When to plant in O'Fallon, MO
USDA Zone 6bO'Fallon, Missouri frost dates, USDA zone, and a full-year planting calendar, drawn from the nearest NOAA station and tuned to the local season.
Zone 6b means O'Fallon sees real winter cold, but a good range of perennials survive; the frost dates above govern when annual vegetables go out.
Frost probability
WELDON SPRING NWS · 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 WELDON SPRING NWS.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | May 6 | Apr 22 | Apr 8 | Oct 1 | Oct 16 | Oct 28 |
| 32°F | Apr 26 | Apr 10 | Mar 26 | Oct 12 | Oct 26 | Nov 8 |
| 28°F | Apr 15 | Mar 31 | Mar 12 | Oct 22 | Nov 5 | Nov 22 |
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 15 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, MO?
On average, the last spring frost in O'Fallon is around April 10 (50% probability at 32°F, from 1991–2020 NOAA normals). Wait until after this date to set out tender plants like tomatoes and peppers.
When is the first fall frost in O'Fallon, MO?
In O'Fallon, the first 32°F freeze of fall lands around October 26 on average. Time your last harvests and any season-extension cover before it.
What hardiness zone is O'Fallon in?
O'Fallon is in USDA hardiness zone 6b. In zone 6b, winters are moderate — most common vegetables grow well in season.
How long is the growing season in O'Fallon?
There are roughly 199 frost-free days in O'Fallon (a moderate growing season), running from the average last frost around April 10 to the first fall frost near October 26.
When should I plant tomatoes in O'Fallon?
In O'Fallon, start tomato seeds indoors around February 13–February 27, then transplant seedlings outdoors around April 17 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- Dardenne Prairie · 4 km
- Lake St. Louis · 6 km
- St. Peters · 10 km
- Wentzville · 14 km
- St. Charles · 18 km
- Chesterfield · 18 km
- Maryland Heights · 23 km
- Wildwood · 23 km
Frost dates recorded at WELDON SPRING NWS, 10 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, MO — Frost Dates & Zone 6b." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USC00238805. Retrieved from https://blissgarden.com/missouri/ofallon.