When to Plant Onion in Zone 10a

Allium cepa

Last updated: May 15, 2026 · Sources: USDA, NOAA, Cooperative Extension
Action Plan

Plant Onion in Zone 10a

  • Start indoors: Jan 13
  • Transplant: Feb 10 — after last frost (Feb 17)
  • First harvest: May 21 (90–120 days)
⚠️ Zone 10a last frost: Feb 17. Don't plant frost-sensitive crops before this date.
Last frost
Feb 17
First frost
Dec 3
Growing season
289 days
Zone 10a is the colder half of Zone 10

Zone 10a has a last frost around Feb 17 and first frost around Dec 3, giving you approximately 289 growing days. This is about 2 weeks shorter than Zone 10b. For more details see the Zone 10 complete guide.

Other Zones for Onion

Zone 3Zone 4Zone 5Zone 6Zone 7Zone 8Zone 9Zone 10Zone 11
📚 Data Sources
Frost dates: NOAA Climate Normals 1991–2020, National Centers for Environmental Information.
Hardiness zones: USDA Plant Hardiness Zone Map, Agricultural Research Service.
Growing requirements: Cooperative Extension Services — NC State, Penn State, University of Florida IFAS.
Companion planting: Cornell University Cooperative Extension.
Data compiled from public agricultural sources. Always verify with your local extension office for micro-climate adjustments.