How to Start Broccoli From Seed
Broccoli is commonly started indoors for a sturdy transplant and an earlier harvest. It grows best in cool weather, so timing is more important than rushing it into summer heat.
Start indoors or direct sow?
Start broccoli indoors and transplant it outdoors, especially for spring crops. Direct sowing is possible in mild climates, but indoor starts offer better spacing and a more dependable spring schedule.
When to start Broccoli seeds
For a spring crop, start seeds indoors 4 to 6 weeks before the average last spring frost and transplant about 2 to 3 weeks before that frost date if plants are hardened off. For fall harvest, start seeds indoors 5 to 7 weeks before setting plants out, usually in mid to late summer for your area.
How to sow the seeds
Sow seeds 1/4 inch deep in sterile seed-starting mix, using cell trays or small pots with drainage. Start one or two seeds per cell, then keep the mix moist and provide bright light as soon as seedlings emerge.
Germination
Broccoli generally germinates in 4 to 10 days. Maintain evenly moist, not soggy, mix and soil temperatures around 65 to 75°F for reliable sprouting.
Seedling care
After emergence, provide strong light for 14 to 16 hours daily indoors and keep seedlings cool enough to prevent stretching. Water from below or at the soil line, provide airflow, and thin to one strong seedling per cell to reduce damping off.
Transplanting & hardening off
Harden seedlings off over 7 to 10 days, then transplant when they have several true leaves and daytime conditions are cool. Set plants at the same depth they grew in their cells, water them in well, and protect against a hard freeze with row cover if necessary.
Tips
Avoid letting transplants become rootbound, since crowded plants may form smaller heads. Choose a variety suited to either spring or fall production in your region.
General seed-starting guidance for US home gardens; timing depends on your local frost dates and variety. Page updated Aug 4, 2026.