Frost dates for 52161Ossian, IA
The average last spring frost in Ossian is May 1 and the average first fall frost is October 3, giving a typical growing season of about 153 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 1
- Average first fall frost
- Oct 3
- Growing season
- 153 days
Safer after May 14 (1-in-10 risk)
Possible by Sep 20 (1-in-10 risk)
Last frost typically in 186 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 28 · May 10 · May 23 | Sep 12 · Sep 24 · Oct 5 | 136 days | 100% |
| Frost / freeze (32°F) | Apr 18 · May 1 · May 14 | Sep 20 · Oct 3 · Oct 17 | 153 days | 100% |
| Hard freeze (28°F) | Apr 8 · Apr 22 · May 6 | Sep 29 · Oct 12 · Oct 28 | 174 days | 100% |
Planting calendar for Ossian
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 31 – Jun 6 |
| Tomatoes | Transplant outdoors | May 17 – Jun 13 |
| Peppers | Start seeds indoors | Mar 31 – May 1 |
| Peppers | Transplant outdoors | May 31 – Jul 1 |
| Eggplant | Start seeds indoors | Apr 17 – May 16 |
| Eggplant | Transplant outdoors | May 31 – Jul 1 |
| Cucumbers | Sow outdoors | May 31 – Jun 23 |
| Summer squash | Sow outdoors | May 17 – Jul 1 |
| Winter squash & pumpkins | Sow outdoors | May 31 – Jul 1 |
| Snap beans | Sow outdoors | May 17 – Jul 16 |
| Sweet corn | Sow outdoors | May 17 – Jun 13 |
| Watermelon & cantaloupe | Sow outdoors | May 31 – Jul 1 |
| Okra | Sow outdoors | May 24 – Jun 16 |
| Peas | Sow outdoors (spring) | Mar 31 – May 16 |
| Potatoes | Plant outdoors (spring) | Mar 31 – May 31 |
| Onions | Start seeds indoors (spring) | Feb 17 – Mar 16 |
| Onions | Transplant outdoors (spring) | Apr 17 – May 16 |
| Broccoli | Start seeds indoors (spring) | Mar 13 – Apr 16 |
| Broccoli | Transplant outdoors (spring) | Apr 17 – May 16 |
| Broccoli | Start seeds indoors (fall) | Jun 3 – Jun 13 |
| Broccoli | Transplant outdoors (fall) | Jul 3 – Jul 14 |
| Cabbage | Start seeds indoors (spring) | Mar 3 – Mar 31 |
| Cabbage | Transplant outdoors (spring) | Mar 31 – May 1 |
| Cabbage | Start seeds indoors (fall) | May 24 – Jun 23 |
| Cabbage | Transplant outdoors (fall) | Jun 23 – Jul 24 |
| Leaf lettuce | Sow outdoors (spring) | Mar 31 – Jun 16 |
| Leaf lettuce | Sow outdoors (fall) | Jun 23 – Aug 9 |
| Spinach | Sow outdoors (spring) | Mar 24 – May 7 |
| Spinach | Sow outdoors (fall) | Jul 10 – Aug 14 |
| Radishes | Sow outdoors (spring) | Mar 31 – May 21 |
| Radishes | Sow outdoors (fall) | Jun 23 – Aug 24 |
| Kale | Sow outdoors (spring) | Apr 17 – May 7 |
| Kale | Sow outdoors (fall) | Jun 16 – Jul 24 |
| Carrots | Sow outdoors (spring) | May 1 – Jun 16 |
| Carrots | Sow outdoors (fall) | May 24 – Jul 9 |
| Garlic | Plant outdoors (fall) | Sep 23 – Oct 24 |
Where these dates come from
ZIP code 52161 is matched to the NOAA station Postville, IA, 18.3 km away, at 1,165 ft elevation (69 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Postville, IA (used) | 1,165 ft | May 1 | Oct 3 |
| Decorah, IA | 860 ft | May 3 | Oct 7 |
| Fayette, IA | 1,145 ft | May 4 | Oct 4 |
| Waukon, IA | 1,275 ft | May 2 | Oct 11 |
Frost dates near Ossian
- Castalia, IA 52133 · last May 1, first Oct 3
- Fort Atkinson, IA 52144 · last May 3, first Oct 7
- Calmar, IA 52132 · last May 8, first Oct 1
- Saint Lucas, IA 52166 · last May 4, first Oct 4
- Spillville, IA 52168 · last May 3, first Oct 7
- Clermont, IA 52135 · last May 1, first Oct 3
- Decorah, IA 52101 · last May 3, first Oct 7
- West Union, IA 52175 · last May 4, first Oct 4
Frequently asked questions
- When is the last frost in Ossian, IA?
- For ZIP code 52161, the average last spring frost (32°F) is May 1, based on NOAA 1991-2020 climate normals for the Postville, IA weather station. There is a 1-in-10 chance of a frost after May 14.
- When is the first frost in Ossian, 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 52161?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 153 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.