Frost dates for 82440Ralston, WY
The average last spring frost in Ralston is May 15 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 15
- Average first fall frost
- Sep 25
- Growing season
- 132 days
Safer after Jun 1 (1-in-10 risk)
Possible by Sep 11 (1-in-10 risk)
Last frost typically in 193 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 14 · May 31 · Jun 17 | Sep 2 · Sep 16 · Sep 29 | 106 days | 100% |
| Frost / freeze (32°F) | May 1 · May 15 · Jun 1 | Sep 11 · Sep 25 · Oct 10 | 132 days | 100% |
| Hard freeze (28°F) | Apr 19 · May 2 · May 19 | Sep 21 · Oct 6 · Oct 21 | 156 days | 100% |
Planting calendar for Ralston
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 14 – Jun 20 |
| Tomatoes | Transplant outdoors | May 31 – Jun 5 |
| Peppers | Start seeds indoors | Apr 14 – May 15 |
| Peppers | Transplant outdoors | Jun 14 – Jul 15 |
| Eggplant | Start seeds indoors | May 1 – May 30 |
| Eggplant | Transplant outdoors | Jun 14 – Jul 15 |
| Cucumbers | Sow outdoors | Jun 14 – Jun 15 |
| Summer squash | Sow outdoors | May 31 – Jul 15 |
| Winter squash & pumpkins | Sow outdoors | Jun 14 – Jul 15 |
| Snap beans | Sow outdoors | May 31 – Jul 8 |
| Sweet corn | Sow outdoors | May 31 – Jun 5 |
| Watermelon & cantaloupe | Sow outdoors | Jun 14 – Jul 15 |
| Okra | Sow outdoors | Jun 7 – Jun 30 |
| Peas | Sow outdoors (spring) | Apr 14 – May 30 |
| Potatoes | Plant outdoors (spring) | Apr 14 – Jun 14 |
| Onions | Start seeds indoors (spring) | Mar 3 – Mar 30 |
| Onions | Transplant outdoors (spring) | May 1 – May 30 |
| Broccoli | Start seeds indoors (spring) | Mar 27 – Apr 30 |
| Broccoli | Transplant outdoors (spring) | May 1 – May 30 |
| Broccoli | Start seeds indoors (fall) | May 26 – Jun 5 |
| Broccoli | Transplant outdoors (fall) | Jun 25 – Jul 6 |
| Cabbage | Start seeds indoors (spring) | Mar 17 – Apr 14 |
| Cabbage | Transplant outdoors (spring) | Apr 14 – May 15 |
| Cabbage | Start seeds indoors (fall) | May 16 – Jun 15 |
| Cabbage | Transplant outdoors (fall) | Jun 15 – Jul 16 |
| Leaf lettuce | Sow outdoors (spring) | Apr 14 – Jun 30 |
| Leaf lettuce | Sow outdoors (fall) | Jun 15 – Aug 1 |
| Spinach | Sow outdoors (spring) | Apr 7 – May 21 |
| Spinach | Sow outdoors (fall) | Jul 2 – Aug 6 |
| Radishes | Sow outdoors (spring) | Apr 14 – Jun 4 |
| Radishes | Sow outdoors (fall) | Jun 15 – Aug 16 |
| Kale | Sow outdoors (spring) | May 1 – May 21 |
| Kale | Sow outdoors (fall) | Jun 8 – Jul 16 |
| Carrots | Sow outdoors (spring) | May 15 – Jun 30 |
| Carrots | Sow outdoors (fall) | May 16 – Jul 1 |
| Garlic | Plant outdoors (fall) | Sep 15 – Oct 16 |
Where these dates come from
ZIP code 82440 is matched to the NOAA station Heart Mtn, WY, 7.3 km away, at 4,790 ft elevation (230 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Heart Mtn, WY (used) | 4,790 ft | May 15 | Sep 25 |
| Powell Fld Stn, WY | 4,372 ft | May 19 | Sep 20 |
| Deaver, WY | 4,105 ft | May 6 | Oct 1 |
| Cody, WY | 5,280 ft | May 12 | Oct 1 |
Frost dates near Ralston
- Powell, WY 82435 · last May 19, first Sep 20
- Byron, WY 82412 · last May 6, first Oct 1
- Cody, WY 82414 · last May 17, first Oct 3
- Deaver, WY 82421 · last May 6, first Oct 1
- Frannie, WY 82423 · last May 6, first Oct 1
- Cowley, WY 82420 · last May 9, first Sep 29
- Lovell, WY 82431 · last May 9, first Sep 29
- Belfry, MT 59008 · last May 18, first Sep 22
Frequently asked questions
- When is the last frost in Ralston, WY?
- For ZIP code 82440, the average last spring frost (32°F) is May 15, based on NOAA 1991-2020 climate normals for the Heart Mtn, WY weather station. There is a 1-in-10 chance of a frost after June 1.
- When is the first frost in Ralston, WY?
- The average first fall frost (32°F) is September 25. There is a 1-in-10 chance of frost by September 11, so tender plants are at risk from that point on.
- How long is the growing season in 82440?
- 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.