Last spring frost
Apr 30
Frost Dates for Truro, IA
First fall frost
Oct 3
Growing season
157 days
Hardiness zone
5b
In an average year around Truro, IA, the last spring frost (32°F) is about Apr 30 and the first fall frost is about Oct 3, giving roughly a 157-day growing season. To be safe most years, wait until Apr 17 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 11 | Apr 30 | Apr 17 |
| Hard (28°F) | May 3 | Apr 20 | Apr 6 |
| Severe (24°F) | Apr 24 | Apr 10 | Mar 27 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 22 | May 18 | May 14 | May 11 | May 9 | May 7 | May 4 | May 1 | Apr 27 |
| 32°F | May 11 | May 7 | May 4 | May 2 | Apr 30 | Apr 28 | Apr 24 | Apr 21 | Apr 17 |
| 28°F | May 3 | Apr 30 | Apr 26 | Apr 23 | Apr 20 | Apr 17 | Apr 15 | Apr 11 | Apr 6 |
| 24°F | Apr 24 | Apr 20 | Apr 17 | Apr 13 | Apr 10 | Apr 8 | Apr 5 | Apr 1 | Mar 27 |
| 20°F | Apr 17 | Apr 11 | Apr 7 | Apr 4 | Apr 2 | Mar 31 | Mar 26 | Mar 21 | Mar 14 |
| 16°F | Apr 8 | Apr 2 | Mar 31 | Mar 27 | Mar 23 | Mar 19 | Mar 14 | Mar 10 | Mar 4 |
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 12 | Sep 26 | Oct 9 |
| Freeze (32°F) | Sep 20 | Oct 3 | Oct 20 |
| Hard (28°F) | Sep 29 | Oct 15 | Oct 28 |
| Severe (24°F) | Oct 10 | Oct 26 | Nov 7 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 12 | Sep 17 | Sep 20 | Sep 23 | Sep 26 | Sep 29 | Oct 1 | Oct 4 | Oct 9 |
| 32°F | Sep 20 | Sep 25 | Sep 28 | Oct 1 | Oct 3 | Oct 6 | Oct 11 | Oct 14 | Oct 20 |
| 28°F | Sep 29 | Oct 3 | Oct 8 | Oct 12 | Oct 15 | Oct 18 | Oct 22 | Oct 25 | Oct 28 |
| 24°F | Oct 10 | Oct 16 | Oct 20 | Oct 24 | Oct 26 | Oct 29 | Oct 31 | Nov 2 | Nov 7 |
| 20°F | Oct 20 | Oct 26 | Oct 30 | Nov 1 | Nov 3 | Nov 5 | Nov 9 | Nov 13 | Nov 19 |
| 16°F | Oct 30 | Nov 2 | Nov 6 | Nov 9 | Nov 12 | Nov 15 | Nov 19 | Nov 24 | Dec 1 |
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: Winterset 1S, Ia, about 12.2 miles away@if(!empty($station['elevation_ft'])), at 1,100 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 Truro, IA?
On average, the last spring frost (32°F) around Truro, IA is about Apr 30. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 17.
When is the first frost in the fall?
The first fall frost around Truro, IA typically arrives about Oct 3. 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 17 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 50257 Planting calendar → Iowa frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026