Frost dates for 50240Saint Charles, IA
The average last spring frost in Saint Charles is April 30 and the average first fall frost is October 3, giving a typical growing season of about 157 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 30
- Average first fall frost
- Oct 3
- Growing season
- 157 days
Safer after May 11 (1-in-10 risk)
Possible by Sep 20 (1-in-10 risk)
Last frost typically in 185 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 27 · May 9 · May 22 | Sep 12 · Sep 26 · Oct 9 | 140 days | 100% |
| Frost / freeze (32°F) | Apr 17 · Apr 30 · May 11 | Sep 20 · Oct 3 · Oct 20 | 157 days | 100% |
| Hard freeze (28°F) | Apr 6 · Apr 20 · May 3 | Sep 29 · Oct 15 · Oct 28 | 178 days | 100% |
Planting calendar for Saint Charles
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 30 – Jun 5 |
| Tomatoes | Transplant outdoors | May 16 – Jun 13 |
| Peppers | Start seeds indoors | Mar 30 – Apr 30 |
| Peppers | Transplant outdoors | May 30 – Jun 30 |
| Eggplant | Start seeds indoors | Apr 16 – May 15 |
| Eggplant | Transplant outdoors | May 30 – Jun 30 |
| Cucumbers | Sow outdoors | May 30 – Jun 23 |
| Summer squash | Sow outdoors | May 16 – Jun 30 |
| Winter squash & pumpkins | Sow outdoors | May 30 – Jun 30 |
| Snap beans | Sow outdoors | May 16 – Jul 16 |
| Sweet corn | Sow outdoors | May 16 – Jun 13 |
| Watermelon & cantaloupe | Sow outdoors | May 30 – Jun 30 |
| Okra | Sow outdoors | May 23 – Jun 15 |
| Peas | Sow outdoors (spring) | Mar 30 – May 15 |
| Potatoes | Plant outdoors (spring) | Mar 30 – May 30 |
| Onions | Start seeds indoors (spring) | Feb 16 – Mar 15 |
| Onions | Transplant outdoors (spring) | Apr 16 – May 15 |
| Broccoli | Start seeds indoors (spring) | Mar 12 – Apr 15 |
| Broccoli | Transplant outdoors (spring) | Apr 16 – May 15 |
| Broccoli | Start seeds indoors (fall) | Jun 3 – Jun 13 |
| Broccoli | Transplant outdoors (fall) | Jul 3 – Jul 14 |
| Cabbage | Start seeds indoors (spring) | Mar 2 – Mar 30 |
| Cabbage | Transplant outdoors (spring) | Mar 30 – Apr 30 |
| Cabbage | Start seeds indoors (fall) | May 24 – Jun 23 |
| Cabbage | Transplant outdoors (fall) | Jun 23 – Jul 24 |
| Leaf lettuce | Sow outdoors (spring) | Mar 30 – Jun 15 |
| Leaf lettuce | Sow outdoors (fall) | Jun 23 – Aug 9 |
| Spinach | Sow outdoors (spring) | Mar 23 – May 6 |
| Spinach | Sow outdoors (fall) | Jul 10 – Aug 14 |
| Radishes | Sow outdoors (spring) | Mar 30 – May 20 |
| Radishes | Sow outdoors (fall) | Jun 23 – Aug 24 |
| Kale | Sow outdoors (spring) | Apr 16 – May 6 |
| Kale | Sow outdoors (fall) | Jun 16 – Jul 24 |
| Carrots | Sow outdoors (spring) | Apr 30 – Jun 15 |
| Carrots | Sow outdoors (fall) | May 24 – Jul 9 |
| Garlic | Plant outdoors (fall) | Sep 23 – Oct 24 |
Where these dates come from
ZIP code 50240 is matched to the NOAA station Winterset 1S, IA, 16.4 km away, at 1,100 ft elevation (90 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Winterset 1S, IA (used) | 1,100 ft | Apr 30 | Oct 3 |
| Indianola 2W, IA | 924 ft | Apr 24 | Oct 12 |
| Des Moines Intl Ap, IA | 957 ft | Apr 18 | Oct 20 |
| Osceola, IA | 1,028 ft | Apr 29 | Oct 9 |
Frost dates near Saint Charles
- Saint Marys, IA 50241 · last Apr 24, first Oct 12
- Patterson, IA 50218 · last Apr 24, first Oct 12
- Bevington, IA 50033 · last Apr 24, first Oct 12
- Truro, IA 50257 · last Apr 30, first Oct 3
- Martensdale, IA 50160 · last Apr 24, first Oct 12
- Prole, IA 50229 · last Apr 24, first Oct 12
- Peru, IA 50222 · last Apr 30, first Oct 3
- New Virginia, IA 50210 · last Apr 29, first Oct 9
Frequently asked questions
- When is the last frost in Saint Charles, IA?
- For ZIP code 50240, the average last spring frost (32°F) is April 30, based on NOAA 1991-2020 climate normals for the Winterset 1S, IA weather station. There is a 1-in-10 chance of a frost after May 11.
- When is the first frost in Saint Charles, IA?
- The average first fall frost (32°F) is October 3. There is a 1-in-10 chance of frost by September 20, so tender plants are at risk from that point on.
- How long is the growing season in 50240?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 157 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.