When to plant onions
Short answer
Plant onions about 4 weeks before your last spring frost. In a mid climate (zone 5) that's around Mar 18, starting seeds indoors about Feb 4. Enter your ZIP for your exact dates.
| Climate zone | Start indoors | Plant outside | Harvest |
|---|---|---|---|
| Zone 1 | Nov 6 | Dec 18 | Mar 28 |
| Zone 2 | Dec 7 | Jan 18 | Apr 28 |
| Zone 3 | Dec 30 | Feb 10 | May 21 |
| Zone 4 | Jan 19 | Mar 2 | Jun 10 |
| Zone 5 | Feb 4 | Mar 18 | Jun 26 |
| Zone 6 | Feb 19 | Apr 2 | Jul 11 |
| Zone 7 | Mar 6 | Apr 17 | Jul 26 |
| Zone 8 | Mar 23 | May 4 | Aug 12 |
Higher climate-zone numbers are colder, so planting shifts later. Onions is a hardy crop. Enter your ZIP in the calculator for your exact zone and dates.
What sets the timing for onions
When to plant onions comes down to one date: your last spring frost. Onions is a hardy crop, so it goes in about 4 weeks before your last spring frost. In a mid climate (zone 5) that's around Mar 18.
Give it a head start: sow seeds indoors about 10 weeks before your last spring frost (around Feb 4 in zone 5), then move seedlings out once conditions are right. From there it's roughly 100 days to harvest.
Because that anchor date moves with climate, plant-out for onions ranges from about Feb 10 in warm zone 3 to Apr 17 in cold zone 7. Enter your ZIP in the calculator for the exact dates in your zone.
What sets the timing
| Factor | Effect on timing |
|---|---|
| Frost anchor | Timing counts from your last spring frost |
| Hardiness | Onions is hardy — it goes in before the last frost |
| Indoor start | Start seeds 10 weeks before your last spring frost |
| Days to harvest | About 100 days from planting to harvest |
| Climate zone | Higher (colder) zones push plant-out later; warmer zones let you start sooner |
| Soil & weather | Tolerates cool soil and light frost |
How onions compares
Plant-out date in a mid climate (zone 5), against an early hardy crop and a late tender one.
| Crop | Plant outside (zone 5) |
|---|---|
| Peas (hardy · plants early) | Mar 11 |
| Onions | Mar 18 |
| Tomatoes (tender · plants late) | Apr 29 |
Tips for growing onions
- Start onions early — it tolerates cool soil and a light frost, so you can plant before your last spring frost.
- Give onions a 10 weeks indoor head start under a bright light before transplanting.
- Count roughly 100 days from planting to harvest, and stagger sowings a few weeks apart for a longer picking window.
- Enter your ZIP in the calculator for onions dates tuned to your exact climate zone.
Your exact dates
Open the planting calendarOther crops
Frequently asked questions
When should I plant onions?
Plant onions about 4 weeks before your last spring frost. In a warmer zone 4 that's around Mar 2; in a colder zone 6, Apr 2.
When do I start onions seeds indoors?
Start onions seeds indoors about 10 weeks before your last frost, then transplant after the frost passes. That's roughly Feb 19 in zone 6.
How long until onions is ready to harvest?
About 100 days from planting until first harvest. In zone 6, onions planted around Apr 2 is typically ready near Jul 11.