The Beginner’s Guide to Growing Tomatoes (Step-by-Step)
Updated: Sep 30
To grow tomatoes (Solanum lycopersicum) from seed, sow them indoors 6 to 8 weeks before your last frost, keep them at 18 to 22°C in bright light, then plant them out deeply once nights stay above 10°C. In Ireland and the UK that means sowing in March and planting out in late May or June, ideally in a greenhouse or polytunnel. Expect your first ripe fruit 60 to 85 days after planting out.
Homegrown tomatoes taste far better than supermarket ones, which are bred for shelf life rather than flavour. This guide covers every step, from choosing varieties that suit a cool climate to harvesting, using regenerative, chemical-free methods.
Tomato Quick Facts
Latin name: Solanum lycopersicum
Sow indoors: March (6 to 8 weeks before last frost)
Germination temperature: 18 to 24°C
Germination time: 5 to 10 days
Plant out: Late May to June, when nights stay above 10°C
Position: Full sun (6 to 8 hours); greenhouse or polytunnel best in Ireland
Soil: Rich, moist, well-drained, full of compost
Spacing: 45 to 60 cm
Days to harvest: 60 to 85 after planting out
Hardiness: Frost tender
Step 1: Choose Tomatoes That Suit Your Climate
In a cool, short summer like Ireland’s, variety choice matters more than anything else.
Outdoors in Ireland and the UK: choose early, cold-tolerant varieties such as ‘Stupice’, ‘Glacier’ or ‘Sub Arctic Plenty’, and cherry types, which ripen fastest.
Greenhouse or polytunnel: almost anything works, including beefsteak, plum and heritage varieties.
Containers and balconies: compact bush (determinate) types are easiest.
Our own seed range includes Atomic Grape and Dark Galaxy (striking cherry and small-fruited types), plus classic plum and beef tomatoes for the greenhouse.
Step 2: Sow the Seeds Indoors
Sow in March in small pots or modules of fine seed compost, 0.5 cm deep.
Keep at 18 to 24°C, on a warm windowsill or heated propagator.
Once seedlings appear (5 to 10 days), move them to the brightest spot you have, or under a grow light, to stop them getting leggy.
When they have their first true leaves, pot them on individually into 9 cm pots, burying the stem up to the leaves.
Step 3: Harden Off and Plant Out
Harden plants off over 7 to 10 days before planting outside. In Ireland, plant into a greenhouse or polytunnel from mid-May, or outdoors against a sunny, sheltered wall from early June.
Plant deep: bury the stem up to the lowest leaves. Tomatoes root along buried stems, giving a stronger plant.
Space well: 45 to 60 cm apart, for airflow that helps prevent blight.
Containers: use pots at least 30 cm deep and wide, filled with rich, compost-based mix.
Step 4: Support and Prune
Cordon (indeterminate) types: grow up a stake or string. Pinch out side shoots in the leaf joints every week so the plant puts its energy into fruit.
Bush (determinate) types: need a short cage or stake but no side-shooting.
Stopping: in Ireland, pinch out the growing tip of cordons in August, after 4 to 6 trusses have set, so the existing fruit has time to ripen.
Step 5: Water and Feed
Water deeply and regularly at the base. Irregular watering causes blossom end rot and split fruit.
Mulch with compost, straw or grass clippings to hold moisture.
Tomatoes are hungry. Start with plenty of compost, then feed every 1 to 2 weeks once the first fruits set. Comfrey tea, made by soaking leaves of
in water for a few weeks, is a free, high-potassium tomato feed.
Step 6: Harvest
Pick tomatoes when they are fully coloured but still firm. At the end of the season, before the first frost, pick any green fruit and ripen it indoors next to a banana, or turn it into green tomato chutney.
Common Tomato Problems and How to Fix Them
Blight: the biggest threat in wet Irish summers. Brown patches spread fast on leaves and fruit. Grow under cover if you can, water at the base, remove affected leaves immediately, and consider blight-resistant varieties.
Blossom end rot: a black patch on the base of the fruit, caused by irregular watering. Keep watering consistent.
Split fruit: caused by heavy watering or rain after a dry spell.
Leggy seedlings: not enough light. Move them to a brighter spot and keep them cooler at night.
Aphids and whitefly: plant basil, marigolds and nasturtiums nearby, and encourage ladybirds and hoverflies.
Companion Plants for Tomatoes
Can Tomatoes Grow in a Food Forest?
Tomatoes are annuals that need full sun, so they suit the early years of a food forest, before trees and shrubs create shade. Plant them in sunny gaps between young fruit trees to get a harvest while the perennial layers establish. For a similar fruit that tolerates a little more shade, try physalis (Cape gooseberry), which can be grown from our physalis seeds.
FAQ: Growing Tomatoes
When should I sow tomato seeds in Ireland?
Sow tomato seeds indoors in March, about 6 to 8 weeks before the last frost. Plant them into a greenhouse or polytunnel from mid-May, or outdoors in a sheltered, sunny spot from early June.
Can you grow tomatoes outside in Ireland?
Yes, but choose early, cold-tolerant or cherry varieties and plant them against a sunny, sheltered wall. Outdoor tomatoes in Ireland are more prone to blight, so a greenhouse or polytunnel gives far more reliable crops.
How long do tomatoes take to grow from seed?
Tomato seeds germinate in 5 to 10 days. Most varieties produce ripe fruit 60 to 85 days after planting out, which means around 4 to 5 months from sowing to first harvest.
Should I remove tomato side shoots?
Yes, on cordon (indeterminate) varieties. Pinch out side shoots weekly so the plant focuses on fruit. Bush (determinate) varieties don’t need side-shooting.
How do I stop tomato blight?
Grow under cover if possible, space plants well, water at the base rather than over the leaves, and remove affected leaves at the first sign of brown patches. Blight-resistant varieties help in wet summers.
Get Started This Spring
Tomatoes are one of the most rewarding crops you can grow, and seed is by far the cheapest way to start. Our tomato seed range, including Atomic Grape, Dark Galaxy, plum and beef varieties, is ready for March sowing.
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