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Iowa frost dates
Across the 16Iowa weather stations below, the average last spring frost ranges from Apr 15 in Burlington to May 3 in Mason. The statewide middle is about Apr 26 for the last spring frost and Oct 11 for the first fall frost. Burlington has the longest growing season, about 188 days. Hardiness zones in these places: 5a, 5b, 6a.
Frost dates by city
| Place | Zone | Last spring frost | 90% safe after | First fall frost | Frost-free days |
|---|---|---|---|---|---|
| Burlington | 6a | Apr 15 | May 1 | Oct 20 | 188 |
| Lamoni | 5b | Apr 16 | May 2 | Oct 20 | 187 |
| Des Moines | 5b | Apr 18 | May 2 | Oct 20 | 185 |
| Des Moines 17 E | 5b | Apr 21 | May 5 | Oct 15 | 177 |
| Iowa | 5b | Apr 21 | May 6 | Oct 18 | 180 |
| Davenport | 5b | Apr 23 | May 8 | Oct 15 | 175 |
| Ottumwa Industrial | 5b | Apr 23 | May 7 | Oct 14 | 174 |
| Ames | 5b | Apr 26 | May 9 | Oct 8 | 165 |
| Cedar Rapids | 5a | Apr 27 | May 11 | Oct 11 | 167 |
| Waterloo | 5a | Apr 27 | May 10 | Oct 10 | 166 |
| Dubuque | 5a | Apr 28 | May 12 | Oct 11 | 166 |
| Sioux Gateway | 5a | Apr 29 | May 14 | Oct 5 | 159 |
| Marshalltown | 5a | Apr 30 | May 12 | Oct 6 | 159 |
| Estherville | 5a | May 2 | May 14 | Sep 30 | 151 |
| Spencer | 5a | May 2 | May 15 | Oct 2 | 153 |
| Mason | 5a | May 3 | May 15 | Oct 1 | 151 |
Dates are the 50% probability of a 32°F freeze (NOAA 1991–2020 normals); "90% safe after" is the date after which a later spring freeze happens in only 1 year in 10.
When to plant in Iowa
Using the statewide middle dates (last frost Apr 26, first frost Oct 11). Adjust for your town with the table above or the planting calendar.
| Plant | When to plant in Iowa |
|---|---|
| Tomatoes | May 3 – May 17 |
| Peas | Mar 15 – Apr 5; fall: Jul 19 – Aug 9 |
| Potatoes | Mar 29 – Apr 19 |
| Green beans | May 3 – May 17; fall: Jul 26 – Aug 9 |
| Garlic | Oct 11 – Nov 8 |
| Tulips | Sep 27 – Nov 8 |