Last spring frost
May 4
Frost Dates for Swea City, IA
First fall frost
Oct 1
Growing season
150 days
Hardiness zone
5a
In an average year around Swea City, IA, the last spring frost (32°F) is about May 4 and the first fall frost is about Oct 1, giving roughly a 150-day growing season. To be safe most years, wait until Apr 21 before setting out tender plants.
Last spring frost
Dates the last frost of spring typically ends. Plant tender crops after the risk has passed for your comfort level.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Light (36°F) | May 24 | May 11 | May 1 |
| Freeze (32°F) | May 14 | May 4 | Apr 21 |
| Hard (28°F) | May 6 | Apr 25 | Apr 9 |
| Severe (24°F) | Apr 29 | Apr 14 | Mar 31 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 24 | May 19 | May 16 | May 14 | May 11 | May 9 | May 7 | May 4 | May 1 |
| 32°F | May 14 | May 10 | May 8 | May 6 | May 4 | May 2 | Apr 30 | Apr 26 | Apr 21 |
| 28°F | May 6 | May 3 | Apr 30 | Apr 28 | Apr 25 | Apr 22 | Apr 18 | Apr 14 | Apr 9 |
| 24°F | Apr 29 | Apr 24 | Apr 21 | Apr 17 | Apr 14 | Apr 11 | Apr 7 | Apr 4 | Mar 31 |
| 20°F | Apr 22 | Apr 15 | Apr 11 | Apr 8 | Apr 5 | Apr 2 | Mar 30 | Mar 25 | Mar 19 |
| 16°F | Apr 12 | Apr 7 | Apr 3 | Mar 31 | Mar 27 | Mar 23 | Mar 20 | Mar 16 | Mar 11 |
First fall frost
Dates the first frost of fall typically arrives. Count back by a crop's days-to-maturity to know your planting cutoff.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Light (36°F) | Sep 11 | Sep 23 | Oct 6 |
| Freeze (32°F) | Sep 18 | Oct 1 | Oct 15 |
| Hard (28°F) | Sep 26 | Oct 10 | Oct 24 |
| Severe (24°F) | Oct 7 | Oct 22 | Nov 4 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 11 | Sep 16 | Sep 18 | Sep 20 | Sep 23 | Sep 25 | Sep 28 | Oct 1 | Oct 6 |
| 32°F | Sep 18 | Sep 23 | Sep 26 | Sep 28 | Oct 1 | Oct 3 | Oct 6 | Oct 10 | Oct 15 |
| 28°F | Sep 26 | Sep 30 | Oct 3 | Oct 7 | Oct 10 | Oct 12 | Oct 16 | Oct 20 | Oct 24 |
| 24°F | Oct 7 | Oct 12 | Oct 16 | Oct 19 | Oct 22 | Oct 24 | Oct 27 | Oct 31 | Nov 4 |
| 20°F | Oct 18 | Oct 22 | Oct 25 | Oct 29 | Oct 31 | Nov 2 | Nov 5 | Nov 9 | Nov 14 |
| 16°F | Oct 27 | Nov 1 | Nov 2 | Nov 5 | Nov 8 | Nov 10 | Nov 14 | Nov 18 | Nov 24 |
Growing season is measured at 32°F with about 50% probability. Hardiness zone from the 2023 USDA map; frost normals from NOAA 1991-2020.
Where this data comes from
@endif These dates are computed from the nearest official weather station with long-term records: Swea City 5N, Ia, about 3.3 miles away@if(!empty($station['elevation_ft'])), at 1,180 ft elevation. The further the station and the greater the elevation difference from your yard, the more your local frost timing can vary.
How we calculate these dates
Frost and freeze dates come from the NOAA 1991–2020 U.S. Climate Normals, the National Oceanic and Atmospheric Administration's 30-year averages for each weather station. A date shown at the 50% level is the median: in half of years the frost falls on or before it. The 10% and 90% columns show the early and late ends of the range, so you can plant on the odds you're comfortable with. These are long-term averages, not a forecast for this year - always check your local outlook before planting.
Source: NOAA National Centers for Environmental Information, 1991–2020 Climate Normals (public domain). Harman is not affiliated with or endorsed by NOAA.
Frequently asked questions
When is the last frost in Swea City, IA?
On average, the last spring frost (32°F) around Swea City, IA is about May 4. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 21.
When is the first frost in the fall?
The first fall frost around Swea City, IA typically arrives about Oct 1. Count back by a crop's days to maturity to find the latest date you can plant it.
When can I plant tomatoes and other tender crops?
Tender crops like tomatoes, peppers and basil are damaged by frost, so wait until the last spring frost has passed - around May 4 on average, or Apr 21 to be safe most years.
How long is the growing season here?
The frost-free growing season (between the last spring and first fall 32°F frost) is about 150 days in a typical year.
Are these dates a forecast for this year?
No. They are 30-year averages from the NOAA 1991–2020 Climate Normals, not a prediction for the current year. Use them for planning and always check your local weather forecast before planting or protecting crops.
Local weather for 50590 Planting calendar → Iowa frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026