When to plant in O'Fallon, IL
USDA Zone 7aEverything below — frost dates, hardiness zone, and what to plant when in O'Fallon, Illinois — is derived from the closest NOAA station with complete climate normals.
Zone 7a means many perennials and even some tender shrubs overwinter in O'Fallon, while your frost dates still decide when annuals go out.
The average first fall frost in O'Fallon is now 5 days later than in the 1981–2010 normals. See how frost dates are shifting nationwide →
Frost probability
BELLEVILLE SIU RSCH · 1991–2020The date the last spring and first fall frost occur, by threshold and probability. A 90% date is later in spring — and earlier in fall — than a 10% date; the 50% · 32°F row is what most gardeners plan around. These are O'Fallon’s own odds, recorded at BELLEVILLE SIU RSCH.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | May 8 | Apr 23 | Apr 10 | Sep 27 | Oct 9 | Oct 23 |
| 32°F | Apr 28 | Apr 12 | Mar 28 | Oct 3 | Oct 20 | Nov 1 |
| 28°F | Apr 16 | Mar 31 | Mar 14 | Oct 15 | Oct 30 | Nov 15 |
Download this table as CSV ↓ — every threshold and probability, plus this city’s planting-window dates.
What to plant now
TODAY · JULY 19Full-year planting calendar
Each bar is the exact window to take a planting action in O'Fallon, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 25 km · complete 32°F normalsWhen stations disagree by more than a few days, that spread is real microclimate variation — elevation, water, urban heat. Judge which station best matches your own yard.
O'Fallon planting FAQ
When is the last spring frost in O'Fallon, IL?
Plan for the last spring frost in O'Fallon around April 12 (the date it has a 50% chance of a 32°F freeze). Anything frost-sensitive should go out after it.
When is the first fall frost in O'Fallon, IL?
Expect O'Fallon's first fall frost near October 20 — a 50% chance of 32°F by that date. Bring in or cover tender crops ahead of it.
What hardiness zone is O'Fallon in?
O'Fallon is in USDA hardiness zone 7a. In zone 7a, winters are moderate — most common vegetables grow well in season.
How long is the growing season in O'Fallon?
There are roughly 191 frost-free days in O'Fallon (a moderate growing season), running from the average last frost around April 12 to the first fall frost near October 20.
When should I plant tomatoes in O'Fallon?
In O'Fallon, start tomato seeds indoors around February 15–March 1, then transplant seedlings outdoors around April 19 once the danger of frost has passed.
Never miss a window in O'Fallon
An email when it’s time to start seeds, transplant, and sow — timed to O'Fallon’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reach- Shiloh · 5 km
- Fairview Heights · 8 km
- Swansea · 8 km
- Belleville · 11 km
- Collinsville · 12 km
- Troy · 14 km
- Glen Carbon · 19 km
- East St. Louis · 19 km
Frost dates recorded at BELLEVILLE SIU RSCH, 11 km from the city center · 1991–2020 NOAA climate normals · zone from the USDA/PRISM 2023 map. How we compute this.
BlissGarden. "When to Plant in O'Fallon, IL — Frost Dates & Zone 7a." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USW00013802. Retrieved from https://blissgarden.com/illinois/ofallon.