Keystone, SD frost dates
Last spring frostMay 15median date
First fall frostOct 1median date
Growing season139 daysfrost-free
Hardiness zone5aZone 5a
How Keystone compares
- In 8 years out of 10, the last spring frost in Keystone falls between May 1 and May 29, a 28-day window. The first fall frost falls between September 16 and October 19.
- The median last frost is 9 days later than the South Dakota median of May 6.
- Its 139-day growing season is longer than 10% of the 363 South Dakota places with a regular frost season (state median 149 days).
- The last frost is 12 days later than the zone 5a median of May 3. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 5a chart.
- The weather station records an average of 152 nights a year at or below 32°F.
- Compared with Rapid City, SD, 23 km away, the last frost here is 12 days later than there and the growing season is 19 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | May 1 |
| 50% (median) | May 15 |
| 10% (safe for tender plants) | May 29 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 16 |
| 50% (median) | October 1 |
| 90% (late) | October 19 |
Frost here means 32°F (0°C). A median date means half of years have their last frost earlier and half later.
Planting calendar for Keystone, SD
Keystone, SD frost dates — last frost May 15, first frost Oct 1, zone 5a. whenisthelastfrost.com
Crop
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Start indoors: Feb 20 to Mar 6Transplant outside: Apr 17 to May 1
Start indoors: Mar 6 to Mar 20Transplant outside: May 29 to Jun 12
Start indoors: Mar 6 to Mar 20Transplant outside: May 29 to Jun 12
Start indoors: Mar 20 to Apr 3Transplant outside: May 22 to Jun 5
Start indoors: Mar 20 to Apr 3Transplant outside: Apr 24 to May 8Sow outdoors: Apr 17 to May 22Plant for fall: Aug 6 to Sep 3
Start indoors: Mar 20 to Apr 3Transplant outside: Apr 17 to May 1Sow outdoors: Apr 17 to May 1Plant for fall: Jul 23 to Aug 13
Start indoors: Mar 20 to Apr 3Transplant outside: May 1 to May 15Plant for fall: Jun 25 to Jul 16
Start indoors: Mar 20 to Apr 3Transplant outside: Apr 24 to May 8Plant for fall: Jun 25 to Jul 16
Start indoors: Mar 20 to Apr 3Transplant outside: May 1 to May 15Plant for fall: Jun 25 to Jul 16
Start indoors: Apr 3 to Apr 17Transplant outside: Jun 5 to Jun 19Sow outdoors: Jun 5 to Jun 19
Start indoors: Apr 3 to Apr 17Transplant outside: May 22 to Jun 5
Sow outdoors: Apr 3 to Apr 24Plant for fall: Jul 9 to Jul 30
Sow outdoors: Apr 3 to Apr 24Plant for fall: Aug 6 to Aug 27
Sow outdoors: Apr 10 to May 22Plant for fall: Aug 20 to Sep 10
Start indoors: Apr 17 to Apr 24Transplant outside: May 29 to Jun 5Sow outdoors: May 22 to Jun 5Plant for fall: Jul 16 to Jul 30
Start indoors: Apr 17 to Apr 24Sow outdoors: May 22 to Jun 5Plant for fall: Jul 23 to Aug 6
Start indoors: Apr 17 to Apr 24Sow outdoors: May 22 to Jun 5
Start indoors: Apr 17 to Apr 24Transplant outside: May 29 to Jun 12
Sow outdoors: Apr 24 to May 22Plant for fall: Jul 9 to Jul 23
Sow outdoors: Apr 24 to May 22Plant for fall: Jul 23 to Aug 6
Sow outdoors: Apr 24 to May 15
Sow outdoors: May 1 to May 29Plant for fall: Jul 23 to Aug 6
Sow outdoors: May 1 to May 22Plant for fall: Aug 6 to Aug 27
Sow outdoors: May 22 to Jun 12Plant for fall: Jul 16 to Jul 30
Sow outdoors: May 22 to Jun 5
Transplant outside: May 29 to Jun 19
Plant for fall: Sep 17 to Oct 22
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Keystone, SD
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 20 – Mar 6 | Apr 17 – May 1 | — | — |
| Peppers | Mar 6 – Mar 20 | May 29 – Jun 12 | — | — |
| Eggplant | Mar 6 – Mar 20 | May 29 – Jun 12 | — | — |
| Tomatoes | Mar 20 – Apr 3 | May 22 – Jun 5 | — | — |
| Lettuce | Mar 20 – Apr 3 | Apr 24 – May 8 | Apr 17 – May 22 | Aug 6 – Sep 3 |
| Kale | Mar 20 – Apr 3 | Apr 17 – May 1 | Apr 17 – May 1 | Jul 23 – Aug 13 |
| Broccoli | Mar 20 – Apr 3 | May 1 – May 15 | — | Jun 25 – Jul 16 |
| Cabbage | Mar 20 – Apr 3 | Apr 24 – May 8 | — | Jun 25 – Jul 16 |
| Cauliflower | Mar 20 – Apr 3 | May 1 – May 15 | — | Jun 25 – Jul 16 |
| Okra | Apr 3 – Apr 17 | Jun 5 – Jun 19 | Jun 5 – Jun 19 | — |
| Basil | Apr 3 – Apr 17 | May 22 – Jun 5 | — | — |
| Peas | — | — | Apr 3 – Apr 24 | Jul 9 – Jul 30 |
| Spinach | — | — | Apr 3 – Apr 24 | Aug 6 – Aug 27 |
| Radishes | — | — | Apr 10 – May 22 | Aug 20 – Sep 10 |
| Cucumbers | Apr 17 – Apr 24 | May 29 – Jun 5 | May 22 – Jun 5 | Jul 16 – Jul 30 |
| Zucchini & Summer Squash | Apr 17 – Apr 24 | — | May 22 – Jun 5 | Jul 23 – Aug 6 |
| Winter Squash & Pumpkins | Apr 17 – Apr 24 | — | May 22 – Jun 5 | — |
| Melons & Watermelon | Apr 17 – Apr 24 | May 29 – Jun 12 | — | — |
| Carrots | — | — | Apr 24 – May 22 | Jul 9 – Jul 23 |
| Beets | — | — | Apr 24 – May 22 | Jul 23 – Aug 6 |
| Potatoes | — | — | Apr 24 – May 15 | — |
| Swiss Chard | — | — | May 1 – May 29 | Jul 23 – Aug 6 |
| Cilantro | — | — | May 1 – May 22 | Aug 6 – Aug 27 |
| Green Beans | — | — | May 22 – Jun 12 | Jul 16 – Jul 30 |
| Sweet Corn | — | — | May 22 – Jun 5 | — |
| Sweet Potatoes | — | May 29 – Jun 19 | — | — |
| Garlic | — | — | — | Sep 17 – Oct 22 |
Dates come from the median frost dates and common extension-service timing. Adjust for your soil temperature, microclimate and the varieties you grow.
About these dates
Based on 1991–2020 NOAA climate normals for the Mt Rushmore Nmem, SD weather station, 5 km away (elevation 5,312 ft (1,619 m)).
Frost dates near Keystone
- Hill City Jun 1 · Sep 10
- Hermosa May 15 · Oct 1
- Rapid City May 3 · Oct 8
- Custer May 15 · Sep 29
- Fairburn May 15 · Sep 29
- Black Hawk May 10 · Oct 5
- Pringle May 15 · Sep 29
- Box Elder May 12 · Oct 1
- Nemo May 20 · Sep 25
- Piedmont May 10 · Oct 5
Frequently asked questions
When is the last frost in Keystone, SD?
The median last spring frost in Keystone, SD is May 15. There is still about a 10% chance of frost after May 29, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Keystone, SD?
The median first fall frost is October 1, with about a 10% chance of frost before September 16.
How long is the growing season in Keystone, SD?
About 139 days between the median last spring frost and first fall frost.
What planting zone is Keystone, SD?
Keystone, SD is in USDA hardiness zone 5a.