Frost dates for 83402Idaho Falls, ID
The average last spring frost in Idaho Falls is May 23 and the average first fall frost is September 20, giving a typical growing season of about 114 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 23
- Average first fall frost
- Sep 20
- Growing season
- 114 days
Safer after Jun 13 (1-in-10 risk)
Possible by Sep 1 (1-in-10 risk)
Last frost typically in 201 days
Frost risk by date
NOAA reports frost dates as probabilities. The middle date is the average (a 50% chance). For spring, the 10% date is a safer planting date: frost after it happens in about 1 year in 10. Light frost (36°F) can damage tender plants; a hard freeze (28°F) kills most annuals.
| Temperature | Last spring: 90% / 50% / 10% chance | First fall: 10% / 50% / 90% chance | Growing season (50%) | Years with at least one |
|---|---|---|---|---|
| Light frost (36°F) | May 28 · Jun 14 · Jul 2 | Aug 20 · Sep 5 · Sep 22 | 79 days | 100% |
| Frost / freeze (32°F) | May 7 · May 23 · Jun 13 | Sep 1 · Sep 20 · Oct 4 | 114 days | 100% |
| Hard freeze (28°F) | Apr 23 · May 7 · May 23 | Sep 15 · Oct 2 · Oct 16 | 146 days | 100% |
Planting calendar for Idaho Falls
Planting windows from the University of Maryland Extension calendar, shifted to your average frost dates. Use them as a starting point and adjust for seed packet instructions and local conditions.
| Crop | Task | Window |
|---|---|---|
| Tomatoes | Start seeds indoors | Apr 22 – Jun 28 |
| Tomatoes | Transplant outdoors | Jun 8 – May 31 |
| Peppers | Start seeds indoors | Apr 22 – May 23 |
| Peppers | Transplant outdoors | Jun 22 – Jul 23 |
| Eggplant | Start seeds indoors | May 9 – Jun 7 |
| Eggplant | Transplant outdoors | Jun 22 – Jul 23 |
| Cucumbers | Sow outdoors | Jun 22 – Jun 10 |
| Summer squash | Sow outdoors | Jun 8 – Jul 23 |
| Winter squash & pumpkins | Sow outdoors | Jun 22 – Jul 23 |
| Snap beans | Sow outdoors | Jun 8 – Jul 3 |
| Sweet corn | Sow outdoors | Jun 8 – May 31 |
| Watermelon & cantaloupe | Sow outdoors | Jun 22 – Jul 23 |
| Okra | Sow outdoors | Jun 15 – Jul 8 |
| Peas | Sow outdoors (spring) | Apr 22 – Jun 7 |
| Potatoes | Plant outdoors (spring) | Apr 22 – Jun 22 |
| Onions | Start seeds indoors (spring) | Mar 11 – Apr 7 |
| Onions | Transplant outdoors (spring) | May 9 – Jun 7 |
| Broccoli | Start seeds indoors (spring) | Apr 4 – May 8 |
| Broccoli | Transplant outdoors (spring) | May 9 – Jun 7 |
| Broccoli | Start seeds indoors (fall) | May 21 – May 31 |
| Broccoli | Transplant outdoors (fall) | Jun 20 – Jul 1 |
| Cabbage | Start seeds indoors (spring) | Mar 25 – Apr 22 |
| Cabbage | Transplant outdoors (spring) | Apr 22 – May 23 |
| Cabbage | Start seeds indoors (fall) | May 11 – Jun 10 |
| Cabbage | Transplant outdoors (fall) | Jun 10 – Jul 11 |
| Leaf lettuce | Sow outdoors (spring) | Apr 22 – Jul 8 |
| Leaf lettuce | Sow outdoors (fall) | Jun 10 – Jul 27 |
| Spinach | Sow outdoors (spring) | Apr 15 – May 29 |
| Spinach | Sow outdoors (fall) | Jun 27 – Aug 1 |
| Radishes | Sow outdoors (spring) | Apr 22 – Jun 12 |
| Radishes | Sow outdoors (fall) | Jun 10 – Aug 11 |
| Kale | Sow outdoors (spring) | May 9 – May 29 |
| Kale | Sow outdoors (fall) | Jun 3 – Jul 11 |
| Carrots | Sow outdoors (spring) | May 23 – Jul 8 |
| Carrots | Sow outdoors (fall) | May 11 – Jun 26 |
| Garlic | Plant outdoors (fall) | Sep 10 – Oct 11 |
Where these dates come from
ZIP code 83402 is matched to the NOAA station Idaho Falls Fanning Fld, ID, 2.7 km away, at 4,729 ft elevation (18 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Idaho Falls Fanning Fld, ID (used) | 4,729 ft | May 23 | Sep 20 |
| Idaho Falls - Kifi, ID | 4,742 ft | May 9 | Oct 1 |
| Rigby, ID | 4,856 ft | May 9 | Oct 5 |
| Idaho Falls 16 Se, ID | 5,828 ft | Jun 9 | Sep 11 |
Frost dates near Idaho Falls
- Idaho Falls, ID 83403 · last May 9, first Oct 1
- Iona, ID 83427 · last May 9, first Oct 1
- Shelley, ID 83274 · last May 23, first Sep 20
- Ucon, ID 83454 · last May 9, first Oct 1
- Lewisville, ID 83431 · last May 9, first Oct 1
- Basalt, ID 83218 · last May 5, first Oct 3
- Firth, ID 83236 · last May 5, first Oct 3
- Rigby, ID 83442 · last May 9, first Oct 5
Frequently asked questions
- When is the last frost in Idaho Falls, ID?
- For ZIP code 83402, the average last spring frost (32°F) is May 23, based on NOAA 1991-2020 climate normals for the Idaho Falls Fanning Fld, ID weather station. There is a 1-in-10 chance of a frost after June 13.
- When is the first frost in Idaho Falls, ID?
- The average first fall frost (32°F) is September 20. There is a 1-in-10 chance of frost by September 1, so tender plants are at risk from that point on.
- How long is the growing season in 83402?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 114 days long.
- Are these frost dates a forecast?
- No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.