Frost dates for 59935Troy, MT
The average last spring frost in Troy is May 14 and the average first fall frost is September 25, giving a typical growing season of about 132 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 14
- Average first fall frost
- Sep 25
- Growing season
- 132 days
Safer after May 31 (1-in-10 risk)
Possible by Sep 9 (1-in-10 risk)
Last frost typically in 199 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 18 · Jun 2 · Jun 27 | Aug 24 · Sep 7 · Sep 24 | 96 days | 100% |
| Frost / freeze (32°F) | Apr 29 · May 14 · May 31 | Sep 9 · Sep 25 · Oct 9 | 132 days | 100% |
| Hard freeze (28°F) | Apr 14 · Apr 29 · May 14 | Sep 21 · Oct 6 · Oct 30 | 162 days | 100% |
Planting calendar for Troy
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 13 – Jun 19 |
| Tomatoes | Transplant outdoors | May 30 – Jun 5 |
| Peppers | Start seeds indoors | Apr 13 – May 14 |
| Peppers | Transplant outdoors | Jun 13 – Jul 14 |
| Eggplant | Start seeds indoors | Apr 30 – May 29 |
| Eggplant | Transplant outdoors | Jun 13 – Jul 14 |
| Cucumbers | Sow outdoors | Jun 13 – Jun 15 |
| Summer squash | Sow outdoors | May 30 – Jul 14 |
| Winter squash & pumpkins | Sow outdoors | Jun 13 – Jul 14 |
| Snap beans | Sow outdoors | May 30 – Jul 8 |
| Sweet corn | Sow outdoors | May 30 – Jun 5 |
| Watermelon & cantaloupe | Sow outdoors | Jun 13 – Jul 14 |
| Okra | Sow outdoors | Jun 6 – Jun 29 |
| Peas | Sow outdoors (spring) | Apr 13 – May 29 |
| Potatoes | Plant outdoors (spring) | Apr 13 – Jun 13 |
| Onions | Start seeds indoors (spring) | Mar 2 – Mar 29 |
| Onions | Transplant outdoors (spring) | Apr 30 – May 29 |
| Broccoli | Start seeds indoors (spring) | Mar 26 – Apr 29 |
| Broccoli | Transplant outdoors (spring) | Apr 30 – May 29 |
| Broccoli | Start seeds indoors (fall) | May 26 – Jun 5 |
| Broccoli | Transplant outdoors (fall) | Jun 25 – Jul 6 |
| Cabbage | Start seeds indoors (spring) | Mar 16 – Apr 13 |
| Cabbage | Transplant outdoors (spring) | Apr 13 – May 14 |
| Cabbage | Start seeds indoors (fall) | May 16 – Jun 15 |
| Cabbage | Transplant outdoors (fall) | Jun 15 – Jul 16 |
| Leaf lettuce | Sow outdoors (spring) | Apr 13 – Jun 29 |
| Leaf lettuce | Sow outdoors (fall) | Jun 15 – Aug 1 |
| Spinach | Sow outdoors (spring) | Apr 6 – May 20 |
| Spinach | Sow outdoors (fall) | Jul 2 – Aug 6 |
| Radishes | Sow outdoors (spring) | Apr 13 – Jun 3 |
| Radishes | Sow outdoors (fall) | Jun 15 – Aug 16 |
| Kale | Sow outdoors (spring) | Apr 30 – May 20 |
| Kale | Sow outdoors (fall) | Jun 8 – Jul 16 |
| Carrots | Sow outdoors (spring) | May 14 – Jun 29 |
| Carrots | Sow outdoors (fall) | May 16 – Jul 1 |
| Garlic | Plant outdoors (fall) | Sep 15 – Oct 16 |
Where these dates come from
ZIP code 59935 is matched to the NOAA station Troy, MT, 1.8 km away, at 1,929 ft elevation (610 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Troy, MT (used) | 1,929 ft | May 14 | Sep 25 |
| Libby, MT | 2,140 ft | May 10 | Sep 26 |
| Libby 1 Ne Rs, MT | 2,096 ft | May 23 | Sep 21 |
| Bonners Ferry, ID | 2,075 ft | Apr 30 | Oct 4 |
Frost dates near Troy
- Libby, MT 59923 · last May 23, first Sep 21
- Naples, ID 83847 · last Apr 30, first Oct 4
- Moyie Springs, ID 83845 · last Apr 30, first Oct 4
- Hope, ID 83836 · last May 8, first Sep 28
- Clark Fork, ID 83811 · last May 9, first Oct 8
- Bonners Ferry, ID 83805 · last Apr 30, first Oct 4
- Noxon, MT 59853 · last —, first —
- Heron, MT 59844 · last May 20, first Sep 20
Frequently asked questions
- When is the last frost in Troy, MT?
- For ZIP code 59935, the average last spring frost (32°F) is May 14, based on NOAA 1991-2020 climate normals for the Troy, MT weather station. There is a 1-in-10 chance of a frost after May 31.
- When is the first frost in Troy, MT?
- The average first fall frost (32°F) is September 25. There is a 1-in-10 chance of frost by September 9, so tender plants are at risk from that point on.
- How long is the growing season in 59935?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 132 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.