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Frost Dates for Helena, MT
Use our 2023 Frost Dates Calculator to find the average dates of the last light freeze of spring and first light freeze of fall for locations across the U.S. and Canada. Simply enter your ZIP or Postal code in the field above to see frost dates for your location (based on the nearest weather station), as well as the length of your growing season based on frost dates.
|Nearest Climate Station||Altitude||Last Spring Frost||First Fall Frost||Growing Season|
|HELENA RGNL AP, MT||3828'||May 15||Sep 25||132 days|
Last and first frost dates are 30% probability. Calculated using 1991-2020 Climate Normals from NOAA.
What are 2023 Frost Dates?
A frost date is the average date of the last light freeze in spring or the first light freeze in fall.
The classification of freeze temperatures is based on their effect on plants:
- Light freeze: 29° to 32°F (-1.7° to 0°C)—tender plants are killed.
- Moderate freeze: 25° to 28°F (-3.9° to -2.2°C)—widely destructive to most vegetation.
- Severe freeze: 24°F (-4.4°C) and colder—heavy damage to most garden plants.
Note that frost dates are only an estimate based on historical climate data and are not set in stone. The probability of a frost occurring after the spring frost date or before the fall frost date is 30%, which means that there is still a chance of frost occurring before or after the given dates!
Frost is predicted when air temperatures reach 32°F (0°C), but because it is colder closer to the ground, a frost may occur even when air temperatures are just above freezing. Always keep an eye on your local weather forecast and plan to protect tender plants accordingly. Weather, topography, and microclimates may also cause considerable variations in the occurrence of frost in your garden. Learn how to protect plants from frost.
Frost dates are calculated based on data from the NOAA National Centers for Environmental Information.
Wondering when to plant what? Get a head start on gardening with our Planting Calendar, customized to your location!