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Idaho frost dates
Across the 16Idaho weather stations below, the average last spring frost ranges from Apr 6 in Lewiston Nez Perce to Jun 11 in Idaho Falls 46 W. The statewide middle is about May 16 for the last spring frost and Sep 27 for the first fall frost. Lewiston Nez Perce has the longest growing season, about 203 days. Hardiness zones in these places: 4b, 5a, 5b, 6a, 6b, 7a, 7b.
Frost dates by city
| Place | Zone | Last spring frost | 90% safe after | First fall frost | Frost-free days |
|---|---|---|---|---|---|
| Lewiston Nez Perce | 7b | Apr 6 | Apr 26 | Oct 26 | 203 |
| Lowell Three Rivers | 7a | Apr 16 | May 4 | Oct 25 | 192 |
| Boise Air Terminal | 7a | Apr 24 | May 9 | Oct 21 | 180 |
| Jerome | 6b | May 1 | May 16 | Oct 14 | 166 |
| Burley | 6b | May 7 | May 23 | Oct 4 | 150 |
| Twin Falls Sun Vly | 6b | May 9 | May 28 | Oct 4 | 148 |
| Challis | 5b | May 14 | Jun 2 | Sep 25 | 134 |
| Rexburg Madison | 5a | May 15 | Jun 3 | Sep 23 | 131 |
| Murphy 10 W | 7a | May 17 | Jun 6 | Sep 30 | 136 |
| Malad | 6a | May 22 | Jun 16 | Sep 20 | 121 |
| Idaho Falls Fanning | 5b | May 23 | Jun 13 | Sep 20 | 120 |
| Pocatello | 6a | May 23 | Jun 13 | Sep 18 | 118 |
| Arco 17 Sw | 5a | May 24 | Jun 15 | Oct 1 | 130 |
| Mccall | 5a | Jun 10 | Jun 28 | Sep 10 | 92 |
| Mullan Pass Vor/Dme | 6a | Jun 10 | Jun 25 | Sep 23 | 105 |
| Idaho Falls 46 W | 4b | Jun 11 | Jul 1 | Sep 6 | 87 |
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 Idaho
Using the statewide middle dates (last frost May 16, first frost Sep 27). Adjust for your town with the table above or the planting calendar.
| Plant | When to plant in Idaho |
|---|---|
| Tomatoes | May 23 – Jun 6 |
| Peas | Apr 4 – Apr 25; fall: Jul 5 – Jul 26 |
| Potatoes | Apr 18 – May 9 |
| Green beans | May 23 – Jun 6; fall: Jul 12 – Jul 26 |
| Garlic | Sep 27 – Oct 25 |
| Tulips | Sep 13 – Oct 25 |