Frost dates for 59865Saint Ignatius, MT
The average last spring frost in Saint Ignatius is May 12 and the average first fall frost is October 2, giving a typical growing season of about 142 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 12
- Average first fall frost
- Oct 2
- Growing season
- 142 days
Safer after Jun 1 (1-in-10 risk)
Possible by Sep 19 (1-in-10 risk)
Last frost typically in 197 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 · Jun 1 · Jun 24 | Sep 4 · Sep 22 · Oct 4 | 110 days | 100% |
| Frost / freeze (32°F) | Apr 28 · May 12 · Jun 1 | Sep 19 · Oct 2 · Oct 14 | 142 days | 100% |
| Hard freeze (28°F) | Apr 9 · Apr 30 · May 17 | Sep 29 · Oct 12 · Oct 27 | 166 days | 100% |
Planting calendar for Saint Ignatius
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 11 – Jun 17 |
| Tomatoes | Transplant outdoors | May 28 – Jun 12 |
| Peppers | Start seeds indoors | Apr 11 – May 12 |
| Peppers | Transplant outdoors | Jun 11 – Jul 12 |
| Eggplant | Start seeds indoors | Apr 28 – May 27 |
| Eggplant | Transplant outdoors | Jun 11 – Jul 12 |
| Cucumbers | Sow outdoors | Jun 11 – Jun 22 |
| Summer squash | Sow outdoors | May 28 – Jul 12 |
| Winter squash & pumpkins | Sow outdoors | Jun 11 – Jul 12 |
| Snap beans | Sow outdoors | May 28 – Jul 15 |
| Sweet corn | Sow outdoors | May 28 – Jun 12 |
| Watermelon & cantaloupe | Sow outdoors | Jun 11 – Jul 12 |
| Okra | Sow outdoors | Jun 4 – Jun 27 |
| Peas | Sow outdoors (spring) | Apr 11 – May 27 |
| Potatoes | Plant outdoors (spring) | Apr 11 – Jun 11 |
| Onions | Start seeds indoors (spring) | Feb 28 – Mar 27 |
| Onions | Transplant outdoors (spring) | Apr 28 – May 27 |
| Broccoli | Start seeds indoors (spring) | Mar 24 – Apr 27 |
| Broccoli | Transplant outdoors (spring) | Apr 28 – May 27 |
| Broccoli | Start seeds indoors (fall) | Jun 2 – Jun 12 |
| Broccoli | Transplant outdoors (fall) | Jul 2 – Jul 13 |
| Cabbage | Start seeds indoors (spring) | Mar 14 – Apr 11 |
| Cabbage | Transplant outdoors (spring) | Apr 11 – May 12 |
| Cabbage | Start seeds indoors (fall) | May 23 – Jun 22 |
| Cabbage | Transplant outdoors (fall) | Jun 22 – Jul 23 |
| Leaf lettuce | Sow outdoors (spring) | Apr 11 – Jun 27 |
| Leaf lettuce | Sow outdoors (fall) | Jun 22 – Aug 8 |
| Spinach | Sow outdoors (spring) | Apr 4 – May 18 |
| Spinach | Sow outdoors (fall) | Jul 9 – Aug 13 |
| Radishes | Sow outdoors (spring) | Apr 11 – Jun 1 |
| Radishes | Sow outdoors (fall) | Jun 22 – Aug 23 |
| Kale | Sow outdoors (spring) | Apr 28 – May 18 |
| Kale | Sow outdoors (fall) | Jun 15 – Jul 23 |
| Carrots | Sow outdoors (spring) | May 12 – Jun 27 |
| Carrots | Sow outdoors (fall) | May 23 – Jul 8 |
| Garlic | Plant outdoors (fall) | Sep 22 – Oct 23 |
Where these dates come from
ZIP code 59865 is matched to the NOAA station Saint Ignatius, MT, 2.4 km away, at 2,915 ft elevation (84 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Saint Ignatius, MT (used) | 2,915 ft | May 12 | Oct 2 |
| Lindbergh Lake, MT | 4,320 ft | May 20 | Sep 22 |
| Polson, MT | 3,010 ft | May 10 | Oct 5 |
| Skq Dam, MT | 2,730 ft | May 15 | Sep 28 |
Frost dates near Saint Ignatius
- Ravalli, MT 59863 · last May 12, first Oct 2
- Charlo, MT 59824 · last May 12, first Oct 2
- Arlee, MT 59821 · last May 12, first Oct 2
- Dixon, MT 59831 · last May 12, first Oct 2
- Ronan, MT 59864 · last May 10, first Oct 5
- Pablo, MT 59855 · last May 10, first Oct 5
- Condon, MT 59826 · last May 20, first Sep 22
- Frenchtown, MT 59834 · last May 10, first Oct 1
Frequently asked questions
- When is the last frost in Saint Ignatius, MT?
- For ZIP code 59865, the average last spring frost (32°F) is May 12, based on NOAA 1991-2020 climate normals for the Saint Ignatius, MT weather station. There is a 1-in-10 chance of a frost after June 1.
- When is the first frost in Saint Ignatius, MT?
- The average first fall frost (32°F) is October 2. There is a 1-in-10 chance of frost by September 19, so tender plants are at risk from that point on.
- How long is the growing season in 59865?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 142 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.