Frost dates for 59917Eureka, MT
The average last spring frost in Eureka is May 11 and the average first fall frost is September 27, giving a typical growing season of about 138 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 11
- Average first fall frost
- Sep 27
- Growing season
- 138 days
Safer after May 25 (1-in-10 risk)
Possible by Sep 10 (1-in-10 risk)
Last frost typically in 196 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 12 · May 26 · Jun 8 | Aug 28 · Sep 13 · Sep 30 | 109 days | 100% |
| Frost / freeze (32°F) | Apr 28 · May 11 · May 25 | Sep 10 · Sep 27 · Oct 9 | 138 days | 100% |
| Hard freeze (28°F) | Apr 10 · Apr 28 · May 12 | Sep 26 · Oct 7 · Oct 26 | 164 days | 100% |
Planting calendar for Eureka
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 10 – Jun 16 |
| Tomatoes | Transplant outdoors | May 27 – Jun 7 |
| Peppers | Start seeds indoors | Apr 10 – May 11 |
| Peppers | Transplant outdoors | Jun 10 – Jul 11 |
| Eggplant | Start seeds indoors | Apr 27 – May 26 |
| Eggplant | Transplant outdoors | Jun 10 – Jul 11 |
| Cucumbers | Sow outdoors | Jun 10 – Jun 17 |
| Summer squash | Sow outdoors | May 27 – Jul 11 |
| Winter squash & pumpkins | Sow outdoors | Jun 10 – Jul 11 |
| Snap beans | Sow outdoors | May 27 – Jul 10 |
| Sweet corn | Sow outdoors | May 27 – Jun 7 |
| Watermelon & cantaloupe | Sow outdoors | Jun 10 – Jul 11 |
| Okra | Sow outdoors | Jun 3 – Jun 26 |
| Peas | Sow outdoors (spring) | Apr 10 – May 26 |
| Potatoes | Plant outdoors (spring) | Apr 10 – Jun 10 |
| Onions | Start seeds indoors (spring) | Feb 27 – Mar 26 |
| Onions | Transplant outdoors (spring) | Apr 27 – May 26 |
| Broccoli | Start seeds indoors (spring) | Mar 23 – Apr 26 |
| Broccoli | Transplant outdoors (spring) | Apr 27 – May 26 |
| Broccoli | Start seeds indoors (fall) | May 28 – Jun 7 |
| Broccoli | Transplant outdoors (fall) | Jun 27 – Jul 8 |
| Cabbage | Start seeds indoors (spring) | Mar 13 – Apr 10 |
| Cabbage | Transplant outdoors (spring) | Apr 10 – May 11 |
| Cabbage | Start seeds indoors (fall) | May 18 – Jun 17 |
| Cabbage | Transplant outdoors (fall) | Jun 17 – Jul 18 |
| Leaf lettuce | Sow outdoors (spring) | Apr 10 – Jun 26 |
| Leaf lettuce | Sow outdoors (fall) | Jun 17 – Aug 3 |
| Spinach | Sow outdoors (spring) | Apr 3 – May 17 |
| Spinach | Sow outdoors (fall) | Jul 4 – Aug 8 |
| Radishes | Sow outdoors (spring) | Apr 10 – May 31 |
| Radishes | Sow outdoors (fall) | Jun 17 – Aug 18 |
| Kale | Sow outdoors (spring) | Apr 27 – May 17 |
| Kale | Sow outdoors (fall) | Jun 10 – Jul 18 |
| Carrots | Sow outdoors (spring) | May 11 – Jun 26 |
| Carrots | Sow outdoors (fall) | May 18 – Jul 3 |
| Garlic | Plant outdoors (fall) | Sep 17 – Oct 18 |
Where these dates come from
ZIP code 59917 is matched to the NOAA station Eureka Rs, MT, 7.5 km away, at 2,532 ft elevation (224 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Eureka Rs, MT (used) | 2,532 ft | May 11 | Sep 27 |
| Fortine 1 N, MT | 3,000 ft | May 16 | Sep 18 |
| Olney, MT | 3,165 ft | — | — |
| Yaak 9Nne, MT | 3,085 ft | — | — |
Frost dates near Eureka
- Fortine, MT 59918 · last May 16, first Sep 18
- Rexford, MT 59930 · last May 11, first Sep 27
- Trego, MT 59934 · last May 16, first Sep 18
- Stryker, MT 59933 · last —, first —
- Olney, MT 59927 · last —, first —
- Polebridge, MT 59928 · last —, first —
- Libby, MT 59923 · last May 23, first Sep 21
- Whitefish, MT 59937 · last May 16, first Sep 25
Frequently asked questions
- When is the last frost in Eureka, MT?
- For ZIP code 59917, the average last spring frost (32°F) is May 11, based on NOAA 1991-2020 climate normals for the Eureka Rs, MT weather station. There is a 1-in-10 chance of a frost after May 25.
- When is the first frost in Eureka, MT?
- The average first fall frost (32°F) is September 27. There is a 1-in-10 chance of frost by September 10, so tender plants are at risk from that point on.
- How long is the growing season in 59917?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 138 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.