time to prick them out into individual 9 cm pots. Handle seedlings by a leaf, never the stem – a damaged leaf is replaceable, a damaged stem is not.

Tomatoes root along their stems, so when potting on, bury the stem deeper than it was before. A leggy seedling can be buried right up to its lowest leaves, converting the stem into roots and producing a shorter, sturdier plant.

Pot on again when roots reach the edge of the pot. Most tomatoes go through 9 cm → 1 litre → final position (outdoors or in a large container/grow bag).

Hardening off and transplanting

Tomato seedlings raised indoors are not ready for outdoor conditions. They need to be hardened off – gradually acclimatised to wind, temperature swings and outdoor light levels.

Start by putting plants outside in a sheltered spot for a few hours on mild days, bringing them in each night. Over 10–14 days, gradually increase the time outside and exposure to the elements. Only plant out when night temperatures stay reliably above 10°C and all frost risk has passed.

Plant spacing for outdoor tomatoes:

• Indeterminate cordon varieties: 45–60 cm apart in rows 75–90 cm apart
• Bush varieties: 45–60 cm each way
• In grow bags: no more than 2–3 plants per standard bag

Watering tomatoes correctly

Inconsistent watering is the leading cause of blossom end rot and fruit splitting in tomatoes – two problems often blamed on nutrient deficiencies or poor varieties.

The key principles:

• Water deeply and consistently. Aim to keep soil evenly moist, not waterlogged and not drying out completely between waterings.
• Water at the base, not the leaves. Wet foliage promotes blight. Use a watering can with a long spout or drip irrigation.
• Increase watering as fruits develop. Tomatoes need more water when they're sizing up – erratic watering at this stage causes fruit to split as it expands too rapidly.
• In containers, daily watering may be needed in hot weather. Check by pushing a finger 5 cm into compost – water if it's dry at that depth.

Feeding tomatoes

Tomatoes are heavy feeders. Once the first flowers appear, begin weekly feeding with a high-potassium fertiliser (labelled for tomatoes). Potassium supports fruit development and flavour; too much nitrogen at this stage produces leafy growth at the expense of fruit.

A simple schedule:

• From planting to first flower: balanced fertiliser or none (if the compost is fresh)
• From first flower onwards: weekly tomato feed (high potassium)
• Continue until late summer or until plants start to decline

Pruning indeterminate tomatoes

Indeterminate varieties produce sideshoots in every leaf axil – the junction between the main stem and a leaf. Left unpruned, each becomes a second growing stem, then a third, and so on. The result is a sprawling plant with many small fruits rather than a focused, productive plant with good-sized fruit.

Remove sideshoots when they are small – 2–5 cm – by pinching them out with your fingers. Larger sideshoots can be cut with clean scissors or a knife. Check weekly during the growing season.

In late summer (typically mid-August in the UK), stop the plant by pinching out the growing tip. This redirects energy from new growth into ripening existing fruits before the first frost.

For more detail on which shoots to remove and which to keep, see our guide to tomato suckers and training methods.

Common tomato problems and how to prevent them

• Blight (Phytophthora infestans): Brown patches on leaves and stems, rapidly spreading in warm, wet weather. Prevention: water at the base, remove lower leaves to improve airflow, choose resistant varieties. There is no cure once established – remove affected plants promptly to stop spread.
• Blossom end rot: Black, sunken patch at the base of fruit. Caused by calcium deficiency, nearly always triggered by inconsistent watering. Fix the watering schedule; calcium sprays are a temporary measure.
• Fruit splitting: Skin cracks open around the fruit. Caused by rapid water uptake after a dry period. Keep watering consistent, especially when fruits are swelling.
• Yellowing lower leaves: Normal as the season progresses – lower leaves age and die. Remove them to improve airflow. If upper leaves yellow, suspect magnesium deficiency (treat with Epsom salt solution) or overwatering.

Harvesting and storing tomatoes

Pick tomatoes when they are fully coloured and give slightly to gentle pressure. Don't wait for them to drop – that's past peak. In late season, green tomatoes can be harvested and ripened indoors on a windowsill or in a paper bag with a banana (ethylene from the banana speeds ripening).

Fresh tomatoes store best at room temperature, not in the fridge – cold temperatures destroy the flavour compounds that make home-grown tomatoes worth growing.