Frost dates for 59522Chester, MT
The average last spring frost in Chester is May 24 and the average first fall frost is September 17, giving a typical growing season of about 115 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 24
- Average first fall frost
- Sep 17
- Growing season
- 115 days
Safer after Jun 9 (1-in-10 risk)
Possible by Sep 3 (1-in-10 risk)
Last frost typically in 209 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 24 · Jun 9 · Jul 1 | Aug 20 · Sep 5 · Sep 18 | 85 days | 100% |
| Frost / freeze (32°F) | May 11 · May 24 · Jun 9 | Sep 3 · Sep 17 · Sep 29 | 115 days | 100% |
| Hard freeze (28°F) | Apr 30 · May 11 · May 26 | Sep 14 · Sep 26 · Oct 8 | 137 days | 100% |
Planting calendar for Chester
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 23 – Jun 29 |
| Tomatoes | Transplant outdoors | Jun 9 – May 28 |
| Peppers | Start seeds indoors | Apr 23 – May 24 |
| Peppers | Transplant outdoors | Jun 23 – Jul 24 |
| Eggplant | Start seeds indoors | May 10 – Jun 8 |
| Eggplant | Transplant outdoors | Jun 23 – Jul 24 |
| Cucumbers | Sow outdoors | Jun 23 – Jun 7 |
| Summer squash | Sow outdoors | Jun 9 – Jul 24 |
| Winter squash & pumpkins | Sow outdoors | Jun 23 – Jul 24 |
| Snap beans | Sow outdoors | Jun 9 – Jun 30 |
| Sweet corn | Sow outdoors | Jun 9 – May 28 |
| Watermelon & cantaloupe | Sow outdoors | Jun 23 – Jul 24 |
| Okra | Sow outdoors | Jun 16 – Jul 9 |
| Peas | Sow outdoors (spring) | Apr 23 – Jun 8 |
| Potatoes | Plant outdoors (spring) | Apr 23 – Jun 23 |
| Onions | Start seeds indoors (spring) | Mar 12 – Apr 8 |
| Onions | Transplant outdoors (spring) | May 10 – Jun 8 |
| Broccoli | Start seeds indoors (spring) | Apr 5 – May 9 |
| Broccoli | Transplant outdoors (spring) | May 10 – Jun 8 |
| Broccoli | Start seeds indoors (fall) | May 18 – May 28 |
| Broccoli | Transplant outdoors (fall) | Jun 17 – Jun 28 |
| Cabbage | Start seeds indoors (spring) | Mar 26 – Apr 23 |
| Cabbage | Transplant outdoors (spring) | Apr 23 – May 24 |
| Cabbage | Start seeds indoors (fall) | May 8 – Jun 7 |
| Cabbage | Transplant outdoors (fall) | Jun 7 – Jul 8 |
| Leaf lettuce | Sow outdoors (spring) | Apr 23 – Jul 9 |
| Leaf lettuce | Sow outdoors (fall) | Jun 7 – Jul 24 |
| Spinach | Sow outdoors (spring) | Apr 16 – May 30 |
| Spinach | Sow outdoors (fall) | Jun 24 – Jul 29 |
| Radishes | Sow outdoors (spring) | Apr 23 – Jun 13 |
| Radishes | Sow outdoors (fall) | Jun 7 – Aug 8 |
| Kale | Sow outdoors (spring) | May 10 – May 30 |
| Kale | Sow outdoors (fall) | May 31 – Jul 8 |
| Carrots | Sow outdoors (spring) | May 24 – Jul 9 |
| Carrots | Sow outdoors (fall) | May 8 – Jun 23 |
| Garlic | Plant outdoors (fall) | Sep 7 – Oct 8 |
Where these dates come from
ZIP code 59522 is matched to the NOAA station Chester, MT, 6.2 km away, at 3,132 ft elevation (12 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Chester, MT (used) | 3,132 ft | May 24 | Sep 17 |
| Tiber Dam, MT | 2,850 ft | May 16 | Sep 23 |
| Joplin, MT | 3,323 ft | May 21 | Sep 19 |
| Rudyard 19S, MT | 2,878 ft | May 23 | Sep 19 |
Frost dates near Chester
- Lothair, MT 59461 · last May 24, first Sep 17
- Joplin, MT 59531 · last May 21, first Sep 19
- Inverness, MT 59530 · last May 21, first Sep 19
- Rudyard, MT 59540 · last May 21, first Sep 19
- Ledger, MT 59456 · last May 13, first Sep 29
- Hingham, MT 59528 · last May 24, first Sep 15
- Whitlash, MT 59545 · last —, first —
- Gildford, MT 59525 · last May 24, first Sep 15
Frequently asked questions
- When is the last frost in Chester, MT?
- For ZIP code 59522, the average last spring frost (32°F) is May 24, based on NOAA 1991-2020 climate normals for the Chester, MT weather station. There is a 1-in-10 chance of a frost after June 9.
- When is the first frost in Chester, MT?
- The average first fall frost (32°F) is September 17. 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 59522?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 115 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.