Frost Dates for Butte-Silver Bow, MT
In Butte-Silver Bow, MT, the average last spring frost is around Jun 13 and the average first fall frost around Sep 5, for a growing season of about 83 days. For frost-tender plants, wait until Jul 1, when the chance of frost drops to 10%.
Based on NOAA 1991–2020 records from the Butte Bert Mooney Airport, MT weather station, 9 miles away, elevation 5,506 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% | Jul 1 | Aug 24 |
| 20% | Jun 25 | Aug 28 |
| 30% | Jun 21 | Aug 31 |
| 40% | Jun 17 | Sep 3 |
| 50% | Jun 13 | Sep 5 |
| 60% | Jun 10 | Sep 8 |
| 70% | Jun 5 | Sep 11 |
| 80% | Jun 1 | Sep 14 |
| 90% | May 27 | Sep 19 |
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) | — | — |
| Frost / freeze (32°F) | Jun 13 | Sep 5 |
| Hard freeze (28°F) | May 21 | Sep 17 |
Planting calendar for Butte-Silver Bow
Transplant Jun 20 – Jul 4
Transplant Jun 27 – Jul 11
Transplant Jun 27 – Jul 11
Transplant Jun 20 – Jul 4
Sow or transplant Jun 20 – Jul 4
Sow or transplant Jun 20 – Jul 4
Sow or transplant Jun 27 – Jul 11
Sow or transplant May 16 – May 30
Fall sowing Jul 11 – Aug 8
Fall sowing Jul 11 – Aug 1
Fall sowing Jun 27 – Jul 11
Sow or transplant May 16 – May 30
Fall sowing Jun 27 – Jul 25
Transplant May 30 – Jun 13
Fall sowing Jun 13 – Jun 27
Transplant May 23 – Jun 6
Fall sowing Jun 13 – Jun 27
Fall sowing Jun 13 – Jun 27
Fall sowing Jul 25 – Aug 15
Fall sowing Jun 27 – Jul 11
Plant May 16 – May 30
Based on the average last frost (Jun 13) and first frost (Sep 5). The dashed lines mark those dates. Seed packets list days to maturity; adjust for your varieties.