How to Start Tomatoes From Seed
Tomatoes are easy to start indoors and benefit from a long head start before warm outdoor weather arrives. Growing your own seedlings also gives you access to many varieties not commonly sold as transplants.
Start indoors or direct sow?
Start tomatoes indoors, then transplant them outdoors. They need a long growing season and tolerate transplanting well, especially when planted deeply.
When to start Tomatoes seeds
Sow indoors about 6 to 8 weeks before your average last spring frost. Transplant after frost danger has passed and nighttime temperatures are reliably above about 50°F.
How to sow the seeds
Sow seeds 1/4 inch deep in sterile seed-starting mix in cells or small pots with drainage. Use a humidity dome until emergence, then remove it and grow seedlings in 2 to 4 inch containers if they outgrow their cells.
Germination
Tomato seeds usually germinate in 5 to 10 days. Keep the mix evenly moist, not soggy, at about 65 to 85°F, with faster germination near the warmer end of that range.
Seedling care
Provide strong light for 14 to 16 hours daily, ideally from a grow light placed close above the leaves. Water from below or at soil level, use airflow, and let the surface dry slightly between waterings to reduce damping off.
Transplanting & hardening off
Harden seedlings off over 7 to 10 days before planting them outside. Set them in full sun after frost, burying part of the stem so only the upper leaves remain above soil.
Tips
Use a small fan for gentle airflow to encourage sturdy stems. Pot seedlings up before they become root-bound, especially if outdoor planting is delayed.
General seed-starting guidance for US home gardens; timing depends on your local frost dates and variety. Page updated Aug 4, 2026.