Frost dates for 82601Casper, WY
The average last spring frost in Casper is May 10 and the average first fall frost is September 29, giving a typical growing season of about 138 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 10
- Average first fall frost
- Sep 29
- Growing season
- 138 days
Safer after May 24 (1-in-10 risk)
Possible by Sep 14 (1-in-10 risk)
Last frost typically in 195 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 11 · May 23 · Jun 6 | Sep 6 · Sep 19 · Oct 2 | 116 days | 100% |
| Frost / freeze (32°F) | Apr 30 · May 10 · May 24 | Sep 14 · Sep 29 · Oct 12 | 138 days | 100% |
| Hard freeze (28°F) | Apr 17 · May 1 · May 14 | Sep 21 · Oct 6 · Oct 23 | 156 days | 100% |
Planting calendar for Casper
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 9 – Jun 15 |
| Tomatoes | Transplant outdoors | May 26 – Jun 9 |
| Peppers | Start seeds indoors | Apr 9 – May 10 |
| Peppers | Transplant outdoors | Jun 9 – Jul 10 |
| Eggplant | Start seeds indoors | Apr 26 – May 25 |
| Eggplant | Transplant outdoors | Jun 9 – Jul 10 |
| Cucumbers | Sow outdoors | Jun 9 – Jun 19 |
| Summer squash | Sow outdoors | May 26 – Jul 10 |
| Winter squash & pumpkins | Sow outdoors | Jun 9 – Jul 10 |
| Snap beans | Sow outdoors | May 26 – Jul 12 |
| Sweet corn | Sow outdoors | May 26 – Jun 9 |
| Watermelon & cantaloupe | Sow outdoors | Jun 9 – Jul 10 |
| Okra | Sow outdoors | Jun 2 – Jun 25 |
| Peas | Sow outdoors (spring) | Apr 9 – May 25 |
| Potatoes | Plant outdoors (spring) | Apr 9 – Jun 9 |
| Onions | Start seeds indoors (spring) | Feb 26 – Mar 25 |
| Onions | Transplant outdoors (spring) | Apr 26 – May 25 |
| Broccoli | Start seeds indoors (spring) | Mar 22 – Apr 25 |
| Broccoli | Transplant outdoors (spring) | Apr 26 – May 25 |
| Broccoli | Start seeds indoors (fall) | May 30 – Jun 9 |
| Broccoli | Transplant outdoors (fall) | Jun 29 – Jul 10 |
| Cabbage | Start seeds indoors (spring) | Mar 12 – Apr 9 |
| Cabbage | Transplant outdoors (spring) | Apr 9 – May 10 |
| Cabbage | Start seeds indoors (fall) | May 20 – Jun 19 |
| Cabbage | Transplant outdoors (fall) | Jun 19 – Jul 20 |
| Leaf lettuce | Sow outdoors (spring) | Apr 9 – Jun 25 |
| Leaf lettuce | Sow outdoors (fall) | Jun 19 – Aug 5 |
| Spinach | Sow outdoors (spring) | Apr 2 – May 16 |
| Spinach | Sow outdoors (fall) | Jul 6 – Aug 10 |
| Radishes | Sow outdoors (spring) | Apr 9 – May 30 |
| Radishes | Sow outdoors (fall) | Jun 19 – Aug 20 |
| Kale | Sow outdoors (spring) | Apr 26 – May 16 |
| Kale | Sow outdoors (fall) | Jun 12 – Jul 20 |
| Carrots | Sow outdoors (spring) | May 10 – Jun 25 |
| Carrots | Sow outdoors (fall) | May 20 – Jul 5 |
| Garlic | Plant outdoors (fall) | Sep 19 – Oct 20 |
Where these dates come from
ZIP code 82601 is matched to the NOAA station Casper Wwtp, WY, 2.6 km away, at 5,097 ft elevation (47 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Casper Wwtp, WY (used) | 5,097 ft | May 10 | Sep 29 |
| Casper 1Sw, WY | 5,143 ft | May 12 | Oct 1 |
| Casper Natrona Co Ap, WY | 5,338 ft | May 26 | Sep 22 |
| Bates Creek #2, WY | 6,042 ft | May 22 | Sep 26 |
Frost dates near Casper
- Casper, WY 82605 · last May 10, first Sep 29
- Mills, WY 82644 · last May 10, first Sep 29
- Evansville, WY 82636 · last May 10, first Sep 29
- Glenrock, WY 82637 · last May 10, first Sep 29
- Natrona, WY 82646 · last May 23, first Sep 20
- Alcova, WY 82620 · last May 9, first Oct 7
- Powder River, WY 82648 · last May 30, first Sep 22
- Edgerton, WY 82635 · last May 22, first Sep 22
Frequently asked questions
- When is the last frost in Casper, WY?
- For ZIP code 82601, the average last spring frost (32°F) is May 10, based on NOAA 1991-2020 climate normals for the Casper Wwtp, WY weather station. There is a 1-in-10 chance of a frost after May 24.
- When is the first frost in Casper, WY?
- The average first fall frost (32°F) is September 29. There is a 1-in-10 chance of frost by September 14, so tender plants are at risk from that point on.
- How long is the growing season in 82601?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 138 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.