White Harbor Labs › Frost Dates › States › Montana
Frost Dates in Montana
First and last frost dates across Montana, computed from 158 NOAA weather stations (1991–2020 climate normals). Your exact date depends on your city and microclimate — use the ZIP lookup on the main tool for a station-specific answer.
Last spring frost
May 20
statewide median · range Apr 30–Jun 16
First fall frost
Sep 21
statewide median · range Sep 2–Oct 15
Growing season
123 days
median · range 78–165
Stations used
158
NOAA 1991–2020 normals
Frost dates by city
Median dates from the nearest NOAA station to each city. The "cautious" date is the 10% spring value — planting after it means only a ~10% chance of a later frost.
| City | Nearest station | Last spring frost | First fall frost | Growing season | Safe transplant |
|---|---|---|---|---|---|
| Billings | Billings Wtp · 1 mi | May 10 (cautious: May 24) | Oct 1 | 142 days | May 24 |
| Missoula | Missoula Intl Ap · 6 mi | May 16 (cautious: Jun 1) | Sep 26 | 130 days | May 30 |
| Bozeman | Bozeman Montana State Univ · 1 mi | May 26 (cautious: Jun 14) | Sep 22 | 116 days | Jun 9 |
How frost varies across Montana
Spring frost timing spans about 47 days across the state. Norris Madison Pwr House in Montana typically sees its last spring frost around April 30, while Ennis in Montana doesn't clear frost until about June 16. Within any city, low spots and valleys run colder than the station average; areas near buildings and pavement run warmer.
When to plant in Montana
As a rule of thumb, cool-season crops (lettuce, peas, spinach) can go in 2–4 weeks before your last spring frost; warm-season transplants (tomatoes, peppers) should wait about 2 weeks after it — around June 3 for the statewide median. Check your city's row above rather than the statewide median: a 47-day statewide spread makes the city-level date the one that matters.
These are climate normals (what's typical), not forecasts. For the current year, watch the 10-day forecast around your planting date.
How this is computed
Statewide medians are the median of the 158 NOAA stations' median frost dates — half the stations run earlier, half later. City rows use the nearest station with 30-year freeze records. Dates are 32°F freeze probabilities from NOAA NCEI 1991–2020 U.S. Climate Normals; nothing is estimated or interpolated.
More states
Frequently asked questions
When is the last frost date in Montana?
The statewide median last spring frost is May 20, but it ranges from April 30 to June 16 depending on where in the state you are. Use your city's row in the table above, or the ZIP lookup on the main tool, for a station-specific date.
When can I plant tomatoes outside in Montana?
Warm-season transplants like tomatoes should wait about two weeks after your last spring frost — around June 3 for the statewide median. Your city may differ by weeks; check the "safe transplant" column in the city table.
How long is the growing season in Montana?
The median growing season across 158 NOAA stations is 123 days, ranging from 78 to 165 days by location.
Why do frost dates vary so much within Montana?
Frost timing follows latitude, elevation, and local terrain. Across Montana, last spring frost dates span about 47 days — from around April 30 near Norris Madison Pwr House to June 16 near Ennis. Microclimates (low spots, valleys, urban heat) shift dates further at the garden level.
Where does this data come from?
All frost dates are computed from the NOAA National Centers for Environmental Information 1991–2020 U.S. Climate Normals freeze data (public domain), using each station's 32°F freeze probability statistics. No dates are estimated or interpolated.