Frost dates for 57751Keystone, SD
The average last spring frost in Keystone is May 28 and the average first fall frost is September 18, giving a typical growing season of about 112 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 28
- Average first fall frost
- Sep 18
- Growing season
- 112 days
Safer after Jun 11 (1-in-10 risk)
Possible by Sep 4 (1-in-10 risk)
Last frost typically in 207 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 28 · Jun 13 · Jul 4 | Aug 24 · Sep 7 · Sep 20 | 85 days | 100% |
| Frost / freeze (32°F) | May 16 · May 28 · Jun 11 | Sep 4 · Sep 18 · Oct 1 | 112 days | 100% |
| Hard freeze (28°F) | May 4 · May 15 · May 28 | Sep 14 · Sep 29 · Oct 12 | 136 days | 100% |
Planting calendar for Keystone
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 27 – Jul 3 |
| Tomatoes | Transplant outdoors | Jun 13 – May 29 |
| Peppers | Start seeds indoors | Apr 27 – May 28 |
| Peppers | Transplant outdoors | Jun 27 – Jul 28 |
| Eggplant | Start seeds indoors | May 14 – Jun 12 |
| Eggplant | Transplant outdoors | Jun 27 – Jul 28 |
| Cucumbers | Sow outdoors | Jun 27 – Jun 8 |
| Summer squash | Sow outdoors | Jun 13 – Jul 28 |
| Winter squash & pumpkins | Sow outdoors | Jun 27 – Jul 28 |
| Snap beans | Sow outdoors | Jun 13 – Jul 1 |
| Sweet corn | Sow outdoors | Jun 13 – May 29 |
| Watermelon & cantaloupe | Sow outdoors | Jun 27 – Jul 28 |
| Okra | Sow outdoors | Jun 20 – Jul 13 |
| Peas | Sow outdoors (spring) | Apr 27 – Jun 12 |
| Potatoes | Plant outdoors (spring) | Apr 27 – Jun 27 |
| Onions | Start seeds indoors (spring) | Mar 16 – Apr 12 |
| Onions | Transplant outdoors (spring) | May 14 – Jun 12 |
| Broccoli | Start seeds indoors (spring) | Apr 9 – May 13 |
| Broccoli | Transplant outdoors (spring) | May 14 – Jun 12 |
| Broccoli | Start seeds indoors (fall) | May 19 – May 29 |
| Broccoli | Transplant outdoors (fall) | Jun 18 – Jun 29 |
| Cabbage | Start seeds indoors (spring) | Mar 30 – Apr 27 |
| Cabbage | Transplant outdoors (spring) | Apr 27 – May 28 |
| Cabbage | Start seeds indoors (fall) | May 9 – Jun 8 |
| Cabbage | Transplant outdoors (fall) | Jun 8 – Jul 9 |
| Leaf lettuce | Sow outdoors (spring) | Apr 27 – Jul 13 |
| Leaf lettuce | Sow outdoors (fall) | Jun 8 – Jul 25 |
| Spinach | Sow outdoors (spring) | Apr 20 – Jun 3 |
| Spinach | Sow outdoors (fall) | Jun 25 – Jul 30 |
| Radishes | Sow outdoors (spring) | Apr 27 – Jun 17 |
| Radishes | Sow outdoors (fall) | Jun 8 – Aug 9 |
| Kale | Sow outdoors (spring) | May 14 – Jun 3 |
| Kale | Sow outdoors (fall) | Jun 1 – Jul 9 |
| Carrots | Sow outdoors (spring) | May 28 – Jul 13 |
| Carrots | Sow outdoors (fall) | May 9 – Jun 24 |
| Garlic | Plant outdoors (fall) | Sep 8 – Oct 9 |
Where these dates come from
ZIP code 57751 is matched to the NOAA station Pactola Dam, SD, 20.8 km away, at 4,720 ft elevation (31 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Pactola Dam, SD (used) | 4,720 ft | May 28 | Sep 18 |
| Mt Rushmore Nmem, SD | 5,311 ft | May 15 | Oct 1 |
| Hill City, SD | 4,946 ft | Jun 1 | Sep 10 |
| Custer, SD | 5,480 ft | May 18 | Sep 28 |
Frost dates near Keystone
- Rapid City, SD 57702 · last May 20, first Sep 25
- Hill City, SD 57745 · last Jun 1, first Sep 10
- Hermosa, SD 57744 · last May 3, first Oct 8
- Custer, SD 57730 · last May 15, first Sep 29
- Fairburn, SD 57738 · last May 16, first Sep 27
- Black Hawk, SD 57718 · last May 20, first Sep 25
- Pringle, SD 57773 · last Jun 1, first Sep 10
- Box Elder, SD 57719 · last May 12, first Oct 1
Frequently asked questions
- When is the last frost in Keystone, SD?
- For ZIP code 57751, the average last spring frost (32°F) is May 28, based on NOAA 1991-2020 climate normals for the Pactola Dam, SD weather station. There is a 1-in-10 chance of a frost after June 11.
- When is the first frost in Keystone, SD?
- The average first fall frost (32°F) is September 18. There is a 1-in-10 chance of frost by September 4, so tender plants are at risk from that point on.
- How long is the growing season in 57751?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 112 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.