Idaho Falls, ID planting zone & frost dates
Idaho Falls is in USDA hardiness zone 5b. The last spring frost usually comes around May 9 and the first fall frost around October 1, for a growing season of about 142 days.
Planting calendar for Idaho Falls
Dates are counted from the average last spring frost (May 9) using the typical timing recommended by U.S. extension services. Warm-season crops go out only after the danger of frost has passed and the soil has warmed.
| Crop | When |
|---|---|
| Tomatoes | Start seeds indoors: Mar 14 – Mar 28 Transplant outdoors: May 16 – May 23 |
| Peppers | Start seeds indoors: Feb 28 – Mar 14 Transplant outdoors: May 23 – May 30 |
| Eggplant | Start seeds indoors: Feb 28 – Mar 14 Transplant outdoors: May 23 – May 30 |
| Broccoli | Start seeds indoors: Feb 28 – Mar 14 Transplant outdoors: Apr 11 – Apr 25 |
| Cabbage | Start seeds indoors: Feb 28 – Mar 14 Transplant outdoors: Apr 11 – Apr 25 |
| Onions (sets) | Plant outdoors: Apr 11 – Apr 25 |
| Peas | Sow outdoors: Mar 28 – Apr 11 |
| Spinach | Sow outdoors: Mar 28 – Apr 11 |
| Lettuce | Sow outdoors: Apr 11 – Apr 25 |
| Carrots | Sow outdoors: Apr 11 – Apr 25 |
| Potatoes | Plant outdoors: Apr 11 – Apr 25 |
| Beans | Sow outdoors: May 16 – May 23 |
| Sweet corn | Sow outdoors: May 16 – May 23 |
| Cucumbers | Sow outdoors: May 16 – May 23 |
| Squash & zucchini | Sow outdoors: May 16 – May 23 |
| Basil | Start seeds indoors: Mar 28 – Apr 11 Transplant outdoors: May 16 – May 23 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Aug 6 (8 weeks before the average first fall frost on Oct 1).
Useful for zone 5b gardens
- Seed starting kit with dome — to start seeds indoors before the last frost
- LED grow light for seedlings — stops leggy seedlings
- Frost cloth / plant covers — for late spring and early fall frosts
- Soil thermometer — warm-season crops need soil above 60°F
- Cold frame / mini greenhouse — adds weeks to a short season
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Frost risk in detail
| 90% chance | 50% chance | 10% chance | |
|---|---|---|---|
| Last 32°F frost in spring is after | Apr 27 | May 9 | Jun 2 |
| First 32°F frost in fall is before | Oct 15 | Oct 1 | Sep 17 |
How to read it: in spring there is a 10% chance of a frost after June 2, so that is a safe date for tender plants. In fall there is a 10% chance of frost before September 17. A hard freeze (28°F) usually ends around April 28.
Hardiness zone by ZIP code in Idaho Falls
- 83401 zone 5b
- 83402 zone 5b
- 83403 zone 5b
- 83404 zone 5b
- 83405 zone 5b
- 83406 zone 5b
- 83415 zone 5b
Nearby cities
Questions
What growing zone is Idaho Falls, ID?
Idaho Falls is in USDA Plant Hardiness Zone 5b (average extreme winter low -15°F to -10°F), according to the USDA 2023 map.
When is the last frost in Idaho Falls?
The average last spring frost (32°F) in Idaho Falls is May 9. There is still a 10% chance of frost until June 2.
When can I plant tomatoes in Idaho Falls?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around May 16 – May 23. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Idaho Falls - Kifi, ID (USC00104455), 5.5 km (3.4 mi) from the city center, elevation 1445 m, based on 24 years of records. Hardiness zone: USDA Plant Hardiness Zone Map 2023 for the ZIP code nearest to the city center. Microclimates (valleys, hills, cities, coasts) can be warmer or colder: check the local forecast before planting. How we calculate the data.