How to grow onions

Onions start making bulbs when days reach a certain length, so the right type for your area matters more than almost anything else.

Reviewed October 2026

Plant outside

4–6 weeks before last spring frost (North)

Plant in fall

October in the South and Florida

Spacing

4–6 in

Days to harvest

100–130 for bulbs

Pick the right type for your area

Onions switch from growing leaves to forming bulbs when the days get long enough:

• Short-day onions start bulbing with about 10 to 12 hours of daylight. They're the type for the South and Florida, where they're planted in fall and harvested in spring.
• Long-day onions need 14 hours or more and are the type for northern gardens, planted in spring for a late-summer harvest.
• Intermediate (day-neutral) onions fall in between and suit the middle of the country.

Plant the wrong type and you'll get leaves but small bulbs, or bulbs that form too early.

When to plant

• In the North, plant sets or transplants in early spring, about 4 to 6 weeks before your last frost. Onions handle light frosts.
• In the South and Florida, plant short-day onions in fall, mostly in October, for bulbs in spring.

Look up your frost dates in the planting planner.

Planting and spacing

Sets (small dormant bulbs) and transplants are easier than seed. Plant them about 1 inch deep and 4 to 6 inches apart, in rows about 14 inches apart. For green onions, plant closer, about 2 inches apart, and pull them young.

Care

Onions have shallow roots, so keep them weeded and water regularly, especially while bulbs swell. Stop watering when the tops start to fall over.

Harvesting

Bulb onions take about 100 to 130 days. They're ready when most of the tops have flopped over and started to dry. Pull them, let them dry in a shady, airy spot for a couple of weeks, then trim the tops and store them somewhere cool and dry. Green onions are ready in about 50 to 75 days.

Planting dates in Florida