Frost dates for 59010Bighorn, MT
The average last spring frost in Bighorn is May 26 and the average first fall frost is September 16, giving a typical growing season of about 111 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 26
- Average first fall frost
- Sep 16
- Growing season
- 111 days
Safer after Jun 13 (1-in-10 risk)
Possible by Sep 1 (1-in-10 risk)
Last frost typically in 211 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 26 · Jun 11 · Jul 3 | Aug 21 · Sep 5 · Sep 18 | 84 days | 100% |
| Frost / freeze (32°F) | May 12 · May 26 · Jun 13 | Sep 1 · Sep 16 · Oct 1 | 111 days | 100% |
| Hard freeze (28°F) | Apr 30 · May 14 · May 28 | Sep 13 · Sep 27 · Oct 10 | 136 days | 100% |
Planting calendar for Bighorn
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 25 – Jul 1 |
| Tomatoes | Transplant outdoors | Jun 11 – May 27 |
| Peppers | Start seeds indoors | Apr 25 – May 26 |
| Peppers | Transplant outdoors | Jun 25 – Jul 26 |
| Eggplant | Start seeds indoors | May 12 – Jun 10 |
| Eggplant | Transplant outdoors | Jun 25 – Jul 26 |
| Cucumbers | Sow outdoors | Jun 25 – Jun 6 |
| Summer squash | Sow outdoors | Jun 11 – Jul 26 |
| Winter squash & pumpkins | Sow outdoors | Jun 25 – Jul 26 |
| Snap beans | Sow outdoors | Jun 11 – Jun 29 |
| Sweet corn | Sow outdoors | Jun 11 – May 27 |
| Watermelon & cantaloupe | Sow outdoors | Jun 25 – Jul 26 |
| Okra | Sow outdoors | Jun 18 – Jul 11 |
| Peas | Sow outdoors (spring) | Apr 25 – Jun 10 |
| Potatoes | Plant outdoors (spring) | Apr 25 – Jun 25 |
| Onions | Start seeds indoors (spring) | Mar 14 – Apr 10 |
| Onions | Transplant outdoors (spring) | May 12 – Jun 10 |
| Broccoli | Start seeds indoors (spring) | Apr 7 – May 11 |
| Broccoli | Transplant outdoors (spring) | May 12 – Jun 10 |
| Broccoli | Start seeds indoors (fall) | May 17 – May 27 |
| Broccoli | Transplant outdoors (fall) | Jun 16 – Jun 27 |
| Cabbage | Start seeds indoors (spring) | Mar 28 – Apr 25 |
| Cabbage | Transplant outdoors (spring) | Apr 25 – May 26 |
| Cabbage | Start seeds indoors (fall) | May 7 – Jun 6 |
| Cabbage | Transplant outdoors (fall) | Jun 6 – Jul 7 |
| Leaf lettuce | Sow outdoors (spring) | Apr 25 – Jul 11 |
| Leaf lettuce | Sow outdoors (fall) | Jun 6 – Jul 23 |
| Spinach | Sow outdoors (spring) | Apr 18 – Jun 1 |
| Spinach | Sow outdoors (fall) | Jun 23 – Jul 28 |
| Radishes | Sow outdoors (spring) | Apr 25 – Jun 15 |
| Radishes | Sow outdoors (fall) | Jun 6 – Aug 7 |
| Kale | Sow outdoors (spring) | May 12 – Jun 1 |
| Kale | Sow outdoors (fall) | May 30 – Jul 7 |
| Carrots | Sow outdoors (spring) | May 26 – Jul 11 |
| Carrots | Sow outdoors (fall) | May 7 – Jun 22 |
| Garlic | Plant outdoors (fall) | Sep 6 – Oct 7 |
Where these dates come from
ZIP code 59010 is matched to the NOAA station Hysham 25 Sse, MT, 15 km away, at 3,100 ft elevation (137 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Hysham 25 Sse, MT (used) | 3,100 ft | May 26 | Sep 16 |
| Hysham, MT | 2,669 ft | May 10 | Sep 29 |
| Hardin, MT | 2,880 ft | May 13 | Sep 29 |
| Colstrip, MT | 3,218 ft | May 15 | Sep 30 |
Frost dates near Bighorn
- Custer, MT 59024 · last May 10, first Sep 29
- Hysham, MT 59038 · last May 10, first Sep 29
- Hardin, MT 59034 · last May 13, first Sep 29
- Sanders, MT 59076 · last May 10, first Sep 29
- Crow Agency, MT 59022 · last May 13, first Sep 29
- Pompeys Pillar, MT 59064 · last May 12, first Sep 25
- Colstrip, MT 59323 · last May 15, first Sep 30
- Garryowen, MT 59031 · last May 7, first Oct 5
Frequently asked questions
- When is the last frost in Bighorn, MT?
- For ZIP code 59010, the average last spring frost (32°F) is May 26, based on NOAA 1991-2020 climate normals for the Hysham 25 Sse, MT weather station. There is a 1-in-10 chance of a frost after June 13.
- When is the first frost in Bighorn, MT?
- The average first fall frost (32°F) is September 16. There is a 1-in-10 chance of frost by September 1, so tender plants are at risk from that point on.
- How long is the growing season in 59010?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 111 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.