When to Plant Onions in Illinois
In Illinois, the time to plant onions outside runs from Mar 13 – Mar 27 in Chicago to Apr 2 – Apr 16 in Waukegan. In Chicago, it's Mar 13 – Mar 27. The average last spring frost differs by about 3 weeks across the state (Apr 10 in Chicago, Apr 30 in Waukegan), 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 Illinois by city
| City | Zone | Start indoors | Plant outside |
|---|---|---|---|
| Arlington Heights | 6a | Jan 25 – Feb 8 | Mar 22 – Apr 5 |
| Aurora | 5b | Jan 25 – Feb 8 | Mar 22 – Apr 5 |
| Bartlett | 5b | Feb 5 – Feb 19 | Apr 2 – Apr 16 |
| Belleville | 7a | Jan 18 – Feb 1 | Mar 15 – Mar 29 |
| Berwyn | 6a | Jan 17 – Jan 31 | Mar 14 – Mar 28 |
| Bloomington | 6a | Jan 31 – Feb 14 | Mar 28 – Apr 11 |
| Bolingbrook | 6a | Jan 26 – Feb 9 | Mar 23 – Apr 6 |
| Buffalo Grove | 6a | Jan 25 – Feb 8 | Mar 22 – Apr 5 |
| Champaign | 6a | Jan 21 – Feb 4 | Mar 18 – Apr 1 |
| Chicago | 6a | Jan 16 – Jan 30 | Mar 13 – Mar 27 |
| Cicero | 6a | Jan 17 – Jan 31 | Mar 14 – Mar 28 |
| Crystal Lake | 5b | Jan 31 – Feb 14 | Mar 28 – Apr 11 |
| Decatur | 6a | Jan 20 – Feb 3 | Mar 17 – Mar 31 |
| Des Plaines | 6a | Jan 22 – Feb 5 | Mar 19 – Apr 2 |
| Downers Grove | 6a | Feb 3 – Feb 17 | Mar 31 – Apr 14 |
| Elgin | 5b | Feb 1 – Feb 15 | Mar 29 – Apr 12 |
| Elmhurst | 6a | Jan 22 – Feb 5 | Mar 19 – Apr 2 |
| Evanston | 6a | Feb 1 – Feb 15 | Mar 29 – Apr 12 |
| Glenview | 6a | Feb 1 – Feb 15 | Mar 29 – Apr 12 |
| Hoffman Estates | 5b | Feb 5 – Feb 19 | Apr 2 – Apr 16 |
| Joliet | 5b | Jan 25 – Feb 8 | Mar 22 – Apr 5 |
| Lombard | 6a | Feb 3 – Feb 17 | Mar 31 – Apr 14 |
| Moline | 5b | Jan 30 – Feb 13 | Mar 27 – Apr 10 |
| Mount Prospect | 6a | Jan 25 – Feb 8 | Mar 22 – Apr 5 |
| Naperville | 5b | Feb 3 – Feb 17 | Mar 31 – Apr 14 |
| Normal | 6a | Jan 31 – Feb 14 | Mar 28 – Apr 11 |
| Oak Lawn | 6a | Jan 16 – Jan 30 | Mar 13 – Mar 27 |
| Oak Park | 6a | Jan 17 – Jan 31 | Mar 14 – Mar 28 |
| Orland Park | 6a | Jan 25 – Feb 8 | Mar 22 – Apr 5 |
| Palatine | 5b | Jan 31 – Feb 14 | Mar 28 – Apr 11 |
| Peoria | 6a | Jan 22 – Feb 5 | Mar 19 – Apr 2 |
| Plainfield | 5b | Jan 26 – Feb 9 | Mar 23 – Apr 6 |
| Rockford | 5b | Jan 30 – Feb 13 | Mar 27 – Apr 10 |
| Romeoville | 6a | Jan 26 – Feb 9 | Mar 23 – Apr 6 |
| Schaumburg | 5b | Feb 5 – Feb 19 | Apr 2 – Apr 16 |
| Skokie | 6a | Feb 1 – Feb 15 | Mar 29 – Apr 12 |
| Springfield | 6a | Jan 21 – Feb 4 | Mar 18 – Apr 1 |
| Tinley Park | 6a | Jan 29 – Feb 12 | Mar 26 – Apr 9 |
| Waukegan | 6a | Feb 5 – Feb 19 | Apr 2 – Apr 16 |
| Wheaton | 5b | Feb 3 – Feb 17 | Mar 31 – Apr 14 |
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 Illinois, or the general guide to when to plant onions.
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