Frost dates for 59036Harlowton, MT
The average last spring frost in Harlowton is May 23 and the average first fall frost is September 16, giving a typical growing season of about 113 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 23
- Average first fall frost
- Sep 16
- Growing season
- 113 days
Safer after Jun 6 (1-in-10 risk)
Possible by Sep 1 (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 24 · Jun 9 · Jun 30 | Aug 20 · Sep 4 · Sep 16 | 85 days | 100% |
| Frost / freeze (32°F) | May 12 · May 23 · Jun 6 | Sep 1 · Sep 16 · Sep 28 | 113 days | 100% |
| Hard freeze (28°F) | May 1 · May 12 · May 23 | Sep 12 · Sep 27 · Oct 8 | 137 days | 100% |
Planting calendar for Harlowton
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 – May 27 |
| 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 6 |
| Summer squash | Sow outdoors | Jun 8 – Jul 23 |
| Winter squash & pumpkins | Sow outdoors | Jun 22 – Jul 23 |
| Snap beans | Sow outdoors | Jun 8 – Jun 29 |
| Sweet corn | Sow outdoors | Jun 8 – May 27 |
| 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 17 – May 27 |
| Broccoli | Transplant outdoors (fall) | Jun 16 – Jun 27 |
| Cabbage | Start seeds indoors (spring) | Mar 25 – Apr 22 |
| Cabbage | Transplant outdoors (spring) | Apr 22 – May 23 |
| Cabbage | Start seeds indoors (fall) | May 7 – Jun 6 |
| Cabbage | Transplant outdoors (fall) | Jun 6 – Jul 7 |
| Leaf lettuce | Sow outdoors (spring) | Apr 22 – Jul 8 |
| Leaf lettuce | Sow outdoors (fall) | Jun 6 – Jul 23 |
| Spinach | Sow outdoors (spring) | Apr 15 – May 29 |
| Spinach | Sow outdoors (fall) | Jun 23 – Jul 28 |
| Radishes | Sow outdoors (spring) | Apr 22 – Jun 12 |
| Radishes | Sow outdoors (fall) | Jun 6 – Aug 7 |
| Kale | Sow outdoors (spring) | May 9 – May 29 |
| Kale | Sow outdoors (fall) | May 30 – Jul 7 |
| Carrots | Sow outdoors (spring) | May 23 – Jul 8 |
| Carrots | Sow outdoors (fall) | May 7 – Jun 22 |
| Garlic | Plant outdoors (fall) | Sep 6 – Oct 7 |
Where these dates come from
ZIP code 59036 is matched to the NOAA station Harlowton, MT, 1.3 km away, at 4,222 ft elevation (36 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Harlowton, MT (used) | 4,222 ft | May 23 | Sep 16 |
| Harlowton 11Nw, MT | 4,954 ft | May 30 | Sep 20 |
| Judith Gap, MT | 4,630 ft | Jun 1 | Sep 15 |
| Judith Gap 13 E, MT | 4,791 ft | Jun 3 | Sep 15 |
Frost dates near Harlowton
- Two Dot, MT 59085 · last May 23, first Sep 16
- Shawmut, MT 59078 · last May 23, first Sep 16
- Judith Gap, MT 59453 · last Jun 1, first Sep 15
- Melville, MT 59055 · last Jun 9, first Sep 7
- Buffalo, MT 59418 · last May 28, first Sep 20
- Martinsdale, MT 59053 · last —, first —
- Ryegate, MT 59074 · last May 17, first Sep 23
- Moore, MT 59464 · last May 23, first Sep 21
Frequently asked questions
- When is the last frost in Harlowton, MT?
- For ZIP code 59036, the average last spring frost (32°F) is May 23, based on NOAA 1991-2020 climate normals for the Harlowton, MT weather station. There is a 1-in-10 chance of a frost after June 6.
- When is the first frost in Harlowton, MT?
- The average first fall frost (32°F) is September 16. There is a 1-in-10 chance of frost by September 1, so tender plants are at risk from that point on.
- How long is the growing season in 59036?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 113 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.