Frost dates for 62664Mason City, IL
The average last spring frost in Mason City is April 17 and the average first fall frost is October 18, giving a typical growing season of about 182 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 17
- Average first fall frost
- Oct 18
- Growing season
- 182 days
Safer after May 4 (1-in-10 risk)
Possible by Oct 4 (1-in-10 risk)
Last frost typically in 167 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 14 · Apr 28 · May 15 | Sep 23 · Oct 7 · Oct 20 | 162 days | 100% |
| Frost / freeze (32°F) | Apr 4 · Apr 17 · May 4 | Oct 4 · Oct 18 · Oct 30 | 182 days | 100% |
| Hard freeze (28°F) | Mar 22 · Apr 6 · Apr 20 | Oct 15 · Oct 29 · Nov 9 | 203 days | 100% |
Planting calendar for Mason City
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 17 – May 23 |
| Tomatoes | Transplant outdoors | May 3 – Jun 28 |
| Peppers | Start seeds indoors | Mar 17 – Apr 17 |
| Peppers | Transplant outdoors | May 17 – Jun 17 |
| Eggplant | Start seeds indoors | Apr 3 – May 2 |
| Eggplant | Transplant outdoors | May 17 – Jun 17 |
| Cucumbers | Sow outdoors | May 17 – Jul 8 |
| Summer squash | Sow outdoors | May 3 – Jun 17 |
| Winter squash & pumpkins | Sow outdoors | May 17 – Jun 17 |
| Snap beans | Sow outdoors | May 3 – Jul 31 |
| Sweet corn | Sow outdoors | May 3 – Jun 28 |
| Watermelon & cantaloupe | Sow outdoors | May 17 – Jun 17 |
| Okra | Sow outdoors | May 10 – Jun 2 |
| Peas | Sow outdoors (spring) | Mar 17 – May 2 |
| Potatoes | Plant outdoors (spring) | Mar 17 – May 17 |
| Onions | Start seeds indoors (spring) | Feb 3 – Mar 2 |
| Onions | Transplant outdoors (spring) | Apr 3 – May 2 |
| Broccoli | Start seeds indoors (spring) | Feb 27 – Apr 2 |
| Broccoli | Transplant outdoors (spring) | Apr 3 – May 2 |
| Broccoli | Start seeds indoors (fall) | Jun 18 – Jun 28 |
| Broccoli | Transplant outdoors (fall) | Jul 18 – Jul 29 |
| Cabbage | Start seeds indoors (spring) | Feb 17 – Mar 17 |
| Cabbage | Transplant outdoors (spring) | Mar 17 – Apr 17 |
| Cabbage | Start seeds indoors (fall) | Jun 8 – Jul 8 |
| Cabbage | Transplant outdoors (fall) | Jul 8 – Aug 8 |
| Leaf lettuce | Sow outdoors (spring) | Mar 17 – Jun 2 |
| Leaf lettuce | Sow outdoors (fall) | Jul 8 – Aug 24 |
| Spinach | Sow outdoors (spring) | Mar 10 – Apr 23 |
| Spinach | Sow outdoors (fall) | Jul 25 – Aug 29 |
| Radishes | Sow outdoors (spring) | Mar 17 – May 7 |
| Radishes | Sow outdoors (fall) | Jul 8 – Sep 8 |
| Kale | Sow outdoors (spring) | Apr 3 – Apr 23 |
| Kale | Sow outdoors (fall) | Jul 1 – Aug 8 |
| Carrots | Sow outdoors (spring) | Apr 17 – Jun 2 |
| Carrots | Sow outdoors (fall) | Jun 8 – Jul 24 |
| Garlic | Plant outdoors (fall) | Oct 8 – Nov 8 |
Where these dates come from
ZIP code 62664 is matched to the NOAA station Mason City 4Se, IL, 5.8 km away, at 600 ft elevation (23 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Mason City 4Se, IL (used) | 600 ft | Apr 17 | Oct 18 |
| Petersburg 1E, IL | 600 ft | Apr 13 | Oct 21 |
| Lincoln, IL | 583 ft | Apr 20 | Oct 16 |
| Athens 4Sw, IL | 594 ft | Apr 19 | Oct 19 |
Frost dates near Mason City
- San Jose, IL 62682 · last Apr 17, first Oct 18
- Greenview, IL 62642 · last Apr 17, first Oct 18
- New Holland, IL 62671 · last Apr 20, first Oct 16
- Middletown, IL 62666 · last Apr 20, first Oct 16
- Easton, IL 62633 · last Apr 17, first Oct 19
- Lincoln'S New Salem, IL 62659 · last Apr 13, first Oct 21
- Forest City, IL 61532 · last Apr 17, first Oct 19
- Hartsburg, IL 62643 · last Apr 20, first Oct 16
Frequently asked questions
- When is the last frost in Mason City, IL?
- For ZIP code 62664, the average last spring frost (32°F) is April 17, based on NOAA 1991-2020 climate normals for the Mason City 4Se, IL weather station. There is a 1-in-10 chance of a frost after May 4.
- When is the first frost in Mason City, IL?
- The average first fall frost (32°F) is October 18. There is a 1-in-10 chance of frost by October 4, so tender plants are at risk from that point on.
- How long is the growing season in 62664?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 182 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.