Frost dates in Helena, MT
The average last spring frost in Helena is around May 17 and the first fall frost is around September 21. That gives Helena an average growing season of about 127 days.
Last spring frost
| Early (10% chance after) | April 30 |
|---|---|
| Average (50%) | May 17 |
| Late (90%) | May 30 |
First fall frost
| Early (10%) | September 9 |
|---|---|
| Average (50%) | September 21 |
| Late (90% chance before) | October 10 |