Frost dates for 63366O Fallon, MO
The average last spring frost in O Fallon is April 8 and the average first fall frost is October 29, giving a typical growing season of about 203 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 8
- Average first fall frost
- Oct 29
- Growing season
- 203 days
Safer after Apr 24 (1-in-10 risk)
Possible by Oct 16 (1-in-10 risk)
Last frost typically in 157 days
Frost risk by date
NOAA reports frost dates as probabilities. The middle date is the average (a 50% chance). For spring, the 10% date is a safer planting date: frost after it happens in about 1 year in 10. Light frost (36°F) can damage tender plants; a hard freeze (28°F) kills most annuals.
| Temperature | Last spring: 90% / 50% / 10% chance | First fall: 10% / 50% / 90% chance | Growing season (50%) | Years with at least one |
|---|---|---|---|---|
| Light frost (36°F) | Apr 5 · Apr 21 · May 5 | Oct 7 · Oct 19 · Oct 31 | 180 days | 100% |
| Frost / freeze (32°F) | Mar 23 · Apr 8 · Apr 24 | Oct 16 · Oct 29 · Nov 12 | 203 days | 100% |
| Hard freeze (28°F) | Mar 9 · Mar 30 · Apr 15 | Oct 29 · Nov 10 · Nov 28 | 225 days | 100% |
Planting calendar for O Fallon
Planting windows from the University of Maryland Extension calendar, shifted to your average frost dates. Use them as a starting point and adjust for seed packet instructions and local conditions.
| Crop | Task | Window |
|---|---|---|
| Tomatoes | Start seeds indoors | Mar 8 – May 14 |
| Tomatoes | Transplant outdoors | Apr 24 – Jul 9 |
| Peppers | Start seeds indoors | Mar 8 – Apr 8 |
| Peppers | Transplant outdoors | May 8 – Jun 8 |
| Eggplant | Start seeds indoors | Mar 25 – Apr 23 |
| Eggplant | Transplant outdoors | May 8 – Jun 8 |
| Cucumbers | Sow outdoors | May 8 – Jul 19 |
| Summer squash | Sow outdoors | Apr 24 – Jun 8 |
| Winter squash & pumpkins | Sow outdoors | May 8 – Jun 8 |
| Snap beans | Sow outdoors | Apr 24 – Aug 11 |
| Sweet corn | Sow outdoors | Apr 24 – Jul 9 |
| Watermelon & cantaloupe | Sow outdoors | May 8 – Jun 8 |
| Okra | Sow outdoors | May 1 – May 24 |
| Peas | Sow outdoors (spring) | Mar 8 – Apr 23 |
| Potatoes | Plant outdoors (spring) | Mar 8 – May 8 |
| Onions | Start seeds indoors (spring) | Jan 25 – Feb 21 |
| Onions | Transplant outdoors (spring) | Mar 25 – Apr 23 |
| Broccoli | Start seeds indoors (spring) | Feb 18 – Mar 24 |
| Broccoli | Transplant outdoors (spring) | Mar 25 – Apr 23 |
| Broccoli | Start seeds indoors (fall) | Jun 29 – Jul 9 |
| Broccoli | Transplant outdoors (fall) | Jul 29 – Aug 9 |
| Cabbage | Start seeds indoors (spring) | Feb 8 – Mar 8 |
| Cabbage | Transplant outdoors (spring) | Mar 8 – Apr 8 |
| Cabbage | Start seeds indoors (fall) | Jun 19 – Jul 19 |
| Cabbage | Transplant outdoors (fall) | Jul 19 – Aug 19 |
| Leaf lettuce | Sow outdoors (spring) | Mar 8 – May 24 |
| Leaf lettuce | Sow outdoors (fall) | Jul 19 – Sep 4 |
| Spinach | Sow outdoors (spring) | Mar 1 – Apr 14 |
| Spinach | Sow outdoors (fall) | Aug 5 – Sep 9 |
| Radishes | Sow outdoors (spring) | Mar 8 – Apr 28 |
| Radishes | Sow outdoors (fall) | Jul 19 – Sep 19 |
| Kale | Sow outdoors (spring) | Mar 25 – Apr 14 |
| Kale | Sow outdoors (fall) | Jul 12 – Aug 19 |
| Carrots | Sow outdoors (spring) | Apr 8 – May 24 |
| Carrots | Sow outdoors (fall) | Jun 19 – Aug 4 |
| Garlic | Plant outdoors (fall) | Oct 19 – Nov 19 |
Where these dates come from
ZIP code 63366 is matched to the NOAA station St Charles Elm Pt, MO, 19.9 km away, at 472 ft elevation (10 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| St Charles Elm Pt, MO (used) | 472 ft | Apr 8 | Oct 29 |
| St Peters 2 Se, MO | 575 ft | Apr 9 | Oct 26 |
| Weldon Spring Nws, MO | 610 ft | Apr 10 | Oct 26 |
| St Louis Sprt Of S L Ap, MO | 462 ft | Apr 12 | Oct 23 |
Frost dates near O Fallon
- Lake Saint Louis, MO 63367 · last Apr 10, first Oct 26
- O Fallon, MO 63368 · last Apr 10, first Oct 26
- Wentzville, MO 63385 · last Apr 10, first Oct 26
- Saint Peters, MO 63376 · last Apr 8, first Oct 29
- Cottleville, MO 63338 · last Apr 10, first Oct 26
- Old Monroe, MO 63369 · last Apr 20, first Oct 20
- Saint Charles, MO 63304 · last Apr 10, first Oct 26
- New Melle, MO 63365 · last Apr 10, first Oct 26
Frequently asked questions
- When is the last frost in O Fallon, MO?
- For ZIP code 63366, the average last spring frost (32°F) is April 8, based on NOAA 1991-2020 climate normals for the St Charles Elm Pt, MO weather station. There is a 1-in-10 chance of a frost after April 24.
- When is the first frost in O Fallon, MO?
- The average first fall frost (32°F) is October 29. There is a 1-in-10 chance of frost by October 16, so tender plants are at risk from that point on.
- How long is the growing season in 63366?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 203 days long.
- Are these frost dates a forecast?
- No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.