Frost dates in Keystone, IA
The average last spring frost in Keystone is around April 30 and the first fall frost is around October 5. That gives Keystone an average growing season of about 158 days.
Last spring frost
| Early (10% chance after) | April 17 |
|---|---|
| Average (50%) | April 30 |
| Late (90%) | May 17 |
First fall frost
| Early (10%) | September 21 |
|---|---|
| Average (50%) | October 5 |
| Late (90% chance before) | October 20 |