In Idaho, the last spring frost usually comes between April 30 and June 17, and the first fall frost between September 4 and October 11, depending on where you live. Most of Idaho is in USDA hardiness zones 5a to 7a. In the highest mountain areas, frost is possible in any month.
Find the frost dates for your ZIP code
Frost dates from NOAA 1991–2020 U.S. Climate Normals, nearest weather station. Zones derived from the 2023 USDA Plant Hardiness Zone Map data (PRISM Climate Group, Oregon State University). This is not the official USDA Plant Hardiness Zone Map.
Frost dates for Idaho cities
Dates come from the NOAA weather station closest to each city. The last spring frost and first fall frost are the typical dates, with a 30% chance of frost after (or before) them. The safer planting date has only a 10% chance of a later spring frost: use it for tender plants like tomatoes, peppers and basil.
| City | Zone | Last frost | Safer date | First frost |
|---|---|---|---|---|
| Boise | 7a | April 30 | May 9 | Oct. 14 |
| Idaho Falls | 5b | May 17 | June 2 | Sep. 25 |
| Pocatello | 6a | May 9 | May 18 | Oct. 5 |
| Coeur d’Alene | 6b | April 29 | May 6 | Oct. 12 |
| Twin Falls | 7a | May 1 | May 10 | Oct. 9 |
| Lewiston | 7a | April 14 | April 26 | Oct. 18 |
| Rexburg | 5a | May 20 | June 2 | Sep. 17 |
| Mountain Home | 7a | May 10 | May 23 | Oct. 1 |
| Burley | 6b | May 12 | May 23 | Sep. 29 |
Frost dates vary a lot across Idaho. Among the cities above, Lewiston has the earliest last frost (around April 14) and Rexburg the latest (around May 20), about 5 weeks apart. Elevation, nearby water and local terrain all make a difference, so use the dates for the place closest to you, or look up your ZIP code.
Growing zones in Idaho
Most of Idaho is in USDA hardiness zones 5a to 7a. A typical frost-free growing season lasts about 148 days, longer in the warmest areas and shorter in the coldest.
Find planting dates for the main zones in Idaho:
- Zone 5 (about 28% of ZIP codes): Tomatoes, Peppers, Potatoes, Lettuce, Green beans, Cucumbers, Garlic, Tulips
- Zone 6 (about 47% of ZIP codes): Tomatoes, Peppers, Potatoes, Lettuce, Green beans, Cucumbers, Garlic, Tulips
- Zone 7 (about 24% of ZIP codes): Tomatoes, Peppers, Potatoes, Lettuce, Green beans, Cucumbers, Garlic, Tulips
See all crops in our planting guides, or build a planting calendar for your ZIP code.
How to use frost dates
- Cool-season crops such as peas, lettuce, spinach and onions can go in several weeks before your last spring frost.
- Warm-season crops such as tomatoes, peppers, squash and beans wait until after it, when the soil has warmed.
- Fall crops are timed back from your first fall frost, and garlic and tulips are planted around it.
- Frost dates are averages. Check the forecast before setting out tender plants.
Frequently asked questions
When is the last frost in Idaho?
It depends on where you live. Across most of Idaho, the last spring frost comes between April 30 and June 17. In Boise, it is around April 30.
When is the first frost in Idaho?
Across most of Idaho, the first fall frost comes between September 4 and October 11. In Boise, it is around October 14.
What planting zone is Idaho?
Most of Idaho is in USDA hardiness zones 5a to 7a. Enter your ZIP code above to find your exact zone.
When can I plant tomatoes in Idaho?
Plant tomatoes outside after your last frost, once nights stay above 50 °F. In Boise, the safer date, with only a 10% chance of a later frost, is around May 9. See when to plant tomatoes in zone 7.
Sources. Frost dates come from the nearest NOAA weather station to each city or ZIP code. Zones come from the 2023 USDA Plant Hardiness Zone Map ZIP code data. Our zone lookup is not the official USDA map.