Frost Dates for Missoula, MT
In Missoula, MT, the average last spring frost is around May 10 and the average first fall frost around Oct 1, for a growing season of about 143 days. For frost-tender plants, wait until May 28, when the chance of frost drops to 10%.
Based on NOAA 1991–2020 records from the Missoula 2 Ne, MT weather station, 3 miles away, elevation 3,420 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 28 | Sep 16 |
| 20% | May 22 | Sep 22 |
| 30% | May 17 | Sep 26 |
| 40% | May 14 | Sep 28 |
| 50% | May 10 | Oct 1 |
| 60% | May 7 | Oct 3 |
| 70% | May 5 | Oct 6 |
| 80% | May 2 | Oct 10 |
| 90% | Apr 27 | Oct 15 |
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) | Jun 1 | Sep 19 |
| Frost / freeze (32°F) | May 10 | Oct 1 |
| Hard freeze (28°F) | Apr 28 | Oct 12 |
Planting calendar for Missoula
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 6 – Sep 3
Fall sowing Aug 6 – Aug 27
Fall sowing Jul 23 – Aug 6
Sow or transplant Apr 12 – Apr 26
Fall sowing Jul 23 – Aug 20
Transplant Apr 26 – May 10
Fall sowing Jul 9 – Jul 23
Transplant Apr 19 – May 3
Fall sowing Jul 9 – Jul 23
Fall sowing Jul 9 – Jul 23
Fall sowing Aug 20 – Sep 10
Fall sowing Jul 23 – Aug 6
Plant Apr 12 – Apr 26
Based on the average last frost (May 10) and first frost (Oct 1). The dashed lines mark those dates. Seed packets list days to maturity; adjust for your varieties.