Frost dates for 83420Ashton, ID
The average last spring frost in Ashton is May 21 and the average first fall frost is September 21, giving a typical growing season of about 121 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 21
- Average first fall frost
- Sep 21
- Growing season
- 121 days
Safer after Jun 13 (1-in-10 risk)
Possible by Sep 4 (1-in-10 risk)
Last frost typically in 199 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 22 · Jun 10 · Jul 2 | Aug 22 · Sep 7 · Sep 24 | 88 days | 100% |
| Frost / freeze (32°F) | May 4 · May 21 · Jun 13 | Sep 4 · Sep 21 · Oct 7 | 121 days | 100% |
| Hard freeze (28°F) | Apr 16 · May 3 · May 26 | Sep 13 · Oct 4 · Oct 20 | 152 days | 100% |
Planting calendar for Ashton
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 20 – Jun 26 |
| Tomatoes | Transplant outdoors | Jun 6 – Jun 1 |
| Peppers | Start seeds indoors | Apr 20 – May 21 |
| Peppers | Transplant outdoors | Jun 20 – Jul 21 |
| Eggplant | Start seeds indoors | May 7 – Jun 5 |
| Eggplant | Transplant outdoors | Jun 20 – Jul 21 |
| Cucumbers | Sow outdoors | Jun 20 – Jun 11 |
| Summer squash | Sow outdoors | Jun 6 – Jul 21 |
| Winter squash & pumpkins | Sow outdoors | Jun 20 – Jul 21 |
| Snap beans | Sow outdoors | Jun 6 – Jul 4 |
| Sweet corn | Sow outdoors | Jun 6 – Jun 1 |
| Watermelon & cantaloupe | Sow outdoors | Jun 20 – Jul 21 |
| Okra | Sow outdoors | Jun 13 – Jul 6 |
| Peas | Sow outdoors (spring) | Apr 20 – Jun 5 |
| Potatoes | Plant outdoors (spring) | Apr 20 – Jun 20 |
| Onions | Start seeds indoors (spring) | Mar 9 – Apr 5 |
| Onions | Transplant outdoors (spring) | May 7 – Jun 5 |
| Broccoli | Start seeds indoors (spring) | Apr 2 – May 6 |
| Broccoli | Transplant outdoors (spring) | May 7 – Jun 5 |
| Broccoli | Start seeds indoors (fall) | May 22 – Jun 1 |
| Broccoli | Transplant outdoors (fall) | Jun 21 – Jul 2 |
| Cabbage | Start seeds indoors (spring) | Mar 23 – Apr 20 |
| Cabbage | Transplant outdoors (spring) | Apr 20 – May 21 |
| Cabbage | Start seeds indoors (fall) | May 12 – Jun 11 |
| Cabbage | Transplant outdoors (fall) | Jun 11 – Jul 12 |
| Leaf lettuce | Sow outdoors (spring) | Apr 20 – Jul 6 |
| Leaf lettuce | Sow outdoors (fall) | Jun 11 – Jul 28 |
| Spinach | Sow outdoors (spring) | Apr 13 – May 27 |
| Spinach | Sow outdoors (fall) | Jun 28 – Aug 2 |
| Radishes | Sow outdoors (spring) | Apr 20 – Jun 10 |
| Radishes | Sow outdoors (fall) | Jun 11 – Aug 12 |
| Kale | Sow outdoors (spring) | May 7 – May 27 |
| Kale | Sow outdoors (fall) | Jun 4 – Jul 12 |
| Carrots | Sow outdoors (spring) | May 21 – Jul 6 |
| Carrots | Sow outdoors (fall) | May 12 – Jun 27 |
| Garlic | Plant outdoors (fall) | Sep 11 – Oct 12 |
Where these dates come from
ZIP code 83420 is matched to the NOAA station Ashton 1N, ID, 6.7 km away, at 5,212 ft elevation (136 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Ashton 1N, ID (used) | 5,212 ft | May 21 | Sep 21 |
| Tetonia Exp Stn, ID | 6,170 ft | Jun 15 | Sep 7 |
| Saint Anthony, ID | 4,910 ft | May 17 | Sep 22 |
| Sugar City, ID | 4,925 ft | May 29 | Sep 13 |
Frost dates near Ashton
- Chester, ID 83421 · last May 21, first Sep 21
- Newdale, ID 83436 · last May 17, first Sep 22
- Teton, ID 83451 · last May 17, first Sep 22
- Saint Anthony, ID 83445 · last May 17, first Sep 22
- Felt, ID 83424 · last Jun 15, first Sep 7
- Parker, ID 83438 · last May 17, first Sep 22
- Sugar City, ID 83448 · last May 15, first Sep 23
- Tetonia, ID 83452 · last Jun 13, first Sep 9
Frequently asked questions
- When is the last frost in Ashton, ID?
- For ZIP code 83420, the average last spring frost (32°F) is May 21, based on NOAA 1991-2020 climate normals for the Ashton 1N, ID weather station. There is a 1-in-10 chance of a frost after June 13.
- When is the first frost in Ashton, ID?
- The average first fall frost (32°F) is September 21. There is a 1-in-10 chance of frost by September 4, so tender plants are at risk from that point on.
- How long is the growing season in 83420?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 121 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.