O Fallon, IL frost dates
Last spring frostApr 12median date
First fall frostOct 20median date
Growing season191 daysfrost-free
Hardiness zone7aZone 7a
How O Fallon compares
- In 8 years out of 10, the last spring frost in O Fallon falls between March 28 and April 28, a 31-day window. The first fall frost falls between October 3 and November 1.
- The median last frost is 5 days earlier than the Illinois median of Apr 17.
- Its 191-day growing season is longer than 62% of the 1,287 Illinois places with a regular frost season (state median 187 days).
- The last frost is 4 days earlier than the zone 7a median of Apr 16. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 7a chart.
- The weather station records an average of 93 nights a year at or below 32°F.
- Compared with Florissant, MO, 44 km away, the last frost here is 10 days later than there and the growing season is 25 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | March 28 |
| 50% (median) | April 12 |
| 10% (safe for tender plants) | April 28 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | October 3 |
| 50% (median) | October 20 |
| 90% (late) | November 1 |
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 O Fallon, IL
O Fallon, IL frost dates — last frost Apr 12, first frost Oct 20, zone 7a. whenisthelastfrost.com
Crop
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Start indoors: Jan 18 to Feb 1Transplant outside: Mar 15 to Mar 29
Start indoors: Feb 1 to Feb 15Transplant outside: Apr 26 to May 10
Start indoors: Feb 1 to Feb 15Transplant outside: Apr 26 to May 10
Start indoors: Feb 15 to Mar 1Transplant outside: Apr 19 to May 3
Start indoors: Feb 15 to Mar 1Transplant outside: Mar 22 to Apr 5Sow outdoors: Mar 15 to Apr 19Plant for fall: Aug 25 to Sep 22
Start indoors: Feb 15 to Mar 1Transplant outside: Mar 15 to Mar 29Sow outdoors: Mar 15 to Mar 29Plant for fall: Aug 11 to Sep 1
Start indoors: Feb 15 to Mar 1Transplant outside: Mar 29 to Apr 12Plant for fall: Jul 14 to Aug 4
Start indoors: Feb 15 to Mar 1Transplant outside: Mar 22 to Apr 5Plant for fall: Jul 14 to Aug 4
Start indoors: Feb 15 to Mar 1Transplant outside: Mar 29 to Apr 12Plant for fall: Jul 14 to Aug 4
Start indoors: Mar 1 to Mar 15Transplant outside: May 3 to May 17Sow outdoors: May 3 to May 17
Start indoors: Mar 1 to Mar 15Transplant outside: Apr 19 to May 3
Sow outdoors: Mar 1 to Mar 22Plant for fall: Jul 28 to Aug 18
Sow outdoors: Mar 1 to Mar 22Plant for fall: Aug 25 to Sep 15
Sow outdoors: Mar 8 to Apr 19Plant for fall: Sep 8 to Sep 29
Start indoors: Mar 15 to Mar 22Transplant outside: Apr 26 to May 3Sow outdoors: Apr 19 to May 3Plant for fall: Aug 4 to Aug 18
Start indoors: Mar 15 to Mar 22Sow outdoors: Apr 19 to May 3Plant for fall: Aug 11 to Aug 25
Start indoors: Mar 15 to Mar 22Sow outdoors: Apr 19 to May 3
Start indoors: Mar 15 to Mar 22Transplant outside: Apr 26 to May 10
Sow outdoors: Mar 22 to Apr 19Plant for fall: Jul 28 to Aug 11
Sow outdoors: Mar 22 to Apr 19Plant for fall: Aug 11 to Aug 25
Sow outdoors: Mar 22 to Apr 12
Sow outdoors: Mar 29 to Apr 26Plant for fall: Aug 11 to Aug 25
Sow outdoors: Mar 29 to Apr 19Plant for fall: Aug 25 to Sep 15
Sow outdoors: Apr 19 to May 10Plant for fall: Aug 4 to Aug 18
Sow outdoors: Apr 19 to May 3
Transplant outside: Apr 26 to May 17
Plant for fall: Oct 6 to Nov 10
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in O Fallon, IL
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Jan 18 – Feb 1 | Mar 15 – Mar 29 | — | — |
| Peppers | Feb 1 – Feb 15 | Apr 26 – May 10 | — | — |
| Eggplant | Feb 1 – Feb 15 | Apr 26 – May 10 | — | — |
| Tomatoes | Feb 15 – Mar 1 | Apr 19 – May 3 | — | — |
| Lettuce | Feb 15 – Mar 1 | Mar 22 – Apr 5 | Mar 15 – Apr 19 | Aug 25 – Sep 22 |
| Kale | Feb 15 – Mar 1 | Mar 15 – Mar 29 | Mar 15 – Mar 29 | Aug 11 – Sep 1 |
| Broccoli | Feb 15 – Mar 1 | Mar 29 – Apr 12 | — | Jul 14 – Aug 4 |
| Cabbage | Feb 15 – Mar 1 | Mar 22 – Apr 5 | — | Jul 14 – Aug 4 |
| Cauliflower | Feb 15 – Mar 1 | Mar 29 – Apr 12 | — | Jul 14 – Aug 4 |
| Okra | Mar 1 – Mar 15 | May 3 – May 17 | May 3 – May 17 | — |
| Basil | Mar 1 – Mar 15 | Apr 19 – May 3 | — | — |
| Peas | — | — | Mar 1 – Mar 22 | Jul 28 – Aug 18 |
| Spinach | — | — | Mar 1 – Mar 22 | Aug 25 – Sep 15 |
| Radishes | — | — | Mar 8 – Apr 19 | Sep 8 – Sep 29 |
| Cucumbers | Mar 15 – Mar 22 | Apr 26 – May 3 | Apr 19 – May 3 | Aug 4 – Aug 18 |
| Zucchini & Summer Squash | Mar 15 – Mar 22 | — | Apr 19 – May 3 | Aug 11 – Aug 25 |
| Winter Squash & Pumpkins | Mar 15 – Mar 22 | — | Apr 19 – May 3 | — |
| Melons & Watermelon | Mar 15 – Mar 22 | Apr 26 – May 10 | — | — |
| Carrots | — | — | Mar 22 – Apr 19 | Jul 28 – Aug 11 |
| Beets | — | — | Mar 22 – Apr 19 | Aug 11 – Aug 25 |
| Potatoes | — | — | Mar 22 – Apr 12 | — |
| Swiss Chard | — | — | Mar 29 – Apr 26 | Aug 11 – Aug 25 |
| Cilantro | — | — | Mar 29 – Apr 19 | Aug 25 – Sep 15 |
| Green Beans | — | — | Apr 19 – May 10 | Aug 4 – Aug 18 |
| Sweet Corn | — | — | Apr 19 – May 3 | — |
| Sweet Potatoes | — | Apr 26 – May 17 | — | — |
| Garlic | — | — | — | Oct 6 – Nov 10 |
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 Belleville Siu Rsch, IL weather station, 7 km away (elevation 449 ft (137 m)).
Frost dates near O Fallon
- Scott Air Force Base Apr 12 · Oct 20
- Lebanon Apr 12 · Oct 20
- Fairview Heights Apr 8 · Oct 26
- Belleville Apr 12 · Oct 20
- Caseyville Apr 8 · Oct 26
- Summerfield Apr 12 · Oct 20
- Mascoutah Apr 12 · Oct 20
- Collinsville Apr 8 · Oct 26
- Lovejoy Apr 12 · Oct 20
- Maryville Apr 8 · Oct 26
Frequently asked questions
When is the last frost in O Fallon, IL?
The median last spring frost in O Fallon, IL is April 12. There is still about a 10% chance of frost after April 28, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in O Fallon, IL?
The median first fall frost is October 20, with about a 10% chance of frost before October 3.
How long is the growing season in O Fallon, IL?
About 191 days between the median last spring frost and first fall frost.
What planting zone is O Fallon, IL?
O Fallon, IL is in USDA hardiness zone 7a.