Frost dates for 59645White Sulphur Springs, MT
The average last spring frost in White Sulphur Springs is June 4 and the average first fall frost is September 11, giving a typical growing season of about 97 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Jun 4
- Average first fall frost
- Sep 11
- Growing season
- 97 days
Safer after Jun 20 (1-in-10 risk)
Possible by Aug 27 (1-in-10 risk)
Last frost typically in 215 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) | — | — | 65 days | 100% |
| Frost / freeze (32°F) | May 21 · Jun 4 · Jun 20 | Aug 27 · Sep 11 · Sep 27 | 97 days | 100% |
| Hard freeze (28°F) | May 5 · May 18 · Jun 1 | Sep 10 · Sep 25 · Oct 7 | 128 days | 100% |
Planting calendar for White Sulphur Springs
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 | May 4 – Jul 10 |
| Tomatoes | Transplant outdoors | Jun 20 – May 22 |
| Peppers | Start seeds indoors | May 4 – Jun 4 |
| Peppers | Transplant outdoors | Jul 4 – Aug 4 |
| Eggplant | Start seeds indoors | May 21 – Jun 19 |
| Eggplant | Transplant outdoors | Jul 4 – Aug 4 |
| Cucumbers | Sow outdoors | Jul 4 – Jun 1 |
| Summer squash | Sow outdoors | Jun 20 – Aug 4 |
| Winter squash & pumpkins | Sow outdoors | Jul 4 – Aug 4 |
| Snap beans | Sow outdoors | Jun 20 – Jun 24 |
| Sweet corn | Sow outdoors | Jun 20 – May 22 |
| Watermelon & cantaloupe | Sow outdoors | Jul 4 – Aug 4 |
| Okra | Sow outdoors | Jun 27 – Jul 20 |
| Peas | Sow outdoors (spring) | May 4 – Jun 19 |
| Potatoes | Plant outdoors (spring) | May 4 – Jul 4 |
| Onions | Start seeds indoors (spring) | Mar 23 – Apr 19 |
| Onions | Transplant outdoors (spring) | May 21 – Jun 19 |
| Broccoli | Start seeds indoors (spring) | Apr 16 – May 20 |
| Broccoli | Transplant outdoors (spring) | May 21 – Jun 19 |
| Broccoli | Start seeds indoors (fall) | May 12 – May 22 |
| Broccoli | Transplant outdoors (fall) | Jun 11 – Jun 22 |
| Cabbage | Start seeds indoors (spring) | Apr 6 – May 4 |
| Cabbage | Transplant outdoors (spring) | May 4 – Jun 4 |
| Cabbage | Start seeds indoors (fall) | May 2 – Jun 1 |
| Cabbage | Transplant outdoors (fall) | Jun 1 – Jul 2 |
| Leaf lettuce | Sow outdoors (spring) | May 4 – Jul 20 |
| Leaf lettuce | Sow outdoors (fall) | Jun 1 – Jul 18 |
| Spinach | Sow outdoors (spring) | Apr 27 – Jun 10 |
| Spinach | Sow outdoors (fall) | Jun 18 – Jul 23 |
| Radishes | Sow outdoors (spring) | May 4 – Jun 24 |
| Radishes | Sow outdoors (fall) | Jun 1 – Aug 2 |
| Kale | Sow outdoors (spring) | May 21 – Jun 10 |
| Kale | Sow outdoors (fall) | May 25 – Jul 2 |
| Carrots | Sow outdoors (spring) | Jun 4 – Jul 20 |
| Carrots | Sow outdoors (fall) | May 2 – Jun 17 |
| Garlic | Plant outdoors (fall) | Sep 1 – Oct 2 |
Where these dates come from
ZIP code 59645 is matched to the NOAA station White Sulphur Springs #2, MT, 15.2 km away, at 5,040 ft elevation (207 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| White Sulphur Springs #2, MT (used) | 5,040 ft | Jun 4 | Sep 11 |
| Millegan 14 Se, MT | 4,970 ft | Jun 11 | Sep 6 |
| Lennep 5 Sw, MT | 5,600 ft | — | — |
| Townsend 3Se, MT | 3,964 ft | May 19 | Sep 19 |
Frost dates near White Sulphur Springs
- Neihart, MT 59465 · last Jun 6, first Sep 12
- Ringling, MT 59642 · last —, first —
- Townsend, MT 59644 · last May 19, first Sep 19
- Winston, MT 59647 · last May 19, first Sep 19
- Monarch, MT 59463 · last Jun 6, first Sep 12
- Martinsdale, MT 59053 · last —, first —
- Radersburg, MT 59641 · last May 19, first Sep 19
- East Helena, MT 59635 · last May 9, first Sep 30
Frequently asked questions
- When is the last frost in White Sulphur Springs, MT?
- For ZIP code 59645, the average last spring frost (32°F) is June 4, based on NOAA 1991-2020 climate normals for the White Sulphur Springs #2, MT weather station. There is a 1-in-10 chance of a frost after June 20.
- When is the first frost in White Sulphur Springs, MT?
- The average first fall frost (32°F) is September 11. There is a 1-in-10 chance of frost by August 27, so tender plants are at risk from that point on.
- How long is the growing season in 59645?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 97 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.