Frost dates in Montana

Across Montana, the typical last spring frost is around May 20 and the first fall frost around Sep 22. Your own dates depend on where you are in the state; find your county below.

Most of the state's last spring frosts fall between May 9 and Jun 6, and its first fall frosts between Sep 8 and Oct 1.

These are the dates with a 50% chance of a 32°F frost on or after (spring) or on or before (fall), so plan tender crops a week or two after the spring date and keep row cover handy. For dates at your exact ZIP code, use the zone and frost date lookup; for what to plant when, see the planting guide by frost date.

Hardiness zones in Montana: zone 3b, zone 4a, zone 4b, zone 5a, zone 5b, zone 6a, zone 6b

Frost dates by county in Montana

CountyLast spring frostFirst fall frostGrowing season
BeaverheadJun 10Sep 13About 95 days
Big HornMay 14Sep 24About 133 days
BlaineMay 16Sep 23About 130 days
BroadwaterMay 19Sep 19About 123 days
CarbonMay 29Sep 15About 109 days
CarterMay 20Sep 23About 126 days
CascadeJun 2Sep 12About 102 days
ChouteauMay 17Sep 23About 129 days
CusterMay 13Sep 30About 140 days
DanielsMay 28Sep 6About 101 days
DawsonMay 16Sep 25About 132 days
Deer LodgeJun 1Sep 14About 105 days
FallonMay 16Sep 26About 133 days
FergusMay 19Sep 23About 127 days
FlatheadMay 16Sep 25About 132 days
GallatinMay 26Sep 22About 119 days
GarfieldMay 18Sep 25About 130 days
GlacierJun 3Sep 8About 97 days
Golden ValleyMay 22Sep 23About 124 days
GraniteJun 1Sep 19About 110 days
HillMay 21Sep 19About 121 days
JeffersonJun 13Sep 8About 87 days
Judith BasinMay 28Sep 21About 116 days
LakeMay 12Oct 5About 146 days
Lewis and ClarkMay 21Sep 15About 117 days
LibertyMay 24Sep 17About 116 days
LincolnMay 14Sep 25About 134 days
MadisonJun 8Sep 14About 98 days
McConeMay 17Sep 22About 128 days
MeagherJun 4Sep 8About 96 days
MineralJun 10Sep 23About 105 days
MissoulaMay 10Oct 1About 144 days
MusselshellMay 20Sep 29About 132 days
ParkMay 27Sep 14About 110 days
PetroleumMay 18Sep 21About 126 days
PhillipsMay 19Sep 23About 127 days
PonderaMay 20Sep 19About 122 days
Powder RiverMay 16Sep 28About 135 days
PowellJun 9Sep 8About 91 days
PrairieMay 20Sep 28About 131 days
RavalliMay 23Sep 21About 121 days
RichlandMay 11Sep 27About 139 days
RooseveltMay 21Sep 20About 122 days
RosebudMay 10Sep 29About 142 days
SandersMay 17Sep 23About 129 days
SheridanMay 19Sep 18About 122 days
Silver BowJun 13Sep 5About 84 days
StillwaterMay 29Sep 14About 108 days
Sweet GrassJun 1Sep 26About 117 days
TetonMay 20Sep 27About 130 days
TooleMay 17Sep 25About 131 days
TreasureMay 10Sep 29About 142 days
ValleyMay 15Sep 26About 134 days
WheatlandJun 1Sep 16About 107 days
WibauxMay 27Sep 16About 112 days
YellowstoneMay 12Oct 1About 142 days

Source: NOAA NCEI U.S. Climate Normals 1991–2020, 50% probability of 32°F, from the weather station nearest each ZIP code; each county shows the middle value across its ZIP codes. Hills, valleys and cities can run a week or more earlier or later.

Frost dates for other states