Last spring frost
Apr 30
Frost Dates for Charles City, IA
First fall frost
Oct 6
Growing season
157 days
Hardiness zone
5a
In an average year around Charles City, IA, the last spring frost (32°F) is about Apr 30 and the first fall frost is about Oct 6, giving roughly a 157-day growing season. To be safe most years, wait until Apr 15 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 22 | May 9 | Apr 27 |
| Freeze (32°F) | May 14 | Apr 30 | Apr 15 |
| Hard (28°F) | May 6 | Apr 21 | Apr 5 |
| Severe (24°F) | Apr 29 | Apr 9 | Mar 26 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 22 | May 18 | May 15 | May 12 | May 9 | May 7 | May 4 | May 1 | Apr 27 |
| 32°F | May 14 | May 10 | May 6 | May 3 | Apr 30 | Apr 28 | Apr 24 | Apr 20 | Apr 15 |
| 28°F | May 6 | May 1 | Apr 28 | Apr 24 | Apr 21 | Apr 17 | Apr 14 | Apr 10 | Apr 5 |
| 24°F | Apr 29 | Apr 22 | Apr 17 | Apr 13 | Apr 9 | Apr 7 | Apr 3 | Mar 31 | Mar 26 |
| 20°F | Apr 16 | Apr 10 | Apr 5 | Apr 2 | Mar 31 | Mar 28 | Mar 24 | Mar 20 | Mar 13 |
| 16°F | Apr 8 | Apr 2 | Mar 29 | Mar 25 | Mar 21 | Mar 18 | Mar 13 | Mar 10 | Mar 5 |
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 15 | Sep 27 | Oct 9 |
| Freeze (32°F) | Sep 21 | Oct 6 | Oct 19 |
| Hard (28°F) | Oct 3 | Oct 17 | Oct 29 |
| Severe (24°F) | Oct 12 | Oct 27 | Nov 9 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 15 | Sep 19 | Sep 22 | Sep 25 | Sep 27 | Sep 30 | Oct 3 | Oct 5 | Oct 9 |
| 32°F | Sep 21 | Sep 26 | Oct 1 | Oct 3 | Oct 6 | Oct 8 | Oct 11 | Oct 15 | Oct 19 |
| 28°F | Oct 3 | Oct 7 | Oct 10 | Oct 14 | Oct 17 | Oct 19 | Oct 22 | Oct 25 | Oct 29 |
| 24°F | Oct 12 | Oct 19 | Oct 21 | Oct 24 | Oct 27 | Oct 29 | Oct 31 | Nov 4 | Nov 9 |
| 20°F | Oct 24 | Oct 29 | Oct 31 | Nov 2 | Nov 5 | Nov 7 | Nov 10 | Nov 13 | Nov 18 |
| 16°F | Nov 2 | Nov 5 | Nov 8 | Nov 11 | Nov 14 | Nov 16 | Nov 20 | Nov 24 | Nov 29 |
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: Charles City, Ia, about 1.5 miles away@if(!empty($station['elevation_ft'])), at 993 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 Charles City, IA?
On average, the last spring frost (32°F) around Charles City, IA is about Apr 30. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 15.
When is the first frost in the fall?
The first fall frost around Charles City, IA typically arrives about Oct 6. 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 Apr 30 on average, or Apr 15 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 157 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 50616 Planting calendar → Iowa frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026