Frost Dates for Casper, WY
In Casper, WY, the average last spring frost is around May 10 and the average first fall frost around Sep 29, for a growing season of about 138 days. For frost-tender plants, wait until May 24, when the chance of frost drops to 10%.
Based on NOAA 1991–2020 records from the Casper Wwtp, WY weather station, 2 miles away, elevation 5,097 ft. Frost can come earlier in low spots and valleys and later near cities and large lakes.
Frost probability by date
Chance of a 32°F frost after the spring date, or before the fall date.
| Chance | Last spring frost | First fall frost |
|---|---|---|
| 10% | May 24 | Sep 14 |
| 20% | May 19 | Sep 19 |
| 30% | May 16 | Sep 23 |
| 40% | May 13 | Sep 26 |
| 50% | May 10 | Sep 29 |
| 60% | May 8 | Oct 1 |
| 70% | May 5 | Oct 4 |
| 80% | May 3 | Oct 7 |
| 90% | Apr 30 | Oct 12 |
Light frost vs. hard freeze
Average (50%) dates for each temperature. Tender plants are damaged at 36°F; most hardy crops survive until 28°F.
| Temperature | Last in spring | First in fall |
|---|---|---|
| Light frost (36°F) | May 23 | Sep 19 |
| Frost / freeze (32°F) | May 10 | Sep 29 |
| Hard freeze (28°F) | May 1 | Oct 6 |
Planting calendar for Casper
Transplant May 17 – May 31
Transplant May 24 – Jun 7
Transplant May 24 – Jun 7
Transplant May 17 – May 31
Sow or transplant May 17 – May 31
Sow or transplant May 17 – May 31
Sow or transplant May 24 – Jun 7
Sow or transplant Apr 12 – Apr 26
Fall sowing Aug 4 – Sep 1
Fall sowing Aug 4 – Aug 25
Fall sowing Jul 21 – Aug 4
Sow or transplant Apr 12 – Apr 26
Fall sowing Jul 21 – Aug 18
Transplant Apr 26 – May 10
Fall sowing Jul 7 – Jul 21
Transplant Apr 19 – May 3
Fall sowing Jul 7 – Jul 21
Fall sowing Jul 7 – Jul 21
Fall sowing Aug 18 – Sep 8
Fall sowing Jul 21 – Aug 4
Plant Apr 12 – Apr 26
Based on the average last frost (May 10) and first frost (Sep 29). The dashed lines mark those dates. Seed packets list days to maturity; adjust for your varieties.