Frost dates for 59058Mosby, MT
The average last spring frost in Mosby is May 5 and the average first fall frost is October 4, giving a typical growing season of about 151 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 5
- Average first fall frost
- Oct 4
- Growing season
- 151 days
Safer after May 26 (1-in-10 risk)
Possible by Sep 22 (1-in-10 risk)
Last frost typically in 190 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 4 · May 19 · Jun 4 | Sep 14 · Sep 26 · Oct 9 | 128 days | 100% |
| Frost / freeze (32°F) | Apr 20 · May 5 · May 26 | Sep 22 · Oct 4 · Oct 19 | 151 days | 100% |
| Hard freeze (28°F) | Apr 6 · Apr 20 · May 9 | Sep 30 · Oct 14 · Oct 29 | 173 days | 100% |
Planting calendar for Mosby
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 4 – Jun 10 |
| Tomatoes | Transplant outdoors | May 21 – Jun 14 |
| Peppers | Start seeds indoors | Apr 4 – May 5 |
| Peppers | Transplant outdoors | Jun 4 – Jul 5 |
| Eggplant | Start seeds indoors | Apr 21 – May 20 |
| Eggplant | Transplant outdoors | Jun 4 – Jul 5 |
| Cucumbers | Sow outdoors | Jun 4 – Jun 24 |
| Summer squash | Sow outdoors | May 21 – Jul 5 |
| Winter squash & pumpkins | Sow outdoors | Jun 4 – Jul 5 |
| Snap beans | Sow outdoors | May 21 – Jul 17 |
| Sweet corn | Sow outdoors | May 21 – Jun 14 |
| Watermelon & cantaloupe | Sow outdoors | Jun 4 – Jul 5 |
| Okra | Sow outdoors | May 28 – Jun 20 |
| Peas | Sow outdoors (spring) | Apr 4 – May 20 |
| Potatoes | Plant outdoors (spring) | Apr 4 – Jun 4 |
| Onions | Start seeds indoors (spring) | Feb 21 – Mar 20 |
| Onions | Transplant outdoors (spring) | Apr 21 – May 20 |
| Broccoli | Start seeds indoors (spring) | Mar 17 – Apr 20 |
| Broccoli | Transplant outdoors (spring) | Apr 21 – May 20 |
| Broccoli | Start seeds indoors (fall) | Jun 4 – Jun 14 |
| Broccoli | Transplant outdoors (fall) | Jul 4 – Jul 15 |
| Cabbage | Start seeds indoors (spring) | Mar 7 – Apr 4 |
| Cabbage | Transplant outdoors (spring) | Apr 4 – May 5 |
| Cabbage | Start seeds indoors (fall) | May 25 – Jun 24 |
| Cabbage | Transplant outdoors (fall) | Jun 24 – Jul 25 |
| Leaf lettuce | Sow outdoors (spring) | Apr 4 – Jun 20 |
| Leaf lettuce | Sow outdoors (fall) | Jun 24 – Aug 10 |
| Spinach | Sow outdoors (spring) | Mar 28 – May 11 |
| Spinach | Sow outdoors (fall) | Jul 11 – Aug 15 |
| Radishes | Sow outdoors (spring) | Apr 4 – May 25 |
| Radishes | Sow outdoors (fall) | Jun 24 – Aug 25 |
| Kale | Sow outdoors (spring) | Apr 21 – May 11 |
| Kale | Sow outdoors (fall) | Jun 17 – Jul 25 |
| Carrots | Sow outdoors (spring) | May 5 – Jun 20 |
| Carrots | Sow outdoors (fall) | May 25 – Jul 10 |
| Garlic | Plant outdoors (fall) | Sep 24 – Oct 25 |
Where these dates come from
ZIP code 59058 is matched to the NOAA station Mosby 4 Ene, MT, 13.7 km away, at 2,910 ft elevation (56 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Mosby 4 Ene, MT (used) | 2,910 ft | May 5 | Oct 4 |
| Melstone, MT | 2,932 ft | May 10 | Sep 29 |
| Flatwillow 4 Ene, MT | 3,292 ft | May 16 | Sep 28 |
| Ingomar 9 E, MT | 2,800 ft | May 21 | Sep 19 |
Frost dates near Mosby
- Sand Springs, MT 59077 · last May 5, first Oct 4
- Melstone, MT 59054 · last May 10, first Sep 29
- Sumatra, MT 59083 · last May 10, first Sep 29
- Winnett, MT 59087 · last May 16, first Sep 28
- Ingomar, MT 59039 · last May 21, first Sep 19
- Musselshell, MT 59059 · last May 10, first Sep 29
- Teigen, MT 59084 · last May 20, first Sep 24
- Brusett, MT 59318 · last May 18, first Sep 20
Frequently asked questions
- When is the last frost in Mosby, MT?
- For ZIP code 59058, the average last spring frost (32°F) is May 5, based on NOAA 1991-2020 climate normals for the Mosby 4 Ene, MT weather station. There is a 1-in-10 chance of a frost after May 26.
- When is the first frost in Mosby, MT?
- The average first fall frost (32°F) is October 4. There is a 1-in-10 chance of frost by September 22, so tender plants are at risk from that point on.
- How long is the growing season in 59058?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 151 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.