How to Grow Onion (2026)
Day-length specific; sets or transplants.
Quick answer: Onion is a cool-season crop for zones 3–11 in full sun. Plant 2–4 weeks before the last frost or in fall, space 4″ apart, and expect harvest in about 100 days.
Build your Onion planting card
Pick your state for indoor-start, sow/transplant, and harvest dates you can print.
In Alabama (zone 7–9, last frost ≈ Mar 15, first frost ≈ Nov 15, 245-day season), your Onion plan:
Day-length specific; sets or transplants. Suits USDA zones 3–11. Dates are typical; confirm with your county extension and the 10-day forecast.
Growing tips
- Spacing: 4 inches between plants keeps air flowing and limits disease.
- Depth: sow seeds about 0.5″ deep (or set transplants at the same soil line).
- Sun: Full sun (6+ hours).
- Season: Tolerates light frost; best in cool weather, sow in spring and again in fall.
More cool-season crops
Spacing, depth, and days-to-harvest are typical values from university extension guides. Planting dates are computed from typical USDA/extension freeze dates (USDA Plant Hardiness Zone Map (2023) + state cooperative extension typical freeze dates); confirm locally before acting.