Last spring frost
Apr 29
Frost Dates for Hills, IA
First fall frost
Oct 9
Growing season
162 days
Hardiness zone
5b
In an average year around Hills, IA, the last spring frost (32°F) is about Apr 29 and the first fall frost is about Oct 9, giving roughly a 162-day growing season. To be safe most years, wait until Apr 14 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 21 | May 7 | Apr 24 |
| Freeze (32°F) | May 14 | Apr 29 | Apr 14 |
| Hard (28°F) | May 5 | Apr 18 | Apr 3 |
| Severe (24°F) | Apr 25 | Apr 6 | Mar 22 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 21 | May 16 | May 14 | May 10 | May 7 | May 5 | May 1 | Apr 29 | Apr 24 |
| 32°F | May 14 | May 8 | May 5 | May 1 | Apr 29 | Apr 26 | Apr 23 | Apr 18 | Apr 14 |
| 28°F | May 5 | Apr 30 | Apr 25 | Apr 22 | Apr 18 | Apr 16 | Apr 12 | Apr 8 | Apr 3 |
| 24°F | Apr 25 | Apr 19 | Apr 13 | Apr 9 | Apr 6 | Apr 4 | Apr 1 | Mar 29 | Mar 22 |
| 20°F | Apr 14 | Apr 6 | Apr 3 | Apr 1 | Mar 29 | Mar 26 | Mar 21 | Mar 17 | Mar 11 |
| 16°F | Apr 2 | Mar 29 | Mar 25 | Mar 21 | Mar 17 | Mar 13 | Mar 10 | Mar 7 | Mar 1 |
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 17 | Oct 1 | Oct 12 |
| Freeze (32°F) | Sep 25 | Oct 9 | Oct 22 |
| Hard (28°F) | Oct 3 | Oct 20 | Nov 1 |
| Severe (24°F) | Oct 17 | Oct 30 | Nov 11 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 17 | Sep 22 | Sep 26 | Sep 28 | Oct 1 | Oct 3 | Oct 5 | Oct 8 | Oct 12 |
| 32°F | Sep 25 | Sep 30 | Oct 3 | Oct 6 | Oct 9 | Oct 12 | Oct 15 | Oct 18 | Oct 22 |
| 28°F | Oct 3 | Oct 10 | Oct 14 | Oct 18 | Oct 20 | Oct 22 | Oct 24 | Oct 27 | Nov 1 |
| 24°F | Oct 17 | Oct 21 | Oct 25 | Oct 28 | Oct 30 | Nov 1 | Nov 3 | Nov 7 | Nov 11 |
| 20°F | Oct 28 | Nov 1 | Nov 3 | Nov 6 | Nov 8 | Nov 11 | Nov 14 | Nov 17 | Nov 23 |
| 16°F | Nov 5 | Nov 8 | Nov 12 | Nov 15 | Nov 18 | Nov 21 | Nov 24 | Nov 28 | Dec 3 |
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: Iowa City, Ia, about 2.6 miles away@if(!empty($station['elevation_ft'])), at 640 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 Hills, IA?
On average, the last spring frost (32°F) around Hills, IA is about Apr 29. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 14.
When is the first frost in the fall?
The first fall frost around Hills, IA typically arrives about Oct 9. 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 29 on average, or Apr 14 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 162 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 52235 Planting calendar → Iowa frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026