Frost dates for 59419Bynum, MT
The average last spring frost in Bynum is May 28 and the average first fall frost is September 12, giving a typical growing season of about 104 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 28
- Average first fall frost
- Sep 12
- Growing season
- 104 days
Safer after Jun 20 (1-in-10 risk)
Possible by Aug 30 (1-in-10 risk)
Last frost typically in 206 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) | — | — | 69 days | 100% |
| Frost / freeze (32°F) | May 15 · May 28 · Jun 20 | Aug 30 · Sep 12 · Sep 27 | 104 days | 100% |
| Hard freeze (28°F) | May 1 · May 14 · May 27 | Sep 9 · Sep 25 · Oct 7 | 134 days | 100% |
Planting calendar for Bynum
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 27 – Jul 3 |
| Tomatoes | Transplant outdoors | Jun 13 – May 23 |
| Peppers | Start seeds indoors | Apr 27 – May 28 |
| Peppers | Transplant outdoors | Jun 27 – Jul 28 |
| Eggplant | Start seeds indoors | May 14 – Jun 12 |
| Eggplant | Transplant outdoors | Jun 27 – Jul 28 |
| Cucumbers | Sow outdoors | Jun 27 – Jun 2 |
| Summer squash | Sow outdoors | Jun 13 – Jul 28 |
| Winter squash & pumpkins | Sow outdoors | Jun 27 – Jul 28 |
| Snap beans | Sow outdoors | Jun 13 – Jun 25 |
| Sweet corn | Sow outdoors | Jun 13 – May 23 |
| Watermelon & cantaloupe | Sow outdoors | Jun 27 – Jul 28 |
| Okra | Sow outdoors | Jun 20 – Jul 13 |
| Peas | Sow outdoors (spring) | Apr 27 – Jun 12 |
| Potatoes | Plant outdoors (spring) | Apr 27 – Jun 27 |
| Onions | Start seeds indoors (spring) | Mar 16 – Apr 12 |
| Onions | Transplant outdoors (spring) | May 14 – Jun 12 |
| Broccoli | Start seeds indoors (spring) | Apr 9 – May 13 |
| Broccoli | Transplant outdoors (spring) | May 14 – Jun 12 |
| Broccoli | Start seeds indoors (fall) | May 13 – May 23 |
| Broccoli | Transplant outdoors (fall) | Jun 12 – Jun 23 |
| Cabbage | Start seeds indoors (spring) | Mar 30 – Apr 27 |
| Cabbage | Transplant outdoors (spring) | Apr 27 – May 28 |
| Cabbage | Start seeds indoors (fall) | May 3 – Jun 2 |
| Cabbage | Transplant outdoors (fall) | Jun 2 – Jul 3 |
| Leaf lettuce | Sow outdoors (spring) | Apr 27 – Jul 13 |
| Leaf lettuce | Sow outdoors (fall) | Jun 2 – Jul 19 |
| Spinach | Sow outdoors (spring) | Apr 20 – Jun 3 |
| Spinach | Sow outdoors (fall) | Jun 19 – Jul 24 |
| Radishes | Sow outdoors (spring) | Apr 27 – Jun 17 |
| Radishes | Sow outdoors (fall) | Jun 2 – Aug 3 |
| Kale | Sow outdoors (spring) | May 14 – Jun 3 |
| Kale | Sow outdoors (fall) | May 26 – Jul 3 |
| Carrots | Sow outdoors (spring) | May 28 – Jul 13 |
| Carrots | Sow outdoors (fall) | May 3 – Jun 18 |
| Garlic | Plant outdoors (fall) | Sep 2 – Oct 3 |
Where these dates come from
ZIP code 59419 is matched to the NOAA station Choteau, MT, 19.8 km away, at 3,845 ft elevation (82 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Choteau, MT (used) | 3,845 ft | May 28 | Sep 12 |
| Bynum 4 Sse, MT | 4,039 ft | May 16 | Sep 27 |
| Blackleaf, MT | 4,235 ft | Jun 9 | Sep 3 |
| Choteau 8Ne, MT | 3,741 ft | May 20 | Sep 22 |
Frost dates near Bynum
- Pendroy, MT 59467 · last Jun 9, first Sep 3
- Choteau, MT 59422 · last May 28, first Sep 12
- Dupuyer, MT 59432 · last Jun 9, first Sep 3
- Valier, MT 59486 · last May 17, first Sep 24
- Conrad, MT 59425 · last May 20, first Sep 19
- Brady, MT 59416 · last May 20, first Sep 19
- Dutton, MT 59433 · last May 20, first Sep 19
- Fairfield, MT 59436 · last May 13, first Sep 27
Frequently asked questions
- When is the last frost in Bynum, MT?
- For ZIP code 59419, the average last spring frost (32°F) is May 28, based on NOAA 1991-2020 climate normals for the Choteau, MT weather station. There is a 1-in-10 chance of a frost after June 20.
- When is the first frost in Bynum, MT?
- The average first fall frost (32°F) is September 12. There is a 1-in-10 chance of frost by August 30, so tender plants are at risk from that point on.
- How long is the growing season in 59419?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 104 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.