1. Considering climatic conditions

Sowing times depend primarily on when you plan to transplant the seedlings into open ground or a greenhouse:

In central Ukraine and Russia, tomato seedlings are typically sown in late February or early March, with transplanting them into a greenhouse by mid- to late May.
For open ground, seedlings are sown 6-8 weeks before the expected planting date, given that tomatoes are sensitive to frost.
2. Sowing times by variety
Early varieties are sown for seedlings approximately 50-60 days before transplanting into the ground. Mid-season varieties germinate in 60–70 days.
Late varieties germinate in 70–80 days to give them more time to develop.
3. Temperature and Light
Seeds germinate best at a temperature of 22–25°C.
After germination, seedlings should be kept at 18–20°C during the day and 15–16°C at night to prevent stretching.
Adequate lighting is the key to strong seedlings. If natural light is insufficient, use phytolamps.
4. Seed and Soil Preparation
Before sowing, seeds are soaked for 8–12 hours in warm water or a weak solution of potassium permanganate to disinfect.
The soil should be light, nutritious, and moisture-retentive, preferably with the addition of humus and compost.
5. Additional Tips
After the first two true leaves appear, the seedlings are pricked out to give the roots more space. Before planting outdoors, seedlings are gradually hardened off by placing them outside for several hours a day.

Choosing the right sowing time and caring for your seedlings will ensure strong plants and a bountiful harvest of delicious tomatoes in the summer.