Frost dates for 59230Glasgow, MT
The average last spring frost in Glasgow is May 6 and the average first fall frost is September 30, giving a typical growing season of about 145 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 6
- Average first fall frost
- Sep 30
- Growing season
- 145 days
Safer after May 18 (1-in-10 risk)
Possible by Sep 17 (1-in-10 risk)
Last frost typically in 191 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 5 · May 16 · May 30 | Sep 11 · Sep 23 · Oct 4 | 127 days | 100% |
| Frost / freeze (32°F) | Apr 24 · May 6 · May 18 | Sep 17 · Sep 30 · Oct 13 | 145 days | 100% |
| Hard freeze (28°F) | Apr 13 · Apr 26 · May 8 | Sep 24 · Oct 9 · Oct 24 | 164 days | 100% |
Planting calendar for Glasgow
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 5 – Jun 11 |
| Tomatoes | Transplant outdoors | May 22 – Jun 10 |
| Peppers | Start seeds indoors | Apr 5 – May 6 |
| Peppers | Transplant outdoors | Jun 5 – Jul 6 |
| Eggplant | Start seeds indoors | Apr 22 – May 21 |
| Eggplant | Transplant outdoors | Jun 5 – Jul 6 |
| Cucumbers | Sow outdoors | Jun 5 – Jun 20 |
| Summer squash | Sow outdoors | May 22 – Jul 6 |
| Winter squash & pumpkins | Sow outdoors | Jun 5 – Jul 6 |
| Snap beans | Sow outdoors | May 22 – Jul 13 |
| Sweet corn | Sow outdoors | May 22 – Jun 10 |
| Watermelon & cantaloupe | Sow outdoors | Jun 5 – Jul 6 |
| Okra | Sow outdoors | May 29 – Jun 21 |
| Peas | Sow outdoors (spring) | Apr 5 – May 21 |
| Potatoes | Plant outdoors (spring) | Apr 5 – Jun 5 |
| Onions | Start seeds indoors (spring) | Feb 22 – Mar 21 |
| Onions | Transplant outdoors (spring) | Apr 22 – May 21 |
| Broccoli | Start seeds indoors (spring) | Mar 18 – Apr 21 |
| Broccoli | Transplant outdoors (spring) | Apr 22 – May 21 |
| Broccoli | Start seeds indoors (fall) | May 31 – Jun 10 |
| Broccoli | Transplant outdoors (fall) | Jun 30 – Jul 11 |
| Cabbage | Start seeds indoors (spring) | Mar 8 – Apr 5 |
| Cabbage | Transplant outdoors (spring) | Apr 5 – May 6 |
| Cabbage | Start seeds indoors (fall) | May 21 – Jun 20 |
| Cabbage | Transplant outdoors (fall) | Jun 20 – Jul 21 |
| Leaf lettuce | Sow outdoors (spring) | Apr 5 – Jun 21 |
| Leaf lettuce | Sow outdoors (fall) | Jun 20 – Aug 6 |
| Spinach | Sow outdoors (spring) | Mar 29 – May 12 |
| Spinach | Sow outdoors (fall) | Jul 7 – Aug 11 |
| Radishes | Sow outdoors (spring) | Apr 5 – May 26 |
| Radishes | Sow outdoors (fall) | Jun 20 – Aug 21 |
| Kale | Sow outdoors (spring) | Apr 22 – May 12 |
| Kale | Sow outdoors (fall) | Jun 13 – Jul 21 |
| Carrots | Sow outdoors (spring) | May 6 – Jun 21 |
| Carrots | Sow outdoors (fall) | May 21 – Jul 6 |
| Garlic | Plant outdoors (fall) | Sep 20 – Oct 21 |
Where these dates come from
ZIP code 59230 is matched to the NOAA station Glasgow Intl Ap, MT, 1.5 km away, at 2,285 ft elevation (21 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Glasgow Intl Ap, MT (used) | 2,285 ft | May 6 | Sep 30 |
| Glasgow #2, MT | 2,090 ft | May 3 | Oct 1 |
| Nashua #2, MT | 2,067 ft | May 12 | Sep 24 |
| St Marie, MT | 2,756 ft | May 13 | Sep 27 |
Frost dates near Glasgow
- Nashua, MT 59248 · last May 12, first Sep 24
- Saint Marie, MT 59231 · last May 13, first Sep 27
- Fort Peck, MT 59223 · last May 8, first Oct 1
- Vandalia, MT 59273 · last May 3, first Oct 1
- Hinsdale, MT 59241 · last May 15, first Sep 23
- Frazer, MT 59225 · last May 13, first Sep 27
- Larslan, MT 59244 · last Jun 5, first Sep 2
- Richland, MT 59260 · last Jun 5, first Sep 2
Frequently asked questions
- When is the last frost in Glasgow, MT?
- For ZIP code 59230, the average last spring frost (32°F) is May 6, based on NOAA 1991-2020 climate normals for the Glasgow Intl Ap, MT weather station. There is a 1-in-10 chance of a frost after May 18.
- When is the first frost in Glasgow, MT?
- The average first fall frost (32°F) is September 30. There is a 1-in-10 chance of frost by September 17, so tender plants are at risk from that point on.
- How long is the growing season in 59230?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 145 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.