Frost dates for 50565Marathon, IA
The average last spring frost in Marathon is April 30 and the average first fall frost is October 5, giving a typical growing season of about 159 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 30
- Average first fall frost
- Oct 5
- Growing season
- 159 days
Safer after May 11 (1-in-10 risk)
Possible by Sep 22 (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 26 · May 8 · May 20 | Sep 15 · Sep 27 · Oct 9 | 141 days | 100% |
| Frost / freeze (32°F) | Apr 14 · Apr 30 · May 11 | Sep 22 · Oct 5 · Oct 21 | 159 days | 100% |
| Hard freeze (28°F) | Apr 4 · Apr 18 · May 2 | Oct 1 · Oct 18 · Oct 31 | 180 days | 100% |
Planting calendar for Marathon
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 15 |
| 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 25 |
| Summer squash | Sow outdoors | May 16 – Jun 30 |
| Winter squash & pumpkins | Sow outdoors | May 30 – Jun 30 |
| Snap beans | Sow outdoors | May 16 – Jul 18 |
| Sweet corn | Sow outdoors | May 16 – Jun 15 |
| 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 5 – Jun 15 |
| Broccoli | Transplant outdoors (fall) | Jul 5 – Jul 16 |
| Cabbage | Start seeds indoors (spring) | Mar 2 – Mar 30 |
| Cabbage | Transplant outdoors (spring) | Mar 30 – Apr 30 |
| Cabbage | Start seeds indoors (fall) | May 26 – Jun 25 |
| Cabbage | Transplant outdoors (fall) | Jun 25 – Jul 26 |
| Leaf lettuce | Sow outdoors (spring) | Mar 30 – Jun 15 |
| Leaf lettuce | Sow outdoors (fall) | Jun 25 – Aug 11 |
| Spinach | Sow outdoors (spring) | Mar 23 – May 6 |
| Spinach | Sow outdoors (fall) | Jul 12 – Aug 16 |
| Radishes | Sow outdoors (spring) | Mar 30 – May 20 |
| Radishes | Sow outdoors (fall) | Jun 25 – Aug 26 |
| Kale | Sow outdoors (spring) | Apr 16 – May 6 |
| Kale | Sow outdoors (fall) | Jun 18 – Jul 26 |
| Carrots | Sow outdoors (spring) | Apr 30 – Jun 15 |
| Carrots | Sow outdoors (fall) | May 26 – Jul 11 |
| Garlic | Plant outdoors (fall) | Sep 25 – Oct 26 |
Where these dates come from
ZIP code 50565 is matched to the NOAA station Sioux Rapids 4 E, IA, 7.5 km away, at 1,420 ft elevation (29 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Sioux Rapids 4 E, IA (used) | 1,420 ft | Apr 30 | Oct 5 |
| Storm Lake, IA | 1,442 ft | Apr 25 | Oct 13 |
| Pocahontas, IA | 1,212 ft | Apr 26 | Oct 7 |
| Emmetsburg, IA | 1,225 ft | Apr 27 | Oct 7 |
Frost dates near Marathon
- Albert City, IA 50510 · last Apr 30, first Oct 5
- Webb, IA 51366 · last Apr 30, first Oct 5
- Laurens, IA 50554 · last Apr 26, first Oct 7
- Sioux Rapids, IA 50585 · last Apr 30, first Oct 5
- Rembrandt, IA 50576 · last Apr 30, first Oct 5
- Gillett Grove, IA 51341 · last Apr 30, first Oct 5
- Curlew, IA 50527 · last Apr 27, first Oct 7
- Greenville, IA 51343 · last Apr 30, first Oct 5
Frequently asked questions
- When is the last frost in Marathon, IA?
- For ZIP code 50565, the average last spring frost (32°F) is April 30, based on NOAA 1991-2020 climate normals for the Sioux Rapids 4 E, IA weather station. There is a 1-in-10 chance of a frost after May 11.
- When is the first frost in Marathon, IA?
- The average first fall frost (32°F) is October 5. There is a 1-in-10 chance of frost by September 22, so tender plants are at risk from that point on.
- How long is the growing season in 50565?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 159 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.