Frost dates for 59336Ismay, MT
The average last spring frost in Ismay is May 22 and the average first fall frost is September 15, giving a typical growing season of about 117 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 22
- Average first fall frost
- Sep 15
- Growing season
- 117 days
Safer after Jun 7 (1-in-10 risk)
Possible by Sep 2 (1-in-10 risk)
Last frost typically in 200 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 · Jun 2 · Jun 22 | Aug 22 · Sep 6 · Sep 21 | 95 days | 100% |
| Frost / freeze (32°F) | May 9 · May 22 · Jun 7 | Sep 2 · Sep 15 · Oct 1 | 117 days | 100% |
| Hard freeze (28°F) | Apr 28 · May 11 · May 28 | Sep 10 · Sep 25 · Oct 8 | 137 days | 100% |
Planting calendar for Ismay
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 21 – Jun 27 |
| Tomatoes | Transplant outdoors | Jun 7 – May 26 |
| Peppers | Start seeds indoors | Apr 21 – May 22 |
| Peppers | Transplant outdoors | Jun 21 – Jul 22 |
| Eggplant | Start seeds indoors | May 8 – Jun 6 |
| Eggplant | Transplant outdoors | Jun 21 – Jul 22 |
| Cucumbers | Sow outdoors | Jun 21 – Jun 5 |
| Summer squash | Sow outdoors | Jun 7 – Jul 22 |
| Winter squash & pumpkins | Sow outdoors | Jun 21 – Jul 22 |
| Snap beans | Sow outdoors | Jun 7 – Jun 28 |
| Sweet corn | Sow outdoors | Jun 7 – May 26 |
| Watermelon & cantaloupe | Sow outdoors | Jun 21 – Jul 22 |
| Okra | Sow outdoors | Jun 14 – Jul 7 |
| Peas | Sow outdoors (spring) | Apr 21 – Jun 6 |
| Potatoes | Plant outdoors (spring) | Apr 21 – Jun 21 |
| Onions | Start seeds indoors (spring) | Mar 10 – Apr 6 |
| Onions | Transplant outdoors (spring) | May 8 – Jun 6 |
| Broccoli | Start seeds indoors (spring) | Apr 3 – May 7 |
| Broccoli | Transplant outdoors (spring) | May 8 – Jun 6 |
| Broccoli | Start seeds indoors (fall) | May 16 – May 26 |
| Broccoli | Transplant outdoors (fall) | Jun 15 – Jun 26 |
| Cabbage | Start seeds indoors (spring) | Mar 24 – Apr 21 |
| Cabbage | Transplant outdoors (spring) | Apr 21 – May 22 |
| Cabbage | Start seeds indoors (fall) | May 6 – Jun 5 |
| Cabbage | Transplant outdoors (fall) | Jun 5 – Jul 6 |
| Leaf lettuce | Sow outdoors (spring) | Apr 21 – Jul 7 |
| Leaf lettuce | Sow outdoors (fall) | Jun 5 – Jul 22 |
| Spinach | Sow outdoors (spring) | Apr 14 – May 28 |
| Spinach | Sow outdoors (fall) | Jun 22 – Jul 27 |
| Radishes | Sow outdoors (spring) | Apr 21 – Jun 11 |
| Radishes | Sow outdoors (fall) | Jun 5 – Aug 6 |
| Kale | Sow outdoors (spring) | May 8 – May 28 |
| Kale | Sow outdoors (fall) | May 29 – Jul 6 |
| Carrots | Sow outdoors (spring) | May 22 – Jul 7 |
| Carrots | Sow outdoors (fall) | May 6 – Jun 21 |
| Garlic | Plant outdoors (fall) | Sep 5 – Oct 6 |
Where these dates come from
ZIP code 59336 is matched to the NOAA station Mizpah 4 Nnw, MT, 15.5 km away, at 2,480 ft elevation (315 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Mizpah 4 Nnw, MT (used) | 2,480 ft | May 22 | Sep 15 |
| Terry, MT | 2,250 ft | May 12 | Sep 28 |
| Mildred 5 N, MT | 2,482 ft | May 20 | Sep 22 |
| Miles City F Wiley Fld, MT | 2,624 ft | May 8 | Sep 30 |
Frost dates near Ismay
- Mildred, MT 59341 · last May 20, first Sep 22
- Kinsey, MT 59338 · last May 8, first Sep 30
- Fallon, MT 59326 · last May 20, first Sep 22
- Terry, MT 59349 · last May 12, first Sep 28
- Miles City, MT 59301 · last May 8, first Sep 30
- Plevna, MT 59344 · last May 21, first Sep 20
- Willard, MT 59354 · last May 16, first Sep 26
- Baker, MT 59313 · last May 16, first Sep 26
Frequently asked questions
- When is the last frost in Ismay, MT?
- For ZIP code 59336, the average last spring frost (32°F) is May 22, based on NOAA 1991-2020 climate normals for the Mizpah 4 Nnw, MT weather station. There is a 1-in-10 chance of a frost after June 7.
- When is the first frost in Ismay, MT?
- The average first fall frost (32°F) is September 15. 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 59336?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 117 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.