Frost dates for 59829Darby, MT
The average last spring frost in Darby is May 24 and the average first fall frost is September 23, giving a typical growing season of about 118 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 24
- Average first fall frost
- Sep 23
- Growing season
- 118 days
Safer after Jun 14 (1-in-10 risk)
Possible by Sep 4 (1-in-10 risk)
Last frost typically in 204 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 28 · Jun 16 · Jul 4 | Aug 20 · Sep 6 · Sep 25 | 80 days | 100% |
| Frost / freeze (32°F) | May 6 · May 24 · Jun 14 | Sep 4 · Sep 23 · Oct 8 | 118 days | 100% |
| Hard freeze (28°F) | Apr 23 · May 5 · May 21 | Sep 18 · Oct 4 · Oct 19 | 150 days | 100% |
Planting calendar for Darby
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 23 – Jun 29 |
| Tomatoes | Transplant outdoors | Jun 9 – Jun 3 |
| Peppers | Start seeds indoors | Apr 23 – May 24 |
| Peppers | Transplant outdoors | Jun 23 – Jul 24 |
| Eggplant | Start seeds indoors | May 10 – Jun 8 |
| Eggplant | Transplant outdoors | Jun 23 – Jul 24 |
| Cucumbers | Sow outdoors | Jun 23 – Jun 13 |
| Summer squash | Sow outdoors | Jun 9 – Jul 24 |
| Winter squash & pumpkins | Sow outdoors | Jun 23 – Jul 24 |
| Snap beans | Sow outdoors | Jun 9 – Jul 6 |
| Sweet corn | Sow outdoors | Jun 9 – Jun 3 |
| Watermelon & cantaloupe | Sow outdoors | Jun 23 – Jul 24 |
| Okra | Sow outdoors | Jun 16 – Jul 9 |
| Peas | Sow outdoors (spring) | Apr 23 – Jun 8 |
| Potatoes | Plant outdoors (spring) | Apr 23 – Jun 23 |
| Onions | Start seeds indoors (spring) | Mar 12 – Apr 8 |
| Onions | Transplant outdoors (spring) | May 10 – Jun 8 |
| Broccoli | Start seeds indoors (spring) | Apr 5 – May 9 |
| Broccoli | Transplant outdoors (spring) | May 10 – Jun 8 |
| Broccoli | Start seeds indoors (fall) | May 24 – Jun 3 |
| Broccoli | Transplant outdoors (fall) | Jun 23 – Jul 4 |
| Cabbage | Start seeds indoors (spring) | Mar 26 – Apr 23 |
| Cabbage | Transplant outdoors (spring) | Apr 23 – May 24 |
| Cabbage | Start seeds indoors (fall) | May 14 – Jun 13 |
| Cabbage | Transplant outdoors (fall) | Jun 13 – Jul 14 |
| Leaf lettuce | Sow outdoors (spring) | Apr 23 – Jul 9 |
| Leaf lettuce | Sow outdoors (fall) | Jun 13 – Jul 30 |
| Spinach | Sow outdoors (spring) | Apr 16 – May 30 |
| Spinach | Sow outdoors (fall) | Jun 30 – Aug 4 |
| Radishes | Sow outdoors (spring) | Apr 23 – Jun 13 |
| Radishes | Sow outdoors (fall) | Jun 13 – Aug 14 |
| Kale | Sow outdoors (spring) | May 10 – May 30 |
| Kale | Sow outdoors (fall) | Jun 6 – Jul 14 |
| Carrots | Sow outdoors (spring) | May 24 – Jul 9 |
| Carrots | Sow outdoors (fall) | May 14 – Jun 29 |
| Garlic | Plant outdoors (fall) | Sep 13 – Oct 14 |
Where these dates come from
ZIP code 59829 is matched to the NOAA station Darby, MT, 1.4 km away, at 3,880 ft elevation (146 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Darby, MT (used) | 3,880 ft | May 24 | Sep 23 |
| Hamilton, MT | 3,585 ft | May 21 | Sep 22 |
| Sula 3 Ene, MT | 4,475 ft | — | — |
| Western Ag Rsch Ctr, MT | 3,608 ft | May 23 | Sep 21 |
Frost dates near Darby
- Conner, MT 59827 · last —, first —
- Grantsdale, MT 59835 · last May 21, first Sep 22
- Hamilton, MT 59840 · last May 21, first Sep 22
- Sula, MT 59871 · last —, first —
- Corvallis, MT 59828 · last May 23, first Sep 21
- Pinesdale, MT 59841 · last May 23, first Sep 21
- Victor, MT 59875 · last May 23, first Sep 21
- Gibbonsville, ID 83463 · last —, first —
Frequently asked questions
- When is the last frost in Darby, MT?
- For ZIP code 59829, the average last spring frost (32°F) is May 24, based on NOAA 1991-2020 climate normals for the Darby, MT weather station. There is a 1-in-10 chance of a frost after June 14.
- When is the first frost in Darby, MT?
- The average first fall frost (32°F) is September 23. There is a 1-in-10 chance of frost by September 4, so tender plants are at risk from that point on.
- How long is the growing season in 59829?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 118 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.