Frost dates for 83229Cobalt, ID
The average last spring frost in Cobalt is May 14 and the average first fall frost is September 25, giving a typical growing season of about 131 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 14
- Average first fall frost
- Sep 25
- Growing season
- 131 days
Safer after Jun 2 (1-in-10 risk)
Possible by Sep 10 (1-in-10 risk)
Last frost typically in 197 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 17 · Jun 4 · Jun 21 | Aug 31 · Sep 14 · Sep 26 | 100 days | 100% |
| Frost / freeze (32°F) | May 2 · May 14 · Jun 2 | Sep 10 · Sep 25 · Oct 7 | 131 days | 100% |
| Hard freeze (28°F) | Apr 19 · May 1 · May 12 | Sep 24 · Oct 7 · Oct 21 | 158 days | 100% |
Planting calendar for Cobalt
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 13 – Jun 19 |
| Tomatoes | Transplant outdoors | May 30 – Jun 5 |
| Peppers | Start seeds indoors | Apr 13 – May 14 |
| Peppers | Transplant outdoors | Jun 13 – Jul 14 |
| Eggplant | Start seeds indoors | Apr 30 – May 29 |
| Eggplant | Transplant outdoors | Jun 13 – Jul 14 |
| Cucumbers | Sow outdoors | Jun 13 – Jun 15 |
| Summer squash | Sow outdoors | May 30 – Jul 14 |
| Winter squash & pumpkins | Sow outdoors | Jun 13 – Jul 14 |
| Snap beans | Sow outdoors | May 30 – Jul 8 |
| Sweet corn | Sow outdoors | May 30 – Jun 5 |
| Watermelon & cantaloupe | Sow outdoors | Jun 13 – Jul 14 |
| Okra | Sow outdoors | Jun 6 – Jun 29 |
| Peas | Sow outdoors (spring) | Apr 13 – May 29 |
| Potatoes | Plant outdoors (spring) | Apr 13 – Jun 13 |
| Onions | Start seeds indoors (spring) | Mar 2 – Mar 29 |
| Onions | Transplant outdoors (spring) | Apr 30 – May 29 |
| Broccoli | Start seeds indoors (spring) | Mar 26 – Apr 29 |
| Broccoli | Transplant outdoors (spring) | Apr 30 – May 29 |
| Broccoli | Start seeds indoors (fall) | May 26 – Jun 5 |
| Broccoli | Transplant outdoors (fall) | Jun 25 – Jul 6 |
| Cabbage | Start seeds indoors (spring) | Mar 16 – Apr 13 |
| Cabbage | Transplant outdoors (spring) | Apr 13 – May 14 |
| Cabbage | Start seeds indoors (fall) | May 16 – Jun 15 |
| Cabbage | Transplant outdoors (fall) | Jun 15 – Jul 16 |
| Leaf lettuce | Sow outdoors (spring) | Apr 13 – Jun 29 |
| Leaf lettuce | Sow outdoors (fall) | Jun 15 – Aug 1 |
| Spinach | Sow outdoors (spring) | Apr 6 – May 20 |
| Spinach | Sow outdoors (fall) | Jul 2 – Aug 6 |
| Radishes | Sow outdoors (spring) | Apr 13 – Jun 3 |
| Radishes | Sow outdoors (fall) | Jun 15 – Aug 16 |
| Kale | Sow outdoors (spring) | Apr 30 – May 20 |
| Kale | Sow outdoors (fall) | Jun 8 – Jul 16 |
| Carrots | Sow outdoors (spring) | May 14 – Jun 29 |
| Carrots | Sow outdoors (fall) | May 16 – Jul 1 |
| Garlic | Plant outdoors (fall) | Sep 15 – Oct 16 |
Where these dates come from
ZIP code 83229 is matched to the NOAA station Challis Ap, ID, 63.4 km away, at 5,033 ft elevation (23 ft lower than the ZIP code's center). This station is relatively far away, so local dates may differ more than usual. Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Challis Ap, ID (used) | 5,033 ft | May 14 | Sep 25 |
| Salmon-Ksra, ID | 3,953 ft | May 17 | Sep 24 |
| Shoup, ID | 3,400 ft | May 3 | Oct 8 |
| Taylor Rch, ID | 3,835 ft | May 11 | Sep 30 |
Frost dates near Cobalt
- Salmon, ID 83467 · last May 17, first Sep 24
- Shoup, ID 83469 · last May 3, first Oct 8
- Carmen, ID 83462 · last May 17, first Sep 24
- Tendoy, ID 83468 · last —, first —
- North Fork, ID 83466 · last —, first —
- Ellis, ID 83235 · last Jun 12, first Sep 6
- Lemhi, ID 83465 · last Jun 12, first Sep 6
- Gibbonsville, ID 83463 · last —, first —
Frequently asked questions
- When is the last frost in Cobalt, ID?
- For ZIP code 83229, the average last spring frost (32°F) is May 14, based on NOAA 1991-2020 climate normals for the Challis Ap, ID weather station. There is a 1-in-10 chance of a frost after June 2.
- When is the first frost in Cobalt, ID?
- The average first fall frost (32°F) is September 25. There is a 1-in-10 chance of frost by September 10, so tender plants are at risk from that point on.
- How long is the growing season in 83229?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 131 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.