Starting Tomatoes Indoors: Light, Timing and Pricking Out

The right timing

Tomatoes are usually started indoors from mid-March to early April. If you have a very bright growing space or grow lights, you can start a little earlier. Without extra light, sowing too early often leads to tall, weak seedlings.

• February: only useful with a very bright spot or grow lights
• March: the main and most reliable sowing month
• April: still possible, especially for fast-growing varieties

Temperature for germination and growth

Tomato seeds germinate best with steady warmth. During germination, about 20 to 24 °C is suitable. Once seedlings appear, they should be moved to a very bright and slightly cooler place to keep growth compact.

• Germination stage: keep warm and evenly moist
• After sprouting: move into strong light
• Avoid places that are both warm and dim

Light: the most important factor

After germination, tomatoes need as much light as possible. A south-facing window, bright conservatory, or suitable grow light helps produce short, sturdy young plants.

• Move seedlings into bright light as soon as they emerge
• Turn pots regularly so plants grow straight
• Long, pale green stems usually mean the spot is too dark

How to sow tomatoes step by step

1. 1

   Prepare the container

   Fill seed trays or small pots with loose, low-nutrient seed-starting mix.

2. 2

   Sow the seeds

   Place the seeds with some spacing and cover them lightly with soil.

3. 3

   Moisten gently

   Water carefully so the seeds are not washed away.

4. 4

   Keep warm

   Place the tray in a warm spot and keep the soil evenly moist but not wet.

5. 5

   Move to light after germination

   Once seedlings appear, give them plenty of light and slightly cooler conditions.

Pricking out: when and how

Prick out tomato seedlings when the first true leaves appear after the seed leaves. At this stage, each plant needs its own pot and more room for roots and leaves.

1. 1

   Lift the seedlings

   Carefully lift seedlings from the soil with a dibber, spoon, or similar tool.

2. 2

   Pot individually

   Move each plant into its own pot filled with loose growing medium.

3. 3

   Plant deeper

   Set tomatoes a little deeper so they can form extra roots along the stem.

4. 4

   Water in

   Water gently and place the plants in bright light, but not immediately in harsh midday sun.

Care until planting out

Until planting out, young tomatoes need strong light, moderate moisture, and enough space. The soil should not dry out completely, but constantly wet pots weaken the roots.

• Water evenly but sparingly
• Move plants into larger pots when needed
• Start hardening off on mild days from April
• Plant outdoors permanently only after the last frosts

Common mistakes to avoid

• Sowing too early without extra light
• Keeping seedlings too warm after germination
• Waterlogging in seed trays
• Pricking out too late when seedlings are crowded
• Moving plants outdoors without hardening them off

Frequently asked questions