When to Plant Onion in Zone 9

Allium cepa

Last updated: Apr 29, 2026 · Sources: USDA, NOAA, Cooperative Extension
Action Plan

Plant Onion in Zone 9

  • Start indoors: Jan 31
  • Transplant: Feb 28 — after last frost (Feb 28)
  • First harvest: Jun 8 (90–120 days after planting)
⚠️ Don't plant before last frost (Feb 28) — cold snaps kill young transplants.
Last frost
Feb 28
First frost
Nov 25
Growing season
270 days
Quick Facts
Sunlight ☀️ Full Sun
Water Needs 💧💧 Moderate
Spacing 6 inches apart
Planting Depth 1.0 inch
Min Soil Temp 35°F
Germination 7–14 days
Days to Maturity 90–120 days
Frost Tolerance Heavy frost tolerance
Soil pH 6.0–7.0
Difficulty Moderate
What you'll need — Zone 9
🛒 Onion — Seeds & Supplies
  • 🌱 Onion Sets
  • 🌱 Long-Day Onion Seeds
  • 🌱 Onion Storage Mesh Bags

Search for these at your local garden center or nursery.

Growing Tips

  • Choose the right type for your latitude — long-day onions for north of 36°N, short-day for south.
  • Start from sets (small bulbs) for easiest growing.
  • Plant shallowly — just the tip below the soil surface.
  • Stop watering when tops start to fall over naturally — this signals bulb maturity.
  • Cure onions 2–4 weeks in a warm, dry, ventilated space before storing.

Common Mistakes

  • Choosing the wrong day-length type — long-day onions won't bulb in the south.
  • Planting too deep — onions need to sense day length through their tops.
  • Not curing properly — uncured onions rot quickly in storage.
  • Heavy nitrogen late in the season — encourages tops, not bulbs.

Companion Planting

Companion planting improves growth, deters pests, and makes better use of garden space.

✓ Good Companions

Carrot Beet Lettuce

✗ Avoid Nearby

Beans Peas

Onion Schedule — All Zones

ZoneStart IndoorsTransplant Direct SowHarvest StartHarvest End
Zone 3 Apr 17 May 15 May 15 Aug 23 Sep 12
Zone 4 Apr 12 May 10 May 10 Aug 18 Sep 22
Zone 5 Apr 2 Apr 30 Apr 30 Aug 8 Oct 2
Zone 6 Mar 18 Apr 15 Apr 15 Jul 24 Sep 22
Zone 7 Mar 8 Apr 5 Apr 5 Jul 14 Sep 12
Zone 8 Feb 20 Mar 20 Mar 20 Jun 28 Aug 27
Zone 9 Jan 31 Feb 28 Feb 28 Jun 8 Aug 7
Zone 10 Jan 13 Feb 10 Feb 10 May 21 Jul 20
Zone 11 Jan 1 Jan 15 Jan 15 Apr 25 Jun 24

Other Zones for Onion

Zone 3 · Zone 4 · Zone 5 · Zone 6 · Zone 7 · Zone 8 · Zone 10 · Zone 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.