Frost dates for 51249Sibley, IA
The average last spring frost in Sibley is May 5 and the average first fall frost is October 3, giving a typical growing season of about 152 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 5
- Average first fall frost
- Oct 3
- Growing season
- 152 days
Safer after May 17 (1-in-10 risk)
Possible by Sep 21 (1-in-10 risk)
Last frost typically in 190 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) | May 1 · May 12 · May 25 | Sep 11 · Sep 27 · Oct 8 | 136 days | 100% |
| Frost / freeze (32°F) | Apr 22 · May 5 · May 17 | Sep 21 · Oct 3 · Oct 17 | 152 days | 100% |
| Hard freeze (28°F) | Apr 11 · Apr 25 · May 8 | Sep 29 · Oct 13 · Oct 27 | 171 days | 100% |
Planting calendar for Sibley
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 4 – Jun 10 |
| Tomatoes | Transplant outdoors | May 21 – Jun 13 |
| Peppers | Start seeds indoors | Apr 4 – May 5 |
| Peppers | Transplant outdoors | Jun 4 – Jul 5 |
| Eggplant | Start seeds indoors | Apr 21 – May 20 |
| Eggplant | Transplant outdoors | Jun 4 – Jul 5 |
| Cucumbers | Sow outdoors | Jun 4 – Jun 23 |
| Summer squash | Sow outdoors | May 21 – Jul 5 |
| Winter squash & pumpkins | Sow outdoors | Jun 4 – Jul 5 |
| Snap beans | Sow outdoors | May 21 – Jul 16 |
| Sweet corn | Sow outdoors | May 21 – Jun 13 |
| Watermelon & cantaloupe | Sow outdoors | Jun 4 – Jul 5 |
| Okra | Sow outdoors | May 28 – Jun 20 |
| Peas | Sow outdoors (spring) | Apr 4 – May 20 |
| Potatoes | Plant outdoors (spring) | Apr 4 – Jun 4 |
| Onions | Start seeds indoors (spring) | Feb 21 – Mar 20 |
| Onions | Transplant outdoors (spring) | Apr 21 – May 20 |
| Broccoli | Start seeds indoors (spring) | Mar 17 – Apr 20 |
| Broccoli | Transplant outdoors (spring) | Apr 21 – May 20 |
| Broccoli | Start seeds indoors (fall) | Jun 3 – Jun 13 |
| Broccoli | Transplant outdoors (fall) | Jul 3 – Jul 14 |
| Cabbage | Start seeds indoors (spring) | Mar 7 – Apr 4 |
| Cabbage | Transplant outdoors (spring) | Apr 4 – May 5 |
| Cabbage | Start seeds indoors (fall) | May 24 – Jun 23 |
| Cabbage | Transplant outdoors (fall) | Jun 23 – Jul 24 |
| Leaf lettuce | Sow outdoors (spring) | Apr 4 – Jun 20 |
| Leaf lettuce | Sow outdoors (fall) | Jun 23 – Aug 9 |
| Spinach | Sow outdoors (spring) | Mar 28 – May 11 |
| Spinach | Sow outdoors (fall) | Jul 10 – Aug 14 |
| Radishes | Sow outdoors (spring) | Apr 4 – May 25 |
| Radishes | Sow outdoors (fall) | Jun 23 – Aug 24 |
| Kale | Sow outdoors (spring) | Apr 21 – May 11 |
| Kale | Sow outdoors (fall) | Jun 16 – Jul 24 |
| Carrots | Sow outdoors (spring) | May 5 – Jun 20 |
| Carrots | Sow outdoors (fall) | May 24 – Jul 9 |
| Garlic | Plant outdoors (fall) | Sep 23 – Oct 24 |
Where these dates come from
ZIP code 51249 is matched to the NOAA station Sibley, IA, 0.5 km away, at 1,529 ft elevation (10 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Sibley, IA (used) | 1,529 ft | May 5 | Oct 3 |
| Sanborn, IA | 1,551 ft | May 1 | Oct 7 |
| Sheldon, IA | 1,420 ft | May 5 | Sep 28 |
| Worthington 2 Nne, MN | 1,570 ft | May 3 | Oct 4 |
Frost dates near Sibley
- Ashton, IA 51232 · last May 5, first Oct 3
- Little Rock, IA 51243 · last May 5, first Oct 3
- Bigelow, MN 56117 · last May 3, first Oct 4
- Ocheyedan, IA 51354 · last Apr 30, first Oct 10
- Melvin, IA 51350 · last May 1, first Oct 7
- George, IA 51237 · last May 1, first Oct 4
- Matlock, IA 51244 · last May 5, first Sep 28
- Rushmore, MN 56168 · last May 3, first Oct 4
Frequently asked questions
- When is the last frost in Sibley, IA?
- For ZIP code 51249, the average last spring frost (32°F) is May 5, based on NOAA 1991-2020 climate normals for the Sibley, IA weather station. There is a 1-in-10 chance of a frost after May 17.
- When is the first frost in Sibley, IA?
- The average first fall frost (32°F) is October 3. There is a 1-in-10 chance of frost by September 21, so tender plants are at risk from that point on.
- How long is the growing season in 51249?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 152 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.