Starting Seeds Indoors

Sowing

Starting seeds indoors gives tender vegetables, flowers and herbs a useful head start before outdoor conditions are reliable. It is especially worthwhile for tomatoes, chillies, aubergines and bedding plants. Use clean containers, fresh compost and enough light, then raise plants steadily rather than forcing rapid, soft growth.

How to do it

Fill module trays, seed trays or small pots with moist peat-free seed compost, firming it lightly. Sow at the depth stated on the packet, usually no deeper than twice the seed's width, and label each sowing with variety and date. Cover fine seed only where the packet advises. Water gently, preferably from below, and place containers in a warm propagator, greenhouse or bright windowsill. Remove any cover as soon as seedlings emerge, then give bright light and moderate watering. Turn trays regularly on a windowsill so growth stays even. Prick out crowded seedlings once they have their first true leaves, and pot on rooted plants before their containers become full of roots.

When to do it

For most tender crops, sow from February to April, following the packet guidance and your available warmth and light. Earlier sowings need reliable heat and supplementary light can be helpful. In colder parts of the UK, or where planting space is exposed, delay tender plants slightly so they are not ready before frost risk has passed.

Tips

Do not sow too early simply because the greenhouse or windowsill is available. Leggy seedlings are usually short of light or too warm. Keep compost just moist, not saturated, and avoid standing pots in water for long periods. Label immediately, as many young plants look remarkably alike at first.

Starting Seeds Indoors: frequently asked questions

How does starting seeds indoors work?

Fill module trays, seed trays or small pots with moist peat-free seed compost, firming it lightly.

When should I do starting seeds indoors?

For most tender crops, sow from February to April, following the packet guidance and your available warmth and light.

What are some tips for starting seeds indoors?

Do not sow too early simply because the greenhouse or windowsill is available.

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General guidance for UK gardens. Page updated 19 Sep 2026.