Frost dates for 59483Sun River, MT
The average last spring frost in Sun River is June 2 and the average first fall frost is September 10, giving a typical growing season of about 96 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Jun 2
- Average first fall frost
- Sep 10
- Growing season
- 96 days
Safer after Jun 21 (1-in-10 risk)
Possible by Aug 25 (1-in-10 risk)
Last frost typically in 218 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) | — | — | 62 days | 100% |
| Frost / freeze (32°F) | May 18 · Jun 2 · Jun 21 | Aug 25 · Sep 10 · Sep 25 | 96 days | 100% |
| Hard freeze (28°F) | May 5 · May 18 · May 31 | Sep 6 · Sep 22 · Oct 7 | 127 days | 100% |
Planting calendar for Sun River
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 | May 2 – Jul 8 |
| Tomatoes | Transplant outdoors | Jun 18 – May 21 |
| Peppers | Start seeds indoors | May 2 – Jun 2 |
| Peppers | Transplant outdoors | Jul 2 – Aug 2 |
| Eggplant | Start seeds indoors | May 19 – Jun 17 |
| Eggplant | Transplant outdoors | Jul 2 – Aug 2 |
| Cucumbers | Sow outdoors | Jul 2 – May 31 |
| Summer squash | Sow outdoors | Jun 18 – Aug 2 |
| Winter squash & pumpkins | Sow outdoors | Jul 2 – Aug 2 |
| Snap beans | Sow outdoors | Jun 18 – Jun 23 |
| Sweet corn | Sow outdoors | Jun 18 – May 21 |
| Watermelon & cantaloupe | Sow outdoors | Jul 2 – Aug 2 |
| Okra | Sow outdoors | Jun 25 – Jul 18 |
| Peas | Sow outdoors (spring) | May 2 – Jun 17 |
| Potatoes | Plant outdoors (spring) | May 2 – Jul 2 |
| Onions | Start seeds indoors (spring) | Mar 21 – Apr 17 |
| Onions | Transplant outdoors (spring) | May 19 – Jun 17 |
| Broccoli | Start seeds indoors (spring) | Apr 14 – May 18 |
| Broccoli | Transplant outdoors (spring) | May 19 – Jun 17 |
| Broccoli | Start seeds indoors (fall) | May 11 – May 21 |
| Broccoli | Transplant outdoors (fall) | Jun 10 – Jun 21 |
| Cabbage | Start seeds indoors (spring) | Apr 4 – May 2 |
| Cabbage | Transplant outdoors (spring) | May 2 – Jun 2 |
| Cabbage | Start seeds indoors (fall) | May 1 – May 31 |
| Cabbage | Transplant outdoors (fall) | May 31 – Jul 1 |
| Leaf lettuce | Sow outdoors (spring) | May 2 – Jul 18 |
| Leaf lettuce | Sow outdoors (fall) | May 31 – Jul 17 |
| Spinach | Sow outdoors (spring) | Apr 25 – Jun 8 |
| Spinach | Sow outdoors (fall) | Jun 17 – Jul 22 |
| Radishes | Sow outdoors (spring) | May 2 – Jun 22 |
| Radishes | Sow outdoors (fall) | May 31 – Aug 1 |
| Kale | Sow outdoors (spring) | May 19 – Jun 8 |
| Kale | Sow outdoors (fall) | May 24 – Jul 1 |
| Carrots | Sow outdoors (spring) | Jun 2 – Jul 18 |
| Carrots | Sow outdoors (fall) | May 1 – Jun 16 |
| Garlic | Plant outdoors (fall) | Aug 31 – Oct 1 |
Where these dates come from
ZIP code 59483 is matched to the NOAA station Sun Rvr 4 S, MT, 1.1 km away, at 3,600 ft elevation (29 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Sun Rvr 4 S, MT (used) | 3,600 ft | Jun 2 | Sep 10 |
| Fairfield, MT | 3,983 ft | May 13 | Sep 27 |
| Great Falls Wfo, MT | 3,705 ft | May 12 | Sep 28 |
| Great Falls Intl Ap, MT | 3,664 ft | May 19 | Sep 24 |
Frost dates near Sun River
- Fort Shaw, MT 59443 · last Jun 2, first Sep 10
- Simms, MT 59477 · last Jun 2, first Sep 10
- Vaughn, MT 59487 · last Jun 2, first Sep 10
- Ulm, MT 59485 · last Jun 2, first Sep 10
- Cascade, MT 59421 · last May 21, first Sep 19
- Power, MT 59468 · last Jun 2, first Sep 10
- Fairfield, MT 59436 · last May 13, first Sep 27
- Great Falls, MT 59404 · last May 19, first Sep 24
Frequently asked questions
- When is the last frost in Sun River, MT?
- For ZIP code 59483, the average last spring frost (32°F) is June 2, based on NOAA 1991-2020 climate normals for the Sun Rvr 4 S, MT weather station. There is a 1-in-10 chance of a frost after June 21.
- When is the first frost in Sun River, MT?
- The average first fall frost (32°F) is September 10. There is a 1-in-10 chance of frost by August 25, so tender plants are at risk from that point on.
- How long is the growing season in 59483?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 96 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.