Frost dates for 59923Libby, MT
The average last spring frost in Libby is May 23 and the average first fall frost is September 21, giving a typical growing season of about 120 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 23
- Average first fall frost
- Sep 21
- Growing season
- 120 days
Safer after Jun 7 (1-in-10 risk)
Possible by Sep 3 (1-in-10 risk)
Last frost typically in 208 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) | — | — | 85 days | 100% |
| Frost / freeze (32°F) | May 9 · May 23 · Jun 7 | Sep 3 · Sep 21 · Oct 8 | 120 days | 100% |
| Hard freeze (28°F) | Apr 23 · May 7 · May 20 | Sep 20 · Oct 5 · Oct 29 | 152 days | 100% |
Planting calendar for Libby
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 22 – Jun 28 |
| Tomatoes | Transplant outdoors | Jun 8 – Jun 1 |
| Peppers | Start seeds indoors | Apr 22 – May 23 |
| Peppers | Transplant outdoors | Jun 22 – Jul 23 |
| Eggplant | Start seeds indoors | May 9 – Jun 7 |
| Eggplant | Transplant outdoors | Jun 22 – Jul 23 |
| Cucumbers | Sow outdoors | Jun 22 – Jun 11 |
| Summer squash | Sow outdoors | Jun 8 – Jul 23 |
| Winter squash & pumpkins | Sow outdoors | Jun 22 – Jul 23 |
| Snap beans | Sow outdoors | Jun 8 – Jul 4 |
| Sweet corn | Sow outdoors | Jun 8 – Jun 1 |
| Watermelon & cantaloupe | Sow outdoors | Jun 22 – Jul 23 |
| Okra | Sow outdoors | Jun 15 – Jul 8 |
| Peas | Sow outdoors (spring) | Apr 22 – Jun 7 |
| Potatoes | Plant outdoors (spring) | Apr 22 – Jun 22 |
| Onions | Start seeds indoors (spring) | Mar 11 – Apr 7 |
| Onions | Transplant outdoors (spring) | May 9 – Jun 7 |
| Broccoli | Start seeds indoors (spring) | Apr 4 – May 8 |
| Broccoli | Transplant outdoors (spring) | May 9 – Jun 7 |
| Broccoli | Start seeds indoors (fall) | May 22 – Jun 1 |
| Broccoli | Transplant outdoors (fall) | Jun 21 – Jul 2 |
| Cabbage | Start seeds indoors (spring) | Mar 25 – Apr 22 |
| Cabbage | Transplant outdoors (spring) | Apr 22 – May 23 |
| Cabbage | Start seeds indoors (fall) | May 12 – Jun 11 |
| Cabbage | Transplant outdoors (fall) | Jun 11 – Jul 12 |
| Leaf lettuce | Sow outdoors (spring) | Apr 22 – Jul 8 |
| Leaf lettuce | Sow outdoors (fall) | Jun 11 – Jul 28 |
| Spinach | Sow outdoors (spring) | Apr 15 – May 29 |
| Spinach | Sow outdoors (fall) | Jun 28 – Aug 2 |
| Radishes | Sow outdoors (spring) | Apr 22 – Jun 12 |
| Radishes | Sow outdoors (fall) | Jun 11 – Aug 12 |
| Kale | Sow outdoors (spring) | May 9 – May 29 |
| Kale | Sow outdoors (fall) | Jun 4 – Jul 12 |
| Carrots | Sow outdoors (spring) | May 23 – Jul 8 |
| Carrots | Sow outdoors (fall) | May 12 – Jun 27 |
| Garlic | Plant outdoors (fall) | Sep 11 – Oct 12 |
Where these dates come from
ZIP code 59923 is matched to the NOAA station Libby 1 Ne Rs, MT, 2.9 km away, at 2,096 ft elevation (10 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Libby 1 Ne Rs, MT (used) | 2,096 ft | May 23 | Sep 21 |
| Libby, MT | 2,140 ft | May 10 | Sep 26 |
| Libby Dam (Base), MT | 2,110 ft | May 11 | Oct 1 |
| Troy, MT | 1,929 ft | May 14 | Sep 25 |
Frost dates near Libby
- Troy, MT 59935 · last May 14, first Sep 25
- Noxon, MT 59853 · last —, first —
- Heron, MT 59844 · last May 20, first Sep 20
- Clark Fork, ID 83811 · last May 9, first Oct 8
- Hope, ID 83836 · last May 8, first Sep 28
- Trego, MT 59934 · last May 16, first Sep 18
- Moyie Springs, ID 83845 · last Apr 30, first Oct 4
- Naples, ID 83847 · last Apr 30, first Oct 4
Frequently asked questions
- When is the last frost in Libby, MT?
- For ZIP code 59923, the average last spring frost (32°F) is May 23, based on NOAA 1991-2020 climate normals for the Libby 1 Ne Rs, MT weather station. There is a 1-in-10 chance of a frost after June 7.
- When is the first frost in Libby, MT?
- The average first fall frost (32°F) is September 21. There is a 1-in-10 chance of frost by September 3, so tender plants are at risk from that point on.
- How long is the growing season in 59923?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 120 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.