Frost dates for 59442Fort Benton, MT
The average last spring frost in Fort Benton is May 20 and the average first fall frost is September 19, giving a typical growing season of about 120 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 20
- Average first fall frost
- Sep 19
- Growing season
- 120 days
Safer after Jun 3 (1-in-10 risk)
Possible by Sep 4 (1-in-10 risk)
Last frost typically in 198 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 20 · Jun 2 · Jun 21 | Aug 22 · Sep 7 · Sep 21 | 94 days | 100% |
| Frost / freeze (32°F) | May 8 · May 20 · Jun 3 | Sep 4 · Sep 19 · Oct 2 | 120 days | 100% |
| Hard freeze (28°F) | Apr 25 · May 9 · May 21 | Sep 16 · Sep 29 · Oct 11 | 143 days | 100% |
Planting calendar for Fort Benton
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 19 – Jun 25 |
| Tomatoes | Transplant outdoors | Jun 5 – May 30 |
| Peppers | Start seeds indoors | Apr 19 – May 20 |
| Peppers | Transplant outdoors | Jun 19 – Jul 20 |
| Eggplant | Start seeds indoors | May 6 – Jun 4 |
| Eggplant | Transplant outdoors | Jun 19 – Jul 20 |
| Cucumbers | Sow outdoors | Jun 19 – Jun 9 |
| Summer squash | Sow outdoors | Jun 5 – Jul 20 |
| Winter squash & pumpkins | Sow outdoors | Jun 19 – Jul 20 |
| Snap beans | Sow outdoors | Jun 5 – Jul 2 |
| Sweet corn | Sow outdoors | Jun 5 – May 30 |
| Watermelon & cantaloupe | Sow outdoors | Jun 19 – Jul 20 |
| Okra | Sow outdoors | Jun 12 – Jul 5 |
| Peas | Sow outdoors (spring) | Apr 19 – Jun 4 |
| Potatoes | Plant outdoors (spring) | Apr 19 – Jun 19 |
| Onions | Start seeds indoors (spring) | Mar 8 – Apr 4 |
| Onions | Transplant outdoors (spring) | May 6 – Jun 4 |
| Broccoli | Start seeds indoors (spring) | Apr 1 – May 5 |
| Broccoli | Transplant outdoors (spring) | May 6 – Jun 4 |
| Broccoli | Start seeds indoors (fall) | May 20 – May 30 |
| Broccoli | Transplant outdoors (fall) | Jun 19 – Jun 30 |
| Cabbage | Start seeds indoors (spring) | Mar 22 – Apr 19 |
| Cabbage | Transplant outdoors (spring) | Apr 19 – May 20 |
| Cabbage | Start seeds indoors (fall) | May 10 – Jun 9 |
| Cabbage | Transplant outdoors (fall) | Jun 9 – Jul 10 |
| Leaf lettuce | Sow outdoors (spring) | Apr 19 – Jul 5 |
| Leaf lettuce | Sow outdoors (fall) | Jun 9 – Jul 26 |
| Spinach | Sow outdoors (spring) | Apr 12 – May 26 |
| Spinach | Sow outdoors (fall) | Jun 26 – Jul 31 |
| Radishes | Sow outdoors (spring) | Apr 19 – Jun 9 |
| Radishes | Sow outdoors (fall) | Jun 9 – Aug 10 |
| Kale | Sow outdoors (spring) | May 6 – May 26 |
| Kale | Sow outdoors (fall) | Jun 2 – Jul 10 |
| Carrots | Sow outdoors (spring) | May 20 – Jul 5 |
| Carrots | Sow outdoors (fall) | May 10 – Jun 25 |
| Garlic | Plant outdoors (fall) | Sep 9 – Oct 10 |
Where these dates come from
ZIP code 59442 is matched to the NOAA station Loma, MT, 7.8 km away, at 2,578 ft elevation (303 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Loma, MT (used) | 2,578 ft | May 20 | Sep 19 |
| Ft Benton, MT | 2,649 ft | May 15 | Sep 22 |
| Highwood 7 Ne, MT | 3,600 ft | May 7 | Oct 2 |
| Rudyard 19S, MT | 2,878 ft | May 23 | Sep 19 |
Frost dates near Fort Benton
- Loma, MT 59460 · last May 20, first Sep 19
- Carter, MT 59420 · last May 23, first Sep 23
- Highwood, MT 59450 · last May 7, first Oct 2
- Geraldine, MT 59446 · last May 14, first Sep 26
- Big Sandy, MT 59520 · last May 17, first Sep 25
- Floweree, MT 59440 · last May 23, first Sep 23
- Great Falls, MT 59406 · last May 23, first Sep 23
- Belt, MT 59412 · last May 22, first Sep 23
Frequently asked questions
- When is the last frost in Fort Benton, MT?
- For ZIP code 59442, the average last spring frost (32°F) is May 20, based on NOAA 1991-2020 climate normals for the Loma, MT weather station. There is a 1-in-10 chance of a frost after June 3.
- When is the first frost in Fort Benton, MT?
- The average first fall frost (32°F) is September 19. There is a 1-in-10 chance of frost by September 4, so tender plants are at risk from that point on.
- How long is the growing season in 59442?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 120 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.