When to Plant Onions in Iowa
In Iowa, the time to plant onions outside runs from Mar 18 – Apr 1 in Burlington to Apr 3 – Apr 17 in Spencer. In Des Moines, it's Mar 21 – Apr 4. The average last spring frost differs by about 2 weeks across the state (Apr 15 in Burlington, May 1 in Spencer), so use the dates for the town nearest you.
Onions are cold-hardy. Plant sets or transplants early so they grow leaves before long summer days trigger bulbing.
- Start indoors: 10–12 weeks before the last frost.
- Plant outside: 2–4 weeks before the last frost.
Onions planting dates in Iowa by city
| City | Zone | Start indoors | Plant outside |
|---|---|---|---|
| Altoona | 5b | Jan 29 – Feb 12 | Mar 26 – Apr 9 |
| Ames | 5b | Feb 1 – Feb 15 | Mar 29 – Apr 12 |
| Ankeny | 5b | Jan 29 – Feb 12 | Mar 26 – Apr 9 |
| Bettendorf | 5b | Jan 22 – Feb 5 | Mar 19 – Apr 2 |
| Boone | 5a | Feb 3 – Feb 17 | Mar 31 – Apr 14 |
| Burlington | 6a | Jan 21 – Feb 4 | Mar 18 – Apr 1 |
| Cedar Falls | 5a | Feb 2 – Feb 16 | Mar 30 – Apr 13 |
| Cedar Rapids | 5b | Feb 2 – Feb 16 | Mar 30 – Apr 13 |
| Clinton | 5b | Jan 28 – Feb 11 | Mar 25 – Apr 8 |
| Clive | 5b | Jan 24 – Feb 7 | Mar 21 – Apr 4 |
| Coralville | 5b | Jan 27 – Feb 10 | Mar 24 – Apr 7 |
| Council Bluffs | 5b | Jan 24 – Feb 7 | Mar 21 – Apr 4 |
| Davenport | 5b | Jan 25 – Feb 8 | Mar 22 – Apr 5 |
| Des Moines | 5b | Jan 24 – Feb 7 | Mar 21 – Apr 4 |
| Dubuque | 5a | Jan 25 – Feb 8 | Mar 22 – Apr 5 |
| Fort Dodge | 5a | Feb 3 – Feb 17 | Mar 31 – Apr 14 |
| Grimes | 5b | Jan 25 – Feb 8 | Mar 22 – Apr 5 |
| Indianola | 5b | Jan 30 – Feb 13 | Mar 27 – Apr 10 |
| Iowa City | 5b | Jan 27 – Feb 10 | Mar 24 – Apr 7 |
| Johnston | 5b | Jan 25 – Feb 8 | Mar 22 – Apr 5 |
| Le Mars | 5a | Feb 5 – Feb 19 | Apr 2 – Apr 16 |
| Marion | 5a | Feb 3 – Feb 17 | Mar 31 – Apr 14 |
| Marshalltown | 5a | Feb 3 – Feb 17 | Mar 31 – Apr 14 |
| Mason City | 5a | Feb 4 – Feb 18 | Apr 1 – Apr 15 |
| Muscatine | 5b | Jan 30 – Feb 13 | Mar 27 – Apr 10 |
| Newton | 5b | Jan 28 – Feb 11 | Mar 25 – Apr 8 |
| North Liberty | 5b | Jan 27 – Feb 10 | Mar 24 – Apr 7 |
| Norwalk | 5b | Jan 24 – Feb 7 | Mar 21 – Apr 4 |
| Oskaloosa | 5b | Jan 27 – Feb 10 | Mar 24 – Apr 7 |
| Ottumwa | 5b | Jan 29 – Feb 12 | Mar 26 – Apr 9 |
| Pella | 5b | Jan 26 – Feb 9 | Mar 23 – Apr 6 |
| Pleasant Hill | 5b | Jan 24 – Feb 7 | Mar 21 – Apr 4 |
| Sioux City | 5a | Feb 4 – Feb 18 | Apr 1 – Apr 15 |
| Spencer | 5a | Feb 6 – Feb 20 | Apr 3 – Apr 17 |
| Storm Lake | 5a | Jan 31 – Feb 14 | Mar 28 – Apr 11 |
| Urbandale | 5b | Jan 25 – Feb 8 | Mar 22 – Apr 5 |
| Waterloo | 5a | Feb 2 – Feb 16 | Mar 30 – Apr 13 |
| Waukee | 5b | Jan 24 – Feb 7 | Mar 21 – Apr 4 |
| Waverly | 5a | Feb 2 – Feb 16 | Mar 30 – Apr 13 |
| West Des Moines | 5b | Jan 24 – Feb 7 | Mar 21 – Apr 4 |
Calculated from each town's average (50%) frost dates, from the nearest NOAA station (1991–2020). Typical dates for the 2027 planting season, based on NOAA's 1991–2020 averages. They are long-term odds, not a forecast: always check your local forecast before planting. Zones: 2023 USDA Plant Hardiness Zone Map (USDA-ARS and Oregon State University). Not the official map; see planthardiness.ars.usda.gov.
See all frost dates in Iowa, or the general guide to when to plant onions.
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