How to Grow Onion

Start Onion seeds indoors 8 weeks before your last frost date, then transplant outdoors 2 weeks after the last frost. Use the search on this page to find exact dates for your ZIP code or city.

Onion typically matures in about 100 days from planting. Exact timing varies by variety, soil conditions, and local climate.

Onion should be started indoors 8 weeks before the last frost date. This gives seedlings time to establish before being transplanted outside after frost danger has passed.

Onion requires full sun (6+ hours) to thrive.

Space Onion plants 4 inches apart to allow adequate airflow and root development.

Onion has moderate water needs. Consistent moisture is important especially during germination and early growth.

Yes — seed saving difficulty for Onion is rated moderate. Allow seed heads to form in year 2 (onions are biennial). Harvest when most seeds are black and visible. Cut seed heads into bags, dry 1 week, shake to release seeds.

Properly dried and stored Onion seeds remain viable for up to 1 year. Store in a cool, dark, dry location in an airtight container with a silica gel packet for best results.

Yes — Onion is open-pollinated, meaning seeds saved from your harvest will grow plants true to the parent variety. This makes it an excellent candidate for building a self-sustaining garden.