When to Plant Onions
veg · hardy · ~100 days to harvest
Planting time for onions is set by your frost dates, not by the calendar month. Start seeds indoors about 10 weeks before your last spring frost, then transplant once the soil has warmed. From there it takes roughly 100 days to the first harvest. Onions is a hardy crop, and it keeps going about 21 days past a light frost, which is what makes a fall crop worth planting. Pick your zone below for exact dates, or find your zone by ZIP if you are not sure which one you are in.
When to plant onions by zone
| Zone | Last frost | Start indoors | In the ground | Spring harvest | Fall planting |
|---|---|---|---|---|---|
| Zone 3a | May 15 | Mar 6 | May 1 | Aug 9 | Aug 4 – Aug 25 |
| Zone 3b | May 13 | Mar 4 | Apr 29 | Aug 7 | Aug 7 – Aug 28 |
| Zone 4a | May 10 | Mar 1 | Apr 26 | Aug 4 | Aug 11 – Sep 1 |
| Zone 4b | May 5 | Feb 24 | Apr 21 | Jul 30 | Aug 17 – Sep 7 |
| Zone 5a | Apr 30 | Feb 19 | Apr 16 | Jul 25 | Aug 22 – Sep 12 |
| Zone 5b | Apr 25 | Feb 14 | Apr 11 | Jul 20 | Aug 27 – Sep 17 |
| Zone 6a | Apr 20 | Feb 9 | Apr 6 | Jul 15 | Sep 1 – Sep 22 |
| Zone 6b | Apr 15 | Feb 4 | Apr 1 | Jul 10 | Sep 6 – Sep 27 |
| Zone 7a | Apr 10 | Jan 30 | Mar 27 | Jul 5 | Sep 13 – Oct 4 |
| Zone 7b | Apr 3 | Jan 23 | Mar 20 | Jun 28 | Sep 20 – Oct 11 |
| Zone 8a | Mar 25 | Jan 14 | Mar 11 | Jun 19 | Sep 27 – Oct 18 |
| Zone 8b | Mar 15 | Jan 4 | Mar 1 | Jun 9 | Oct 4 – Oct 25 |
| Zone 9a | Mar 1 | Dec 21 | Feb 15 | May 26 | Oct 19 – Nov 9 |
| Zone 9b | Feb 15 | Dec 7 | Feb 1 | May 12 | Oct 29 – Nov 19 |
| Zone 10a | Jan 31 | Nov 22 | Jan 17 | Apr 27 | Nov 8 – Nov 29 |
| Zone 10b | Jan 15 | Nov 6 | Jan 1 | Apr 11 | Nov 19 – Dec 10 |
| Zone 11a | none | Feb 1 | Feb 1 | May 12 | Oct onward |
| Zone 11b | none | Feb 1 | Feb 1 | May 12 | Oct onward |
| Zone 12a | none | Feb 1 | Feb 1 | May 12 | Oct onward |
| Zone 12b | none | Feb 1 | Feb 1 | May 12 | Oct onward |
| Zone 13a | none | Feb 1 | Feb 1 | May 12 | Oct onward |
| Zone 13b | none | Feb 1 | Feb 1 | May 12 | Oct onward |
Dates use the representative frost window for each zone. Your own ZIP will differ by a week or two: look it up here.
Planting onions in fall
Short-day onion sets planted in fall overwinter in zone 7 and warmer and bulb up months ahead of a spring planting.
The timing rule is roughly 6 to 3 weeks before the average first frost. Planting earlier pushes soft growth that winter kills; planting later leaves the roots too shallow to hold through a freeze. The coldest zone where this still works on the averages is Zone 3a.
For the whole-garden version of this arithmetic, see the fall planting calendar by zone, and how to read and stretch your first frost date.
When to plant onions in 12 US cities
These use each city's own NOAA frost dates rather than its zone average, which is why two cities in the same zone can differ by a week or more. Texas alone spans a wide range: in Houston (Zone 9a) onions go in around Jan 30 in spring and Oct 28 to Nov 18 to overwinter; in Dallas (Zone 8a) onions go in around Feb 22 in spring and Oct 13 to Nov 3 to overwinter.
| City | Zone | Last frost | In the ground (spring) | Fall planting |
|---|---|---|---|---|
| New York, NY | 7b | Mar 30 | Mar 16 | Oct 9 – Oct 30 |
| Los Angeles, CA | 10b | none | Oct to Feb (cool season) | Oct onward |
| Chicago, IL | 6a | Apr 16 | Apr 2 | Sep 16 – Oct 7 |
| Houston, TX | 9a | Feb 13 | Jan 30 | Oct 28 – Nov 18 |
| Phoenix, AZ | 9b | none | Oct to Feb (cool season) | Oct onward |
| Philadelphia, PA | 7b | Apr 2 | Mar 19 | Sep 29 – Oct 20 |
| Atlanta, GA | 8a | Mar 15 | Mar 1 | Oct 9 – Oct 30 |
| Dallas, TX | 8a | Mar 8 | Feb 22 | Oct 13 – Nov 3 |
| Denver, CO | 6a | May 5 | Apr 21 | Aug 28 – Sep 18 |
| Seattle, WA | 8b | Mar 2 | Feb 16 | Oct 12 – Nov 2 |
| Minneapolis, MN | 4b | Apr 23 | Apr 9 | Sep 6 – Sep 27 |
| Miami, FL | 11a | none | Oct to Feb (cool season) | Oct onward |
What to plant with onions
Onions grow well next to carrots, beets, tomatoes and kale. Keep them away from beans (bush) and peas. The sulfur compounds that repel many pests also suppress the rhizobia legumes need to fix nitrogen. The full grid for all 24 crops is in the companion planting chart.
Onions zone pages
More on growing onions
- When to plant garlic by zone
The fall planting window for garlic and other alliums in every zone.
- When to start seeds indoors by zone
Indoor start dates for onions, counted back from your last frost.
- Hardening off seedlings: a schedule
A day by day plan for moving onions seedlings outdoors.
- Best grow lights for seed starting
What light seedlings actually need, and which fixtures deliver it.
- Seed-starting setup: what you actually need
Trays, mix, heat and light for starting onions indoors.
- Last frost date and what to plant before it
Why onions can go out before your last frost, and how far before.
Frequently asked questions
When can I plant onions?
In fall, around your first frost. Short-day onion sets planted in fall overwinter in zone 7 and warmer and bulb up months ahead of a spring planting.
How long does onions take to grow?
About 100 days from transplant or sowing to harvest.
Is onions frost-hardy?
Onions is a hardy crop. It tolerates light frost and can go out early. In fall it keeps going about 21 days past the first light frost.
Can you plant onions in the fall?
Yes, and fall is the main planting season for it. Plant roughly 6 to 3 weeks before the average first frost for your zone. Short-day onion sets planted in fall overwinter in zone 7 and warmer and bulb up months ahead of a spring planting.
What is the latest I can plant onions?
It depends on your first frost date. In Zone 6a, sow by Sep 22; In Zone 7a, sow by Oct 4; In Zone 8a, sow by Oct 18. Colder zones are earlier, warmer zones later.