Frost dates / By state
Frost dates in Idaho
NOAA 1991–2020 normals for a 32 °F freeze. Your own yard can run a little either side.
Short answer
Across 16 NOAA weather stations in Idaho, the average last spring frost runs from April 6 at Lewiston Nez Perce Co Airport to June 11 at Idaho Falls 46 W. The first fall frost comes as early as September 6 at Idaho Falls 46 W and as late as October 26 at Lewiston Nez Perce Co Airport. At 1 of the 17 stations, a freeze can come in any month. Planting zones near these stations run from 5a to 7b.
Idaho cities
- Frost dates in Boise City: last frost April 24, first frost October 21
- Frost dates in Meridian: last frost April 24, first frost October 21
Find yours by ZIP code
The table below is by weather station. For the station nearest you, and your planting zone, type your ZIP code.
Idaho frost dates by weather station
| Station | Last spring frost | First fall frost | Frost-free | Zone nearby |
|---|---|---|---|---|
| Arco 17 SW 5,920 ft | May 24 1 in 10 after June 15 | October 1 1 in 10 by September 16 | 130 days | 5a |
| Boise Air Terminal 2,814 ft | April 24 1 in 10 after May 9 | October 21 1 in 10 by October 5 | 180 days | 7a |
| Burley Muni Airport 4,142 ft | May 7 1 in 10 after May 23 | October 4 1 in 10 by September 21 | 150 days | 6b |
| Challis Airport 5,033 ft | May 14 1 in 10 after June 2 | September 25 1 in 10 by September 10 | 134 days | – |
| Idaho Falls 46 W 4,938 ft | June 11 1 in 10 after July 1 | September 6 1 in 10 by August 24 | 87 days | – |
| Idaho Falls Fanning Fld 4,729 ft | May 23 1 in 10 after June 13 | September 20 1 in 10 by September 1 | 120 days | 5b |
| Jerome Co Airport 4,048 ft | May 1 1 in 10 after May 16 | October 14 1 in 10 by September 29 | 166 days | 6b |
| Lewiston Nez Perce Co Airport 1,436 ft | April 6 1 in 10 after April 26 | October 26 1 in 10 by October 10 | 203 days | 7b |
| Lowell Three Rivers 1,480 ft | April 16 1 in 10 after May 4 | October 25 1 in 10 by October 5 | 192 days | – |
| Malad City 4,470 ft | May 22 1 in 10 after June 16 | September 20 1 in 10 by September 4 | 121 days | 6a |
| Mccall Airport 5,013 ft | June 10 1 in 10 after June 28 | September 10 1 in 10 by August 29 | 92 days | – |
| Mullan Pass Vor/Dme 6,028 ft | June 10 1 in 10 after June 25 | September 23 1 in 10 by September 4 | 105 days | 6a |
| Murphy 10 W 3,950 ft | May 17 1 in 10 after June 6 | September 30 1 in 10 by September 14 | 136 days | – |
| Pocatello Rgnl Airport 4,478 ft | May 23 1 in 10 after June 13 | September 18 1 in 10 by September 3 | 118 days | 6a |
| Rexburg Madison Co Airport 4,858 ft | May 15 1 in 10 after June 3 | September 23 1 in 10 by September 8 | 131 days | 5a |
| Stanley Rs 6,495 ft | A freeze is possible in any month | – | ||
| Twin Falls Sun Vly Rgnl Airport 4,151 ft | May 9 1 in 10 after May 28 | October 4 1 in 10 by September 20 | 148 days | 6b |
The average date is NOAA's 50% date: half of years have a later last frost, or an earlier first one. Plan by the 1-in-10 date if a freeze would cost you plants. Stations are NOAA's main weather stations, mostly airports. “Zone nearby” is the USDA 2023 zone of the nearest ZIP code within 10 miles. NOAA counts the frost season from August to July, so in the warmest places the “first fall” freeze lands after New Year.
How these dates work
Frost dates come from NOAA's 1991 to 2020 Climate Normals, which work out from each weather station's daily lows how likely the last spring freeze and the first fall freeze (32 °F) are by each date. We use the station nearest the middle of your ZIP code and show its height and distance, since a station on a hill or by a lake can differ from your yard.
The average date is the 50% date: half of years have a freeze after the spring date or before the fall one. The 1-in-10 dates are NOAA's 10% dates, the ones to plan by if a late freeze would cost you plants. Within one yard, cold air pools in low spots while walls and paving hold heat, so some corners freeze before others.
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Where the numbers come from
- USDA Plant Hardiness Zone Map, 2023. Agricultural Research Service, U.S. Department of Agriculture
- PRISM Climate Group, Oregon State University (zone data)
- NOAA NCEI, U.S. Climate Normals 1991–2020, annual/seasonal
- NOAA, Normals calculation methodology (frost-freeze probability dates)
- US Census Bureau, 2025 ZCTA gazetteer (ZIP code centers)