Frost dates for 59526Harlem, MT
The average last spring frost in Harlem is May 16 and the average first fall frost is September 21, giving a typical growing season of about 125 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 16
- Average first fall frost
- Sep 21
- Growing season
- 125 days
Safer after May 31 (1-in-10 risk)
Possible by Sep 8 (1-in-10 risk)
Last frost typically in 201 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 16 · May 29 · Jun 13 | Aug 26 · Sep 9 · Sep 23 | 103 days | 100% |
| Frost / freeze (32°F) | May 4 · May 16 · May 31 | Sep 8 · Sep 21 · Oct 2 | 125 days | 100% |
| Hard freeze (28°F) | Apr 24 · May 6 · May 20 | Sep 17 · Sep 29 · Oct 12 | 145 days | 100% |
Planting calendar for Harlem
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 15 – Jun 21 |
| Tomatoes | Transplant outdoors | Jun 1 – Jun 1 |
| Peppers | Start seeds indoors | Apr 15 – May 16 |
| Peppers | Transplant outdoors | Jun 15 – Jul 16 |
| Eggplant | Start seeds indoors | May 2 – May 31 |
| Eggplant | Transplant outdoors | Jun 15 – Jul 16 |
| Cucumbers | Sow outdoors | Jun 15 – Jun 11 |
| Summer squash | Sow outdoors | Jun 1 – Jul 16 |
| Winter squash & pumpkins | Sow outdoors | Jun 15 – Jul 16 |
| Snap beans | Sow outdoors | Jun 1 – Jul 4 |
| Sweet corn | Sow outdoors | Jun 1 – Jun 1 |
| Watermelon & cantaloupe | Sow outdoors | Jun 15 – Jul 16 |
| Okra | Sow outdoors | Jun 8 – Jul 1 |
| Peas | Sow outdoors (spring) | Apr 15 – May 31 |
| Potatoes | Plant outdoors (spring) | Apr 15 – Jun 15 |
| Onions | Start seeds indoors (spring) | Mar 4 – Mar 31 |
| Onions | Transplant outdoors (spring) | May 2 – May 31 |
| Broccoli | Start seeds indoors (spring) | Mar 28 – May 1 |
| Broccoli | Transplant outdoors (spring) | May 2 – May 31 |
| Broccoli | Start seeds indoors (fall) | May 22 – Jun 1 |
| Broccoli | Transplant outdoors (fall) | Jun 21 – Jul 2 |
| Cabbage | Start seeds indoors (spring) | Mar 18 – Apr 15 |
| Cabbage | Transplant outdoors (spring) | Apr 15 – May 16 |
| Cabbage | Start seeds indoors (fall) | May 12 – Jun 11 |
| Cabbage | Transplant outdoors (fall) | Jun 11 – Jul 12 |
| Leaf lettuce | Sow outdoors (spring) | Apr 15 – Jul 1 |
| Leaf lettuce | Sow outdoors (fall) | Jun 11 – Jul 28 |
| Spinach | Sow outdoors (spring) | Apr 8 – May 22 |
| Spinach | Sow outdoors (fall) | Jun 28 – Aug 2 |
| Radishes | Sow outdoors (spring) | Apr 15 – Jun 5 |
| Radishes | Sow outdoors (fall) | Jun 11 – Aug 12 |
| Kale | Sow outdoors (spring) | May 2 – May 22 |
| Kale | Sow outdoors (fall) | Jun 4 – Jul 12 |
| Carrots | Sow outdoors (spring) | May 16 – Jul 1 |
| Carrots | Sow outdoors (fall) | May 12 – Jun 27 |
| Garlic | Plant outdoors (fall) | Sep 11 – Oct 12 |
Where these dates come from
ZIP code 59526 is matched to the NOAA station Harlem, MT, 2.1 km away, at 2,371 ft elevation (11 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Harlem, MT (used) | 2,371 ft | May 16 | Sep 21 |
| Ft Belknap 2 Sw, MT | 2,527 ft | May 16 | Sep 22 |
| Chinook, MT | 2,420 ft | May 14 | Sep 23 |
| Harlem 20S, MT | 2,695 ft | May 24 | Sep 22 |
Frost dates near Harlem
- Zurich, MT 59547 · last May 14, first Sep 23
- Chinook, MT 59523 · last May 14, first Sep 23
- Hogeland, MT 59529 · last May 19, first Sep 21
- Dodson, MT 59524 · last May 10, first Sep 29
- Turner, MT 59542 · last May 19, first Sep 21
- Hays, MT 59527 · last May 18, first Sep 23
- Havre, MT 59501 · last May 15, first Sep 23
- Malta, MT 59538 · last May 10, first Sep 29
Frequently asked questions
- When is the last frost in Harlem, MT?
- For ZIP code 59526, the average last spring frost (32°F) is May 16, based on NOAA 1991-2020 climate normals for the Harlem, MT weather station. There is a 1-in-10 chance of a frost after May 31.
- When is the first frost in Harlem, MT?
- The average first fall frost (32°F) is September 21. 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 59526?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 125 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.