Oswego, IL frost dates
Last spring frostApr 19median date
First fall frostOct 23median date
Growing season187 daysfrost-free
Hardiness zone5bZone 5b
How Oswego compares
- In 8 years out of 10, the last spring frost in Oswego falls between April 5 and May 4, a 29-day window. The first fall frost falls between October 9 and November 3.
- The median last frost is 2 days later than the Illinois median of Apr 17.
- Its 187-day growing season is longer than 48% of the 1,287 Illinois places with a regular frost season (state median 187 days).
- The last frost is 12 days earlier than the zone 5b median of May 1. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 5b chart.
- The weather station records an average of 134 nights a year at or below 32°F.
- Oswego shares its weather station with Aurora, IL, 12 km away, so the two have the same frost dates.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 5 |
| 50% (median) | April 19 |
| 10% (safe for tender plants) | May 4 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | October 9 |
| 50% (median) | October 23 |
| 90% (late) | November 3 |
Frost here means 32°F (0°C). A median date means half of years have their last frost earlier and half later.
Planting calendar for Oswego, IL
Oswego, IL frost dates — last frost Apr 19, first frost Oct 23, zone 5b. whenisthelastfrost.com
Crop
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Start indoors: Jan 25 to Feb 8Transplant outside: Mar 22 to Apr 5
Start indoors: Feb 8 to Feb 22Transplant outside: May 3 to May 17
Start indoors: Feb 8 to Feb 22Transplant outside: May 3 to May 17
Start indoors: Feb 22 to Mar 8Transplant outside: Apr 26 to May 10
Start indoors: Feb 22 to Mar 8Transplant outside: Mar 29 to Apr 12Sow outdoors: Mar 22 to Apr 26Plant for fall: Aug 28 to Sep 25
Start indoors: Feb 22 to Mar 8Transplant outside: Mar 22 to Apr 5Sow outdoors: Mar 22 to Apr 5Plant for fall: Aug 14 to Sep 4
Start indoors: Feb 22 to Mar 8Transplant outside: Apr 5 to Apr 19Plant for fall: Jul 17 to Aug 7
Start indoors: Feb 22 to Mar 8Transplant outside: Mar 29 to Apr 12Plant for fall: Jul 17 to Aug 7
Start indoors: Feb 22 to Mar 8Transplant outside: Apr 5 to Apr 19Plant for fall: Jul 17 to Aug 7
Start indoors: Mar 8 to Mar 22Transplant outside: May 10 to May 24Sow outdoors: May 10 to May 24
Start indoors: Mar 8 to Mar 22Transplant outside: Apr 26 to May 10
Sow outdoors: Mar 8 to Mar 29Plant for fall: Jul 31 to Aug 21
Sow outdoors: Mar 8 to Mar 29Plant for fall: Aug 28 to Sep 18
Sow outdoors: Mar 15 to Apr 26Plant for fall: Sep 11 to Oct 2
Start indoors: Mar 22 to Mar 29Transplant outside: May 3 to May 10Sow outdoors: Apr 26 to May 10Plant for fall: Aug 7 to Aug 21
Start indoors: Mar 22 to Mar 29Sow outdoors: Apr 26 to May 10Plant for fall: Aug 14 to Aug 28
Start indoors: Mar 22 to Mar 29Sow outdoors: Apr 26 to May 10
Start indoors: Mar 22 to Mar 29Transplant outside: May 3 to May 17
Sow outdoors: Mar 29 to Apr 26Plant for fall: Jul 31 to Aug 14
Sow outdoors: Mar 29 to Apr 26Plant for fall: Aug 14 to Aug 28
Sow outdoors: Mar 29 to Apr 19
Sow outdoors: Apr 5 to May 3Plant for fall: Aug 14 to Aug 28
Sow outdoors: Apr 5 to Apr 26Plant for fall: Aug 28 to Sep 18
Sow outdoors: Apr 26 to May 17Plant for fall: Aug 7 to Aug 21
Sow outdoors: Apr 26 to May 10
Transplant outside: May 3 to May 24
Plant for fall: Oct 9 to Nov 13
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Oswego, IL
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Jan 25 – Feb 8 | Mar 22 – Apr 5 | — | — |
| Peppers | Feb 8 – Feb 22 | May 3 – May 17 | — | — |
| Eggplant | Feb 8 – Feb 22 | May 3 – May 17 | — | — |
| Tomatoes | Feb 22 – Mar 8 | Apr 26 – May 10 | — | — |
| Lettuce | Feb 22 – Mar 8 | Mar 29 – Apr 12 | Mar 22 – Apr 26 | Aug 28 – Sep 25 |
| Kale | Feb 22 – Mar 8 | Mar 22 – Apr 5 | Mar 22 – Apr 5 | Aug 14 – Sep 4 |
| Broccoli | Feb 22 – Mar 8 | Apr 5 – Apr 19 | — | Jul 17 – Aug 7 |
| Cabbage | Feb 22 – Mar 8 | Mar 29 – Apr 12 | — | Jul 17 – Aug 7 |
| Cauliflower | Feb 22 – Mar 8 | Apr 5 – Apr 19 | — | Jul 17 – Aug 7 |
| Okra | Mar 8 – Mar 22 | May 10 – May 24 | May 10 – May 24 | — |
| Basil | Mar 8 – Mar 22 | Apr 26 – May 10 | — | — |
| Peas | — | — | Mar 8 – Mar 29 | Jul 31 – Aug 21 |
| Spinach | — | — | Mar 8 – Mar 29 | Aug 28 – Sep 18 |
| Radishes | — | — | Mar 15 – Apr 26 | Sep 11 – Oct 2 |
| Cucumbers | Mar 22 – Mar 29 | May 3 – May 10 | Apr 26 – May 10 | Aug 7 – Aug 21 |
| Zucchini & Summer Squash | Mar 22 – Mar 29 | — | Apr 26 – May 10 | Aug 14 – Aug 28 |
| Winter Squash & Pumpkins | Mar 22 – Mar 29 | — | Apr 26 – May 10 | — |
| Melons & Watermelon | Mar 22 – Mar 29 | May 3 – May 17 | — | — |
| Carrots | — | — | Mar 29 – Apr 26 | Jul 31 – Aug 14 |
| Beets | — | — | Mar 29 – Apr 26 | Aug 14 – Aug 28 |
| Potatoes | — | — | Mar 29 – Apr 19 | — |
| Swiss Chard | — | — | Apr 5 – May 3 | Aug 14 – Aug 28 |
| Cilantro | — | — | Apr 5 – Apr 26 | Aug 28 – Sep 18 |
| Green Beans | — | — | Apr 26 – May 17 | Aug 7 – Aug 21 |
| Sweet Corn | — | — | Apr 26 – May 10 | — |
| Sweet Potatoes | — | May 3 – May 24 | — | — |
| Garlic | — | — | — | Oct 9 – Nov 13 |
Dates come from the median frost dates and common extension-service timing. Adjust for your soil temperature, microclimate and the varieties you grow.
About these dates
Based on 1991–2020 NOAA climate normals for the Aurora, IL weather station, 11 km away (elevation 659 ft (201 m)).
Frost dates near Oswego
- Montgomery Apr 19 · Oct 23
- Bristol Apr 28 · Oct 13
- Yorkville Apr 28 · Oct 13
- Aurora Apr 19 · Oct 23
- Sugar Grove Apr 28 · Oct 13
- Eola Apr 19 · Oct 23
- North Aurora Apr 19 · Oct 23
- Plainfield Apr 20 · Oct 22
- Mooseheart Apr 19 · Oct 23
- Plano Apr 28 · Oct 13
Frequently asked questions
When is the last frost in Oswego, IL?
The median last spring frost in Oswego, IL is April 19. There is still about a 10% chance of frost after May 4, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Oswego, IL?
The median first fall frost is October 23, with about a 10% chance of frost before October 9.
How long is the growing season in Oswego, IL?
About 187 days between the median last spring frost and first fall frost.
What planting zone is Oswego, IL?
Oswego, IL is in USDA hardiness zone 5b.