Last frost date in Great Falls, MT
Expect the last frost in Great Falls around May 6. Frost after May 19 happens in only one year out of ten. The first fall frost usually arrives about October 1, which leaves 147 frost-free days. An early freeze before September 17 happens one year in ten.
- Safe after (10% risk)
- May 19
- Average first frost
- Oct 1
- Frost-free season
- 147 days
- Hard freeze (28°F) ends
- Apr 24
Hard freeze likely Fri night, low 26°F
National Weather Service forecast, updated Oct 22, 12:57 UTC
- ThuOct 2244°
- FriOct 2326°hard freeze
- SatOct 2427°hard freeze
- SunOct 2528°hard freeze
- MonOct 2629°frost
- TueOct 2730°frost
- WedOct 2828°hard freeze
Planting calendar for Great Falls
Windows count forward or back from the average frost dates above. Click a crop for dates across Montana.
TomatoesMay 13–May 27
PumpkinsMay 20–Jun 3
SunflowersMay 6–May 27
CucumbersMay 20–May 27
CornMay 13–May 27
Sweet potatoesMay 27–Jun 10
WatermelonMay 20–Jun 3
Green beansMay 13–Jun 3
ZucchiniMay 13–May 27
OkraMay 27–Jun 10
PeppersMay 20–Jun 3
BasilMay 13–May 27
Butternut squashMay 13–May 27
CantaloupeMay 20–Jun 3
EggplantMay 20–Jun 3
PotatoesApr 8–Apr 22
OnionsMar 25–Apr 15
CarrotsApr 15–May 20
LettuceApr 22–May 13
BroccoliApr 8–Apr 22
BeetsApr 8–May 20
PeasMar 25–Apr 8
CabbageApr 8–Apr 22
RadishesApr 1–May 13
Brussels sproutsApr 22–May 6
SpinachMar 25–Apr 15
CilantroApr 22–May 13
KaleApr 8–Apr 22
Collard greensApr 8–Apr 22
TurnipsApr 8–Apr 22
DillMay 6–May 20
CeleryMay 13–May 20
CauliflowerApr 22–May 6
LeeksApr 22–May 6
Swiss chardApr 22–May 20
ParsleyApr 22–May 13
Tulip bulbsSep 17–Oct 22
GarlicSep 10–Oct 15
Daffodil bulbsSep 3–Oct 15
StrawberriesApr 8–Apr 22
AsparagusApr 8–Apr 22Frost probabilities
| Threshold | Spring, 90% chance later | Spring, 50% | Spring, 10% | Fall, 10% chance earlier | Fall, 50% | Fall, 90% |
|---|---|---|---|---|---|---|
| Light frost, 32°F | Apr 23 | May 6 | May 19 | Sep 17 | Oct 1 | Oct 16 |
| Hard freeze, 28°F | Apr 7 | Apr 24 | May 8 | Sep 25 | Oct 11 | Oct 29 |
Read the spring 10% column as the date after which only one year in ten still gets frost. That is the safer date for tomatoes, peppers and basil.
Where these numbers come from
NOAA station Great Falls 16st (USC00243749) sits 1.4 miles from the center of Great Falls at 3,505 feet. Its averages cover 1991 to 2020. Low spots, valleys and open fields can keep getting frost a week or two after the station stops; city centers and lakeshores usually get less of it.
Questions
When is the last frost in Great Falls, MT?
The average last frost date in Great Falls is May 6, based on NOAA 1991–2020 climate normals. There is a 10% chance of frost after May 19.
When is the first frost in Great Falls?
The first frost in fall usually comes around October 1. One year in ten it arrives before September 17.
How long is the growing season in Great Falls?
About 147 days between the average last and first frost.
When should I plant tomatoes in Great Falls?
Plant tomato seedlings outside from May 13 to May 27. Start seeds indoors six to eight weeks earlier.