Frost dates for 59910Big Arm, MT
The average last spring frost in Big Arm is May 10 and the average first fall frost is October 5, giving a typical growing season of about 147 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 10
- Average first fall frost
- Oct 5
- Growing season
- 147 days
Safer after May 26 (1-in-10 risk)
Possible by Sep 22 (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 28 · Jun 16 | Sep 9 · Sep 26 · Oct 7 | 118 days | 100% |
| Frost / freeze (32°F) | Apr 27 · May 10 · May 26 | Sep 22 · Oct 5 · Oct 19 | 147 days | 100% |
| Hard freeze (28°F) | Apr 7 · Apr 28 · May 13 | Oct 1 · Oct 16 · Nov 1 | 171 days | 100% |
Planting calendar for Big Arm
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 15 |
| 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 25 |
| Summer squash | Sow outdoors | May 26 – Jul 10 |
| Winter squash & pumpkins | Sow outdoors | Jun 9 – Jul 10 |
| Snap beans | Sow outdoors | May 26 – Jul 18 |
| Sweet corn | Sow outdoors | May 26 – Jun 15 |
| 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) | Jun 5 – Jun 15 |
| Broccoli | Transplant outdoors (fall) | Jul 5 – Jul 16 |
| Cabbage | Start seeds indoors (spring) | Mar 12 – Apr 9 |
| Cabbage | Transplant outdoors (spring) | Apr 9 – May 10 |
| Cabbage | Start seeds indoors (fall) | May 26 – Jun 25 |
| Cabbage | Transplant outdoors (fall) | Jun 25 – Jul 26 |
| Leaf lettuce | Sow outdoors (spring) | Apr 9 – Jun 25 |
| Leaf lettuce | Sow outdoors (fall) | Jun 25 – Aug 11 |
| Spinach | Sow outdoors (spring) | Apr 2 – May 16 |
| Spinach | Sow outdoors (fall) | Jul 12 – Aug 16 |
| Radishes | Sow outdoors (spring) | Apr 9 – May 30 |
| Radishes | Sow outdoors (fall) | Jun 25 – Aug 26 |
| Kale | Sow outdoors (spring) | Apr 26 – May 16 |
| Kale | Sow outdoors (fall) | Jun 18 – Jul 26 |
| Carrots | Sow outdoors (spring) | May 10 – Jun 25 |
| Carrots | Sow outdoors (fall) | May 26 – Jul 11 |
| Garlic | Plant outdoors (fall) | Sep 25 – Oct 26 |
Where these dates come from
ZIP code 59910 is matched to the NOAA station Polson, MT, 15.7 km away, at 3,010 ft elevation (44 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Polson, MT (used) | 3,010 ft | May 10 | Oct 5 |
| Skq Dam, MT | 2,730 ft | May 15 | Sep 28 |
| Bigfork 13 S, MT | 2,979 ft | May 1 | Oct 15 |
| Swan Lake, MT | 3,100 ft | May 17 | Sep 19 |
Frost dates near Big Arm
- Elmo, MT 59915 · last May 10, first Oct 5
- Dayton, MT 59914 · last May 1, first Oct 15
- Rollins, MT 59931 · last May 1, first Oct 15
- Polson, MT 59860 · last May 10, first Oct 5
- Proctor, MT 59929 · last May 1, first Oct 15
- Pablo, MT 59855 · last May 10, first Oct 5
- Lakeside, MT 59922 · last May 12, first Sep 25
- Lonepine, MT 59848 · last May 15, first Sep 28
Frequently asked questions
- When is the last frost in Big Arm, MT?
- For ZIP code 59910, the average last spring frost (32°F) is May 10, based on NOAA 1991-2020 climate normals for the Polson, MT weather station. There is a 1-in-10 chance of a frost after May 26.
- When is the first frost in Big Arm, MT?
- The average first fall frost (32°F) is October 5. There is a 1-in-10 chance of frost by September 22, so tender plants are at risk from that point on.
- How long is the growing season in 59910?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 147 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.