Frost dates for 59215Circle, MT
The average last spring frost in Circle is May 17 and the average first fall frost is September 22, giving a typical growing season of about 126 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 17
- Average first fall frost
- Sep 22
- Growing season
- 126 days
Safer after May 31 (1-in-10 risk)
Possible by Sep 7 (1-in-10 risk)
Last frost typically in 202 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 15 · May 28 · Jun 15 | Aug 30 · Sep 13 · Sep 26 | 106 days | 100% |
| Frost / freeze (32°F) | May 4 · May 17 · May 31 | Sep 7 · Sep 22 · Oct 6 | 126 days | 100% |
| Hard freeze (28°F) | Apr 22 · May 6 · May 21 | Sep 17 · Oct 1 · Oct 17 | 146 days | 100% |
Planting calendar for Circle
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 16 – Jun 22 |
| Tomatoes | Transplant outdoors | Jun 2 – Jun 2 |
| Peppers | Start seeds indoors | Apr 16 – May 17 |
| Peppers | Transplant outdoors | Jun 16 – Jul 17 |
| Eggplant | Start seeds indoors | May 3 – Jun 1 |
| Eggplant | Transplant outdoors | Jun 16 – Jul 17 |
| Cucumbers | Sow outdoors | Jun 16 – Jun 12 |
| Summer squash | Sow outdoors | Jun 2 – Jul 17 |
| Winter squash & pumpkins | Sow outdoors | Jun 16 – Jul 17 |
| Snap beans | Sow outdoors | Jun 2 – Jul 5 |
| Sweet corn | Sow outdoors | Jun 2 – Jun 2 |
| Watermelon & cantaloupe | Sow outdoors | Jun 16 – Jul 17 |
| Okra | Sow outdoors | Jun 9 – Jul 2 |
| Peas | Sow outdoors (spring) | Apr 16 – Jun 1 |
| Potatoes | Plant outdoors (spring) | Apr 16 – Jun 16 |
| Onions | Start seeds indoors (spring) | Mar 5 – Apr 1 |
| Onions | Transplant outdoors (spring) | May 3 – Jun 1 |
| Broccoli | Start seeds indoors (spring) | Mar 29 – May 2 |
| Broccoli | Transplant outdoors (spring) | May 3 – Jun 1 |
| Broccoli | Start seeds indoors (fall) | May 23 – Jun 2 |
| Broccoli | Transplant outdoors (fall) | Jun 22 – Jul 3 |
| Cabbage | Start seeds indoors (spring) | Mar 19 – Apr 16 |
| Cabbage | Transplant outdoors (spring) | Apr 16 – May 17 |
| Cabbage | Start seeds indoors (fall) | May 13 – Jun 12 |
| Cabbage | Transplant outdoors (fall) | Jun 12 – Jul 13 |
| Leaf lettuce | Sow outdoors (spring) | Apr 16 – Jul 2 |
| Leaf lettuce | Sow outdoors (fall) | Jun 12 – Jul 29 |
| Spinach | Sow outdoors (spring) | Apr 9 – May 23 |
| Spinach | Sow outdoors (fall) | Jun 29 – Aug 3 |
| Radishes | Sow outdoors (spring) | Apr 16 – Jun 6 |
| Radishes | Sow outdoors (fall) | Jun 12 – Aug 13 |
| Kale | Sow outdoors (spring) | May 3 – May 23 |
| Kale | Sow outdoors (fall) | Jun 5 – Jul 13 |
| Carrots | Sow outdoors (spring) | May 17 – Jul 2 |
| Carrots | Sow outdoors (fall) | May 13 – Jun 28 |
| Garlic | Plant outdoors (fall) | Sep 12 – Oct 13 |
Where these dates come from
ZIP code 59215 is matched to the NOAA station Circle, MT, 2.1 km away, at 2,480 ft elevation (52 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Circle, MT (used) | 2,480 ft | May 17 | Sep 22 |
| Brockway 3 Wsw, MT | 2,630 ft | May 20 | Sep 19 |
| Terry 21 Nnw, MT | 3,142 ft | May 26 | Sep 17 |
| Vida 6 Ne, MT | 2,284 ft | May 16 | Sep 22 |
Frost dates near Circle
- Brockway, MT 59214 · last May 20, first Sep 19
- Lindsay, MT 59339 · last May 26, first Sep 17
- Vida, MT 59274 · last May 16, first Sep 22
- Bloomfield, MT 59315 · last May 17, first Sep 22
- Richey, MT 59259 · last May 16, first Sep 22
- Terry, MT 59349 · last May 12, first Sep 28
- Cohagen, MT 59322 · last May 25, first Sep 14
- Glendive, MT 59330 · last May 3, first Oct 4
Frequently asked questions
- When is the last frost in Circle, MT?
- For ZIP code 59215, the average last spring frost (32°F) is May 17, based on NOAA 1991-2020 climate normals for the Circle, MT weather station. There is a 1-in-10 chance of a frost after May 31.
- When is the first frost in Circle, MT?
- The average first fall frost (32°F) is September 22. 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 59215?
- 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.