Frost dates in Idaho

Across Idaho, the typical last spring frost is around May 15 and the first fall frost around Sep 28. 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 Apr 24 and Jun 12, and its first fall frosts between Sep 9 and Oct 17.

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 Idaho: zone 4a, zone 4b, zone 5a, zone 5b, zone 6a, zone 6b, zone 7a, zone 7b

Frost dates by county in Idaho

CountyLast spring frostFirst fall frostGrowing season
AdaApr 24Oct 21About 180 days
AdamsMay 10Oct 2About 145 days
BannockMay 21Sep 24About 126 days
Bear LakeJun 17Sep 3About 78 days
BenewahMay 11Oct 4About 146 days
BinghamMay 21Sep 20About 122 days
BlaineMay 13Oct 2About 142 days
BoiseJun 1Sep 10About 101 days
BonnerMay 12Sep 22About 133 days
BonnevilleJun 9Sep 11About 94 days
BoundaryMay 4Oct 4About 153 days
ButteMay 24Sep 22About 121 days
CamasJun 16Sep 14About 90 days
CanyonApr 29Oct 13About 167 days
CaribouMay 29Sep 17About 111 days
CassiaMay 15Oct 2About 140 days
ClarkJun 5Sep 30About 117 days
ClearwaterMay 16Sep 23About 130 days
CusterMay 21Sep 18About 120 days
ElmoreMay 2Oct 3About 154 days
FranklinMay 16Sep 28About 135 days
FremontMay 21Sep 21About 123 days
GemMay 31Oct 17About 139 days
GoodingMay 2Oct 14About 165 days
IdahoMay 6Oct 9About 156 days
JeffersonJun 3Sep 11About 100 days
JeromeMay 7Oct 5About 151 days
KootenaiApr 22Oct 18About 179 days
LatahMay 15Sep 23About 131 days
LemhiJun 1Sep 17About 108 days
LewisMay 24Sep 25About 124 days
LincolnApr 24Oct 16About 175 days
MadisonMay 29Sep 13About 107 days
MinidokaMay 7Oct 4About 150 days
Nez PerceMay 23Oct 20About 150 days
OneidaMay 22Sep 20About 121 days
OwyheeMay 1Oct 6About 158 days
PayetteApr 22Oct 13About 174 days
PowerMay 20Sep 26About 129 days
ShoshoneMay 14Sep 26About 135 days
TetonJun 15Sep 9About 86 days
Twin FallsMay 9Oct 4About 148 days
ValleyJun 12Sep 19About 99 days
WashingtonApr 23Oct 13About 173 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