Growing onions (bulbing): timing, spacing and costs by zone

When to plant

Onions (bulbing): cool-season, hardy to frost. Plant when soil reaches 50–75°F. Dates below are averages worked out from each zone's frost dates — check your own field.

• Zone 6b (Boone NC): set out March 6 – March 27. First picking around June 21 – July 19.
• Zone 7b (Raleigh): set out February 18 – March 11. First picking around June 5 – July 3.
• Zone 8b (Charleston SC): set out January 25 – February 15. First picking around May 12 – June 9.
• Zone 9a (Gainesville FL): set out January 7 – January 28. First picking around April 24 – May 22.

Setting it up

Grow as transplants, started about 10 weeks before last frost. Space plants 4 inches apart in rows 12 inches apart, about 0.25 inch deep. Expect roughly 100 days to first harvest.

Field notes

Southeast growers must plant short-day varieties. Long-day types will make tops but never bulb below 36° latitude.

How it fits each zone

• Zone 6b: challenging — Short-day onion varieties bulb best in Zones 7 and warmer; northern growers should choose intermediate-day types instead.
• Zone 7b: excellent — Onions (bulbing) is well suited to Zone 7b. Standard planting dates work with minor adjustments for microclimates.
• Zone 8b: excellent — Onions (bulbing) is well suited to Zone 8b. Standard planting dates work with minor adjustments for microclimates.
• Zone 9a: good — Cool-season crops bolt fast under Zone 9a heat. Prioritize the fall planting window and use shade cloth for any spring succession.

What it costs per acre

• 2024 Western Colorado Onions (Furrow Irrigated) — Estimated Production Costs & Returns (Colorado State University Extension — Agriculture & Business Management, 2024): about $8,791 per acre in transcribed costs.

These are published budgets, not your costs. Plug your own numbers into the breakeven calculator before you commit ground.

Before you plant

Line up who will buy it and at what price before seed goes in the ground. See the planting calendar for your exact zone.