Frost dates for 59406Great Falls, MT
The average last spring frost in Great Falls is May 23 and the average first fall frost is September 23, giving a typical growing season of about 120 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 23
- Average first fall frost
- Sep 23
- Growing season
- 120 days
Safer after Jun 9 (1-in-10 risk)
Possible by Sep 8 (1-in-10 risk)
Last frost typically in 208 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 24 · Jun 9 · Jul 3 | Aug 26 · Sep 11 · Sep 24 | 92 days | 100% |
| Frost / freeze (32°F) | May 10 · May 23 · Jun 9 | Sep 8 · Sep 23 · Oct 4 | 120 days | 100% |
| Hard freeze (28°F) | Apr 28 · May 9 · May 24 | Sep 19 · Oct 1 · Oct 16 | 145 days | 100% |
Planting calendar for Great Falls
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 22 – Jun 28 |
| Tomatoes | Transplant outdoors | Jun 8 – Jun 3 |
| Peppers | Start seeds indoors | Apr 22 – May 23 |
| Peppers | Transplant outdoors | Jun 22 – Jul 23 |
| Eggplant | Start seeds indoors | May 9 – Jun 7 |
| Eggplant | Transplant outdoors | Jun 22 – Jul 23 |
| Cucumbers | Sow outdoors | Jun 22 – Jun 13 |
| Summer squash | Sow outdoors | Jun 8 – Jul 23 |
| Winter squash & pumpkins | Sow outdoors | Jun 22 – Jul 23 |
| Snap beans | Sow outdoors | Jun 8 – Jul 6 |
| Sweet corn | Sow outdoors | Jun 8 – Jun 3 |
| Watermelon & cantaloupe | Sow outdoors | Jun 22 – Jul 23 |
| Okra | Sow outdoors | Jun 15 – Jul 8 |
| Peas | Sow outdoors (spring) | Apr 22 – Jun 7 |
| Potatoes | Plant outdoors (spring) | Apr 22 – Jun 22 |
| Onions | Start seeds indoors (spring) | Mar 11 – Apr 7 |
| Onions | Transplant outdoors (spring) | May 9 – Jun 7 |
| Broccoli | Start seeds indoors (spring) | Apr 4 – May 8 |
| Broccoli | Transplant outdoors (spring) | May 9 – Jun 7 |
| Broccoli | Start seeds indoors (fall) | May 24 – Jun 3 |
| Broccoli | Transplant outdoors (fall) | Jun 23 – Jul 4 |
| Cabbage | Start seeds indoors (spring) | Mar 25 – Apr 22 |
| Cabbage | Transplant outdoors (spring) | Apr 22 – May 23 |
| Cabbage | Start seeds indoors (fall) | May 14 – Jun 13 |
| Cabbage | Transplant outdoors (fall) | Jun 13 – Jul 14 |
| Leaf lettuce | Sow outdoors (spring) | Apr 22 – Jul 8 |
| Leaf lettuce | Sow outdoors (fall) | Jun 13 – Jul 30 |
| Spinach | Sow outdoors (spring) | Apr 15 – May 29 |
| Spinach | Sow outdoors (fall) | Jun 30 – Aug 4 |
| Radishes | Sow outdoors (spring) | Apr 22 – Jun 12 |
| Radishes | Sow outdoors (fall) | Jun 13 – Aug 14 |
| Kale | Sow outdoors (spring) | May 9 – May 29 |
| Kale | Sow outdoors (fall) | Jun 6 – Jul 14 |
| Carrots | Sow outdoors (spring) | May 23 – Jul 8 |
| Carrots | Sow outdoors (fall) | May 14 – Jun 29 |
| Garlic | Plant outdoors (fall) | Sep 13 – Oct 14 |
Where these dates come from
ZIP code 59406 is matched to the NOAA station Carter 14 W, MT, 19.2 km away, at 3,450 ft elevation (41 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Carter 14 W, MT (used) | 3,450 ft | May 23 | Sep 23 |
| Great Falls 16St, MT | 3,505 ft | May 6 | Oct 1 |
| Great Falls Intl Ap, MT | 3,664 ft | May 19 | Sep 24 |
| Great Falls Wfo, MT | 3,705 ft | May 12 | Sep 28 |
Frost dates near Great Falls
- Floweree, MT 59440 · last May 23, first Sep 23
- Black Eagle, MT 59414 · last May 19, first Sep 24
- Great Falls, MT 59401 · last May 19, first Sep 24
- Malmstrom Afb, MT 59402 · last May 19, first Sep 24
- Sand Coulee, MT 59472 · last May 19, first Sep 24
- Vaughn, MT 59487 · last Jun 2, first Sep 10
- Carter, MT 59420 · last May 23, first Sep 23
- Highwood, MT 59450 · last May 7, first Oct 2
Frequently asked questions
- When is the last frost in Great Falls, MT?
- For ZIP code 59406, the average last spring frost (32°F) is May 23, based on NOAA 1991-2020 climate normals for the Carter 14 W, MT weather station. There is a 1-in-10 chance of a frost after June 9.
- When is the first frost in Great Falls, MT?
- The average first fall frost (32°F) is September 23. There is a 1-in-10 chance of frost by September 8, so tender plants are at risk from that point on.
- How long is the growing season in 59406?
- 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.