Frost dates for 59820Alberton, MT
The average last spring frost in Alberton is May 18 and the average first fall frost is September 25, giving a typical growing season of about 126 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 18
- Average first fall frost
- Sep 25
- Growing season
- 126 days
Safer after Jun 6 (1-in-10 risk)
Possible by Sep 7 (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 23 · Jun 11 · Jul 2 | Aug 28 · Sep 9 · Sep 26 | 92 days | 100% |
| Frost / freeze (32°F) | May 5 · May 18 · Jun 6 | Sep 7 · Sep 25 · Oct 6 | 126 days | 100% |
| Hard freeze (28°F) | Apr 20 · May 3 · May 15 | Sep 23 · Oct 5 · Oct 21 | 153 days | 100% |
Planting calendar for Alberton
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 17 – Jun 23 |
| Tomatoes | Transplant outdoors | Jun 3 – Jun 5 |
| Peppers | Start seeds indoors | Apr 17 – May 18 |
| Peppers | Transplant outdoors | Jun 17 – Jul 18 |
| Eggplant | Start seeds indoors | May 4 – Jun 2 |
| Eggplant | Transplant outdoors | Jun 17 – Jul 18 |
| Cucumbers | Sow outdoors | Jun 17 – Jun 15 |
| Summer squash | Sow outdoors | Jun 3 – Jul 18 |
| Winter squash & pumpkins | Sow outdoors | Jun 17 – Jul 18 |
| Snap beans | Sow outdoors | Jun 3 – Jul 8 |
| Sweet corn | Sow outdoors | Jun 3 – Jun 5 |
| Watermelon & cantaloupe | Sow outdoors | Jun 17 – Jul 18 |
| Okra | Sow outdoors | Jun 10 – Jul 3 |
| Peas | Sow outdoors (spring) | Apr 17 – Jun 2 |
| Potatoes | Plant outdoors (spring) | Apr 17 – Jun 17 |
| Onions | Start seeds indoors (spring) | Mar 6 – Apr 2 |
| Onions | Transplant outdoors (spring) | May 4 – Jun 2 |
| Broccoli | Start seeds indoors (spring) | Mar 30 – May 3 |
| Broccoli | Transplant outdoors (spring) | May 4 – Jun 2 |
| Broccoli | Start seeds indoors (fall) | May 26 – Jun 5 |
| Broccoli | Transplant outdoors (fall) | Jun 25 – Jul 6 |
| Cabbage | Start seeds indoors (spring) | Mar 20 – Apr 17 |
| Cabbage | Transplant outdoors (spring) | Apr 17 – May 18 |
| Cabbage | Start seeds indoors (fall) | May 16 – Jun 15 |
| Cabbage | Transplant outdoors (fall) | Jun 15 – Jul 16 |
| Leaf lettuce | Sow outdoors (spring) | Apr 17 – Jul 3 |
| Leaf lettuce | Sow outdoors (fall) | Jun 15 – Aug 1 |
| Spinach | Sow outdoors (spring) | Apr 10 – May 24 |
| Spinach | Sow outdoors (fall) | Jul 2 – Aug 6 |
| Radishes | Sow outdoors (spring) | Apr 17 – Jun 7 |
| Radishes | Sow outdoors (fall) | Jun 15 – Aug 16 |
| Kale | Sow outdoors (spring) | May 4 – May 24 |
| Kale | Sow outdoors (fall) | Jun 8 – Jul 16 |
| Carrots | Sow outdoors (spring) | May 18 – Jul 3 |
| Carrots | Sow outdoors (fall) | May 16 – Jul 1 |
| Garlic | Plant outdoors (fall) | Sep 15 – Oct 16 |
Where these dates come from
ZIP code 59820 is matched to the NOAA station Alberton, MT, 2.8 km away, at 3,060 ft elevation (2,458 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Alberton, MT (used) | 3,060 ft | May 18 | Sep 25 |
| Missoula Intl Ap, MT | 3,192 ft | May 16 | Sep 26 |
| Missoula 6 Nw Wfo, MT | 3,197 ft | May 6 | Oct 4 |
| Superior, MT | 2,710 ft | May 17 | Sep 23 |
Frost dates near Alberton
- Huson, MT 59846 · last May 18, first Sep 25
- Frenchtown, MT 59834 · last May 10, first Oct 1
- Missoula, MT 59804 · last May 10, first Oct 1
- Superior, MT 59872 · last May 17, first Sep 23
- Lolo, MT 59847 · last May 16, first Sep 26
- Arlee, MT 59821 · last May 12, first Oct 2
- Dixon, MT 59831 · last May 12, first Oct 2
- Ravalli, MT 59863 · last May 12, first Oct 2
Frequently asked questions
- When is the last frost in Alberton, MT?
- For ZIP code 59820, the average last spring frost (32°F) is May 18, based on NOAA 1991-2020 climate normals for the Alberton, MT weather station. There is a 1-in-10 chance of a frost after June 6.
- When is the first frost in Alberton, MT?
- The average first fall frost (32°F) is September 25. There is a 1-in-10 chance of frost by September 7, so tender plants are at risk from that point on.
- How long is the growing season in 59820?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 126 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.