Frost dates in Keystone, SD
The average last spring frost in Keystone is around May 15 and the first fall frost is around September 29. That gives Keystone an average growing season of about 137 days.
Last spring frost
| Early (10% chance after) | April 29 |
|---|---|
| Average (50%) | May 15 |
| Late (90%) | June 4 |
First fall frost
| Early (10%) | September 12 |
|---|---|
| Average (50%) | September 29 |
| Late (90% chance before) | October 13 |