Frost dates for 50251Sully, IA
The average last spring frost in Sully is May 3 and the average first fall frost is October 6, giving a typical growing season of about 155 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 3
- Average first fall frost
- Oct 6
- Growing season
- 155 days
Safer after May 17 (1-in-10 risk)
Possible by Sep 22 (1-in-10 risk)
Last frost typically in 181 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 30 · May 13 · May 27 | Sep 15 · Sep 27 · Oct 10 | 136 days | 100% |
| Frost / freeze (32°F) | Apr 19 · May 3 · May 17 | Sep 22 · Oct 6 · Oct 20 | 155 days | 100% |
| Hard freeze (28°F) | Apr 9 · Apr 23 · May 9 | Oct 1 · Oct 17 · Oct 29 | 175 days | 100% |
Planting calendar for Sully
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 | Apr 2 – Jun 8 |
| Tomatoes | Transplant outdoors | May 19 – Jun 16 |
| Peppers | Start seeds indoors | Apr 2 – May 3 |
| Peppers | Transplant outdoors | Jun 2 – Jul 3 |
| Eggplant | Start seeds indoors | Apr 19 – May 18 |
| Eggplant | Transplant outdoors | Jun 2 – Jul 3 |
| Cucumbers | Sow outdoors | Jun 2 – Jun 26 |
| Summer squash | Sow outdoors | May 19 – Jul 3 |
| Winter squash & pumpkins | Sow outdoors | Jun 2 – Jul 3 |
| Snap beans | Sow outdoors | May 19 – Jul 19 |
| Sweet corn | Sow outdoors | May 19 – Jun 16 |
| Watermelon & cantaloupe | Sow outdoors | Jun 2 – Jul 3 |
| Okra | Sow outdoors | May 26 – Jun 18 |
| Peas | Sow outdoors (spring) | Apr 2 – May 18 |
| Potatoes | Plant outdoors (spring) | Apr 2 – Jun 2 |
| Onions | Start seeds indoors (spring) | Feb 19 – Mar 18 |
| Onions | Transplant outdoors (spring) | Apr 19 – May 18 |
| Broccoli | Start seeds indoors (spring) | Mar 15 – Apr 18 |
| Broccoli | Transplant outdoors (spring) | Apr 19 – May 18 |
| Broccoli | Start seeds indoors (fall) | Jun 6 – Jun 16 |
| Broccoli | Transplant outdoors (fall) | Jul 6 – Jul 17 |
| Cabbage | Start seeds indoors (spring) | Mar 5 – Apr 2 |
| Cabbage | Transplant outdoors (spring) | Apr 2 – May 3 |
| Cabbage | Start seeds indoors (fall) | May 27 – Jun 26 |
| Cabbage | Transplant outdoors (fall) | Jun 26 – Jul 27 |
| Leaf lettuce | Sow outdoors (spring) | Apr 2 – Jun 18 |
| Leaf lettuce | Sow outdoors (fall) | Jun 26 – Aug 12 |
| Spinach | Sow outdoors (spring) | Mar 26 – May 9 |
| Spinach | Sow outdoors (fall) | Jul 13 – Aug 17 |
| Radishes | Sow outdoors (spring) | Apr 2 – May 23 |
| Radishes | Sow outdoors (fall) | Jun 26 – Aug 27 |
| Kale | Sow outdoors (spring) | Apr 19 – May 9 |
| Kale | Sow outdoors (fall) | Jun 19 – Jul 27 |
| Carrots | Sow outdoors (spring) | May 3 – Jun 18 |
| Carrots | Sow outdoors (fall) | May 27 – Jul 12 |
| Garlic | Plant outdoors (fall) | Sep 26 – Oct 27 |
Where these dates come from
ZIP code 50251 is matched to the NOAA station Grinnell 3 Sw, IA, 18.1 km away, at 905 ft elevation (17 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Grinnell 3 Sw, IA (used) | 905 ft | May 3 | Oct 6 |
| Newton, IA | 960 ft | Apr 22 | Oct 17 |
| Oskaloosa, IA | 830 ft | Apr 21 | Oct 16 |
| Knoxville, IA | 895 ft | Apr 20 | Oct 19 |
Frost dates near Sully
- Lynnville, IA 50153 · last May 3, first Oct 6
- Killduff, IA 50137 · last Apr 22, first Oct 17
- Searsboro, IA 50242 · last May 3, first Oct 6
- Reasnor, IA 50232 · last Apr 22, first Oct 17
- Kellogg, IA 50135 · last Apr 22, first Oct 17
- New Sharon, IA 50207 · last Apr 21, first Oct 16
- Pella, IA 50219 · last Apr 20, first Oct 19
- Grinnell, IA 50112 · last May 3, first Oct 6
Frequently asked questions
- When is the last frost in Sully, IA?
- For ZIP code 50251, the average last spring frost (32°F) is May 3, based on NOAA 1991-2020 climate normals for the Grinnell 3 Sw, IA weather station. There is a 1-in-10 chance of a frost after May 17.
- When is the first frost in Sully, IA?
- The average first fall frost (32°F) is October 6. 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 50251?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 155 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.