Frost Dates for O'Fallon, IL
In O'Fallon, IL, the average last spring frost is around Apr 12 and the average first fall frost around Oct 20, for a growing season of about 189 days. For frost-tender plants, wait until Apr 28, when the chance of frost drops to 10%.
Based on NOAA 1991–2020 records from the Belleville Siu Rsch, IL weather station, 7 miles away, elevation 450 ft. Frost can come earlier in low spots and valleys and later near cities and large lakes.
Frost probability by date
Chance of a 32°F frost after the spring date, or before the fall date.
| Chance | Last spring frost | First fall frost |
|---|---|---|
| 10% | Apr 28 | Oct 3 |
| 20% | Apr 22 | Oct 10 |
| 30% | Apr 19 | Oct 14 |
| 40% | Apr 15 | Oct 17 |
| 50% | Apr 12 | Oct 20 |
| 60% | Apr 8 | Oct 22 |
| 70% | Apr 5 | Oct 25 |
| 80% | Apr 2 | Oct 28 |
| 90% | Mar 28 | Nov 1 |
Light frost vs. hard freeze
Average (50%) dates for each temperature. Tender plants are damaged at 36°F; most hardy crops survive until 28°F.
| Temperature | Last in spring | First in fall |
|---|---|---|
| Light frost (36°F) | Apr 23 | Oct 9 |
| Frost / freeze (32°F) | Apr 12 | Oct 20 |
| Hard freeze (28°F) | Mar 31 | Oct 30 |
Planting calendar for O'Fallon
Transplant Apr 19 – May 3
Transplant Apr 26 – May 10
Transplant Apr 26 – May 10
Transplant Apr 19 – May 3
Sow or transplant Apr 19 – May 3
Sow or transplant Apr 19 – May 3
Sow or transplant Apr 26 – May 10
Sow or transplant Mar 15 – Mar 29
Fall sowing Aug 25 – Sep 22
Fall sowing Aug 25 – Sep 15
Fall sowing Aug 11 – Aug 25
Sow or transplant Mar 15 – Mar 29
Fall sowing Aug 11 – Sep 8
Transplant Mar 29 – Apr 12
Fall sowing Jul 28 – Aug 11
Transplant Mar 22 – Apr 5
Fall sowing Jul 28 – Aug 11
Fall sowing Jul 28 – Aug 11
Fall sowing Sep 8 – Sep 29
Fall sowing Aug 11 – Aug 25
Plant Mar 15 – Mar 29
Based on the average last frost (Apr 12) and first frost (Oct 20). The dashed lines mark those dates. Seed packets list days to maturity; adjust for your varieties.