Frost dates for 59231Saint Marie, MT
The average last spring frost in Saint Marie is May 13 and the average first fall frost is September 27, giving a typical growing season of about 134 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 13
- Average first fall frost
- Sep 27
- Growing season
- 134 days
Safer after May 26 (1-in-10 risk)
Possible by Sep 13 (1-in-10 risk)
Last frost typically in 191 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 12 · May 24 · Jun 4 | Sep 5 · Sep 19 · Sep 30 | 117 days | 100% |
| Frost / freeze (32°F) | May 2 · May 13 · May 26 | Sep 13 · Sep 27 · Oct 9 | 134 days | 100% |
| Hard freeze (28°F) | Apr 19 · May 3 · May 16 | Sep 22 · Oct 5 · Oct 21 | 154 days | 100% |
Planting calendar for Saint Marie
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 12 – Jun 18 |
| Tomatoes | Transplant outdoors | May 29 – Jun 7 |
| Peppers | Start seeds indoors | Apr 12 – May 13 |
| Peppers | Transplant outdoors | Jun 12 – Jul 13 |
| Eggplant | Start seeds indoors | Apr 29 – May 28 |
| Eggplant | Transplant outdoors | Jun 12 – Jul 13 |
| Cucumbers | Sow outdoors | Jun 12 – Jun 17 |
| Summer squash | Sow outdoors | May 29 – Jul 13 |
| Winter squash & pumpkins | Sow outdoors | Jun 12 – Jul 13 |
| Snap beans | Sow outdoors | May 29 – Jul 10 |
| Sweet corn | Sow outdoors | May 29 – Jun 7 |
| Watermelon & cantaloupe | Sow outdoors | Jun 12 – Jul 13 |
| Okra | Sow outdoors | Jun 5 – Jun 28 |
| Peas | Sow outdoors (spring) | Apr 12 – May 28 |
| Potatoes | Plant outdoors (spring) | Apr 12 – Jun 12 |
| Onions | Start seeds indoors (spring) | Mar 1 – Mar 28 |
| Onions | Transplant outdoors (spring) | Apr 29 – May 28 |
| Broccoli | Start seeds indoors (spring) | Mar 25 – Apr 28 |
| Broccoli | Transplant outdoors (spring) | Apr 29 – May 28 |
| Broccoli | Start seeds indoors (fall) | May 28 – Jun 7 |
| Broccoli | Transplant outdoors (fall) | Jun 27 – Jul 8 |
| Cabbage | Start seeds indoors (spring) | Mar 15 – Apr 12 |
| Cabbage | Transplant outdoors (spring) | Apr 12 – May 13 |
| Cabbage | Start seeds indoors (fall) | May 18 – Jun 17 |
| Cabbage | Transplant outdoors (fall) | Jun 17 – Jul 18 |
| Leaf lettuce | Sow outdoors (spring) | Apr 12 – Jun 28 |
| Leaf lettuce | Sow outdoors (fall) | Jun 17 – Aug 3 |
| Spinach | Sow outdoors (spring) | Apr 5 – May 19 |
| Spinach | Sow outdoors (fall) | Jul 4 – Aug 8 |
| Radishes | Sow outdoors (spring) | Apr 12 – Jun 2 |
| Radishes | Sow outdoors (fall) | Jun 17 – Aug 18 |
| Kale | Sow outdoors (spring) | Apr 29 – May 19 |
| Kale | Sow outdoors (fall) | Jun 10 – Jul 18 |
| Carrots | Sow outdoors (spring) | May 13 – Jun 28 |
| Carrots | Sow outdoors (fall) | May 18 – Jul 3 |
| Garlic | Plant outdoors (fall) | Sep 17 – Oct 18 |
Where these dates come from
ZIP code 59231 is matched to the NOAA station St Marie, MT, 2.2 km away, at 2,756 ft elevation (3 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| St Marie, MT (used) | 2,756 ft | May 13 | Sep 27 |
| Glasgow Intl Ap, MT | 2,285 ft | May 6 | Sep 30 |
| Glasgow #2, MT | 2,090 ft | May 3 | Oct 1 |
| Nashua #2, MT | 2,067 ft | May 12 | Sep 24 |
Frost dates near Saint Marie
- Glasgow, MT 59230 · last May 6, first Sep 30
- Larslan, MT 59244 · last Jun 5, first Sep 2
- Vandalia, MT 59273 · last May 3, first Oct 1
- Nashua, MT 59248 · last May 12, first Sep 24
- Hinsdale, MT 59241 · last May 15, first Sep 23
- Frazer, MT 59225 · last May 13, first Sep 27
- Richland, MT 59260 · last Jun 5, first Sep 2
- Fort Peck, MT 59223 · last May 8, first Oct 1
Frequently asked questions
- When is the last frost in Saint Marie, MT?
- For ZIP code 59231, the average last spring frost (32°F) is May 13, based on NOAA 1991-2020 climate normals for the St Marie, MT weather station. There is a 1-in-10 chance of a frost after May 26.
- When is the first frost in Saint Marie, MT?
- The average first fall frost (32°F) is September 27. There is a 1-in-10 chance of frost by September 13, so tender plants are at risk from that point on.
- How long is the growing season in 59231?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 134 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.