Frost dates for 59873Thompson Falls, MT
The average last spring frost in Thompson Falls is May 7 and the average first fall frost is October 4, giving a typical growing season of about 150 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 7
- Average first fall frost
- Oct 4
- Growing season
- 150 days
Safer after May 19 (1-in-10 risk)
Possible by Sep 21 (1-in-10 risk)
Last frost typically in 187 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 9 · May 22 · Jun 4 | Sep 7 · Sep 21 · Oct 3 | 122 days | 100% |
| Frost / freeze (32°F) | Apr 25 · May 7 · May 19 | Sep 21 · Oct 4 · Oct 19 | 150 days | 100% |
| Hard freeze (28°F) | Apr 5 · Apr 22 · May 6 | Oct 2 · Oct 18 · Nov 5 | 181 days | 100% |
Planting calendar for Thompson Falls
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 6 – Jun 12 |
| Tomatoes | Transplant outdoors | May 23 – Jun 14 |
| Peppers | Start seeds indoors | Apr 6 – May 7 |
| Peppers | Transplant outdoors | Jun 6 – Jul 7 |
| Eggplant | Start seeds indoors | Apr 23 – May 22 |
| Eggplant | Transplant outdoors | Jun 6 – Jul 7 |
| Cucumbers | Sow outdoors | Jun 6 – Jun 24 |
| Summer squash | Sow outdoors | May 23 – Jul 7 |
| Winter squash & pumpkins | Sow outdoors | Jun 6 – Jul 7 |
| Snap beans | Sow outdoors | May 23 – Jul 17 |
| Sweet corn | Sow outdoors | May 23 – Jun 14 |
| Watermelon & cantaloupe | Sow outdoors | Jun 6 – Jul 7 |
| Okra | Sow outdoors | May 30 – Jun 22 |
| Peas | Sow outdoors (spring) | Apr 6 – May 22 |
| Potatoes | Plant outdoors (spring) | Apr 6 – Jun 6 |
| Onions | Start seeds indoors (spring) | Feb 23 – Mar 22 |
| Onions | Transplant outdoors (spring) | Apr 23 – May 22 |
| Broccoli | Start seeds indoors (spring) | Mar 19 – Apr 22 |
| Broccoli | Transplant outdoors (spring) | Apr 23 – May 22 |
| Broccoli | Start seeds indoors (fall) | Jun 4 – Jun 14 |
| Broccoli | Transplant outdoors (fall) | Jul 4 – Jul 15 |
| Cabbage | Start seeds indoors (spring) | Mar 9 – Apr 6 |
| Cabbage | Transplant outdoors (spring) | Apr 6 – May 7 |
| Cabbage | Start seeds indoors (fall) | May 25 – Jun 24 |
| Cabbage | Transplant outdoors (fall) | Jun 24 – Jul 25 |
| Leaf lettuce | Sow outdoors (spring) | Apr 6 – Jun 22 |
| Leaf lettuce | Sow outdoors (fall) | Jun 24 – Aug 10 |
| Spinach | Sow outdoors (spring) | Mar 30 – May 13 |
| Spinach | Sow outdoors (fall) | Jul 11 – Aug 15 |
| Radishes | Sow outdoors (spring) | Apr 6 – May 27 |
| Radishes | Sow outdoors (fall) | Jun 24 – Aug 25 |
| Kale | Sow outdoors (spring) | Apr 23 – May 13 |
| Kale | Sow outdoors (fall) | Jun 17 – Jul 25 |
| Carrots | Sow outdoors (spring) | May 7 – Jun 22 |
| Carrots | Sow outdoors (fall) | May 25 – Jul 10 |
| Garlic | Plant outdoors (fall) | Sep 24 – Oct 25 |
Where these dates come from
ZIP code 59873 is matched to the NOAA station Thompson Falls Ph, MT, 0.9 km away, at 2,380 ft elevation (104 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Thompson Falls Ph, MT (used) | 2,380 ft | May 7 | Oct 4 |
| Haugan 1 W, MT | 3,160 ft | — | — |
| Mullan Pass Vor/Dme, ID | 6,028 ft | Jun 10 | Sep 23 |
| Trout Creek Rs, MT | 2,356 ft | May 20 | Sep 21 |
Frost dates near Thompson Falls
- De Borgia, MT 59830 · last —, first —
- Saltese, MT 59867 · last —, first —
- Haugan, MT 59842 · last —, first —
- Trout Creek, MT 59874 · last May 20, first Sep 21
- Saint Regis, MT 59866 · last —, first —
- Mullan, ID 83846 · last May 12, first Sep 30
- Murray, ID 83874 · last May 5, first Oct 2
- Plains, MT 59859 · last —, first —
Frequently asked questions
- When is the last frost in Thompson Falls, MT?
- For ZIP code 59873, the average last spring frost (32°F) is May 7, based on NOAA 1991-2020 climate normals for the Thompson Falls Ph, MT weather station. There is a 1-in-10 chance of a frost after May 19.
- When is the first frost in Thompson Falls, MT?
- The average first fall frost (32°F) is October 4. There is a 1-in-10 chance of frost by September 21, so tender plants are at risk from that point on.
- How long is the growing season in 59873?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 150 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.