Frost dates for 59421Cascade, MT
The average last spring frost in Cascade is May 21 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 21
- Average first fall frost
- Sep 19
- Growing season
- 120 days
Safer after Jun 6 (1-in-10 risk)
Possible by Sep 2 (1-in-10 risk)
Last frost typically in 199 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 22 · Jun 8 · Jun 27 | Aug 18 · Sep 3 · Sep 21 | 88 days | 100% |
| Frost / freeze (32°F) | May 5 · May 21 · Jun 6 | Sep 2 · Sep 19 · Oct 2 | 120 days | 100% |
| Hard freeze (28°F) | Apr 22 · May 7 · May 22 | Sep 13 · Oct 1 · Oct 16 | 145 days | 100% |
Planting calendar for Cascade
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 20 – Jun 26 |
| Tomatoes | Transplant outdoors | Jun 6 – May 30 |
| Peppers | Start seeds indoors | Apr 20 – May 21 |
| Peppers | Transplant outdoors | Jun 20 – Jul 21 |
| Eggplant | Start seeds indoors | May 7 – Jun 5 |
| Eggplant | Transplant outdoors | Jun 20 – Jul 21 |
| Cucumbers | Sow outdoors | Jun 20 – Jun 9 |
| Summer squash | Sow outdoors | Jun 6 – Jul 21 |
| Winter squash & pumpkins | Sow outdoors | Jun 20 – Jul 21 |
| Snap beans | Sow outdoors | Jun 6 – Jul 2 |
| Sweet corn | Sow outdoors | Jun 6 – May 30 |
| Watermelon & cantaloupe | Sow outdoors | Jun 20 – Jul 21 |
| Okra | Sow outdoors | Jun 13 – Jul 6 |
| Peas | Sow outdoors (spring) | Apr 20 – Jun 5 |
| Potatoes | Plant outdoors (spring) | Apr 20 – Jun 20 |
| Onions | Start seeds indoors (spring) | Mar 9 – Apr 5 |
| Onions | Transplant outdoors (spring) | May 7 – Jun 5 |
| Broccoli | Start seeds indoors (spring) | Apr 2 – May 6 |
| Broccoli | Transplant outdoors (spring) | May 7 – Jun 5 |
| Broccoli | Start seeds indoors (fall) | May 20 – May 30 |
| Broccoli | Transplant outdoors (fall) | Jun 19 – Jun 30 |
| Cabbage | Start seeds indoors (spring) | Mar 23 – Apr 20 |
| Cabbage | Transplant outdoors (spring) | Apr 20 – May 21 |
| Cabbage | Start seeds indoors (fall) | May 10 – Jun 9 |
| Cabbage | Transplant outdoors (fall) | Jun 9 – Jul 10 |
| Leaf lettuce | Sow outdoors (spring) | Apr 20 – Jul 6 |
| Leaf lettuce | Sow outdoors (fall) | Jun 9 – Jul 26 |
| Spinach | Sow outdoors (spring) | Apr 13 – May 27 |
| Spinach | Sow outdoors (fall) | Jun 26 – Jul 31 |
| Radishes | Sow outdoors (spring) | Apr 20 – Jun 10 |
| Radishes | Sow outdoors (fall) | Jun 9 – Aug 10 |
| Kale | Sow outdoors (spring) | May 7 – May 27 |
| Kale | Sow outdoors (fall) | Jun 2 – Jul 10 |
| Carrots | Sow outdoors (spring) | May 21 – Jul 6 |
| Carrots | Sow outdoors (fall) | May 10 – Jun 25 |
| Garlic | Plant outdoors (fall) | Sep 9 – Oct 10 |
Where these dates come from
ZIP code 59421 is matched to the NOAA station Cascade 5 S, MT, 8.1 km away, at 3,360 ft elevation (761 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Cascade 5 S, MT (used) | 3,360 ft | May 21 | Sep 19 |
| Sun Rvr 4 S, MT | 3,600 ft | Jun 2 | Sep 10 |
| Adel, MT | 5,017 ft | Jun 4 | Sep 12 |
| Great Falls Wfo, MT | 3,705 ft | May 12 | Sep 28 |
Frost dates near Cascade
- Ulm, MT 59485 · last Jun 2, first Sep 10
- Sun River, MT 59483 · last Jun 2, first Sep 10
- 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
- Great Falls, MT 59404 · last May 19, first Sep 24
- Malmstrom Afb, MT 59402 · last May 19, first Sep 24
- Wolf Creek, MT 59648 · last May 21, first Sep 15
Frequently asked questions
- When is the last frost in Cascade, MT?
- For ZIP code 59421, the average last spring frost (32°F) is May 21, based on NOAA 1991-2020 climate normals for the Cascade 5 S, MT weather station. There is a 1-in-10 chance of a frost after June 6.
- When is the first frost in Cascade, MT?
- The average first fall frost (32°F) is September 19. There is a 1-in-10 chance of frost by September 2, so tender plants are at risk from that point on.
- How long is the growing season in 59421?
- 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.