Frost dates for 59527Hays, MT
The average last spring frost in Hays is May 18 and the average first fall frost is September 23, giving a typical growing season of about 126 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 18
- Average first fall frost
- Sep 23
- Growing season
- 126 days
Safer after Jun 1 (1-in-10 risk)
Possible by Sep 7 (1-in-10 risk)
Last frost typically in 203 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 18 · May 31 · Jun 20 | Aug 26 · Sep 12 · Sep 26 | 101 days | 100% |
| Frost / freeze (32°F) | May 4 · May 18 · Jun 1 | Sep 7 · Sep 23 · Oct 5 | 126 days | 100% |
| Hard freeze (28°F) | Apr 20 · May 5 · May 20 | Sep 17 · Oct 2 · Oct 17 | 149 days | 100% |
Planting calendar for Hays
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 17 – Jun 23 |
| Tomatoes | Transplant outdoors | Jun 3 – Jun 3 |
| Peppers | Start seeds indoors | Apr 17 – May 18 |
| Peppers | Transplant outdoors | Jun 17 – Jul 18 |
| Eggplant | Start seeds indoors | May 4 – Jun 2 |
| Eggplant | Transplant outdoors | Jun 17 – Jul 18 |
| Cucumbers | Sow outdoors | Jun 17 – Jun 13 |
| Summer squash | Sow outdoors | Jun 3 – Jul 18 |
| Winter squash & pumpkins | Sow outdoors | Jun 17 – Jul 18 |
| Snap beans | Sow outdoors | Jun 3 – Jul 6 |
| Sweet corn | Sow outdoors | Jun 3 – Jun 3 |
| Watermelon & cantaloupe | Sow outdoors | Jun 17 – Jul 18 |
| Okra | Sow outdoors | Jun 10 – Jul 3 |
| Peas | Sow outdoors (spring) | Apr 17 – Jun 2 |
| Potatoes | Plant outdoors (spring) | Apr 17 – Jun 17 |
| Onions | Start seeds indoors (spring) | Mar 6 – Apr 2 |
| Onions | Transplant outdoors (spring) | May 4 – Jun 2 |
| Broccoli | Start seeds indoors (spring) | Mar 30 – May 3 |
| Broccoli | Transplant outdoors (spring) | May 4 – Jun 2 |
| Broccoli | Start seeds indoors (fall) | May 24 – Jun 3 |
| Broccoli | Transplant outdoors (fall) | Jun 23 – Jul 4 |
| Cabbage | Start seeds indoors (spring) | Mar 20 – Apr 17 |
| Cabbage | Transplant outdoors (spring) | Apr 17 – May 18 |
| Cabbage | Start seeds indoors (fall) | May 14 – Jun 13 |
| Cabbage | Transplant outdoors (fall) | Jun 13 – Jul 14 |
| Leaf lettuce | Sow outdoors (spring) | Apr 17 – Jul 3 |
| Leaf lettuce | Sow outdoors (fall) | Jun 13 – Jul 30 |
| Spinach | Sow outdoors (spring) | Apr 10 – May 24 |
| Spinach | Sow outdoors (fall) | Jun 30 – Aug 4 |
| Radishes | Sow outdoors (spring) | Apr 17 – Jun 7 |
| Radishes | Sow outdoors (fall) | Jun 13 – Aug 14 |
| Kale | Sow outdoors (spring) | May 4 – May 24 |
| Kale | Sow outdoors (fall) | Jun 6 – Jul 14 |
| Carrots | Sow outdoors (spring) | May 18 – Jul 3 |
| Carrots | Sow outdoors (fall) | May 14 – Jun 29 |
| Garlic | Plant outdoors (fall) | Sep 13 – Oct 14 |
Where these dates come from
ZIP code 59527 is matched to the NOAA station Zortman, MT, 14.9 km away, at 4,035 ft elevation (505 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Zortman, MT (used) | 4,035 ft | May 18 | Sep 23 |
| Harlem 20S, MT | 2,695 ft | May 24 | Sep 22 |
| Chinook 35Se, MT | 3,360 ft | May 23 | Sep 23 |
| Sand Creek, MT | 2,910 ft | May 12 | Sep 27 |
Frost dates near Hays
- Zortman, MT 59546 · last May 12, first Sep 27
- Lloyd, MT 59535 · last May 23, first Sep 23
- Dodson, MT 59524 · last May 10, first Sep 29
- Winifred, MT 59489 · last May 16, first Sep 23
- Harlem, MT 59526 · last May 16, first Sep 21
- Roy, MT 59471 · last May 14, first Sep 24
- Zurich, MT 59547 · last May 14, first Sep 23
- Malta, MT 59538 · last May 10, first Sep 29
Frequently asked questions
- When is the last frost in Hays, MT?
- For ZIP code 59527, the average last spring frost (32°F) is May 18, based on NOAA 1991-2020 climate normals for the Zortman, MT weather station. There is a 1-in-10 chance of a frost after June 1.
- When is the first frost in Hays, MT?
- The average first fall frost (32°F) is September 23. There is a 1-in-10 chance of frost by September 7, so tender plants are at risk from that point on.
- How long is the growing season in 59527?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 126 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.