Just to the due west of the Continental Divide in the northern Rocky Mountains , Idaho is a land of great deal and intermountain valleys and washstand . The state endures a continental mood with short , comfortably warm summertime but jolting winters with frigid temperatures and snow . Elevation affects temperatures : in general the cities and counties of Idaho that are in the south ’s lower elevations around the Snake River enjoy a slimly milder climate than the rest of the land . The planting zones in Idaho are relevant only for year - one shot plants , not for seasonal plants only crop in the summertime growing time of year .
USDA Winter Hardiness Zones
The United States Department of Agriculture ( USDA ) winter hardiness zone creates areas that share common average wintertime lower limit temperature . In Idaho ’s tremendous elevation sport , using the USDA zone can be difficult , misleading and frustrating , since winter minimum temperatures will change with only a twain hundred feet in elevation or exposure to winds , etc . The USDA map for Idaho ( see references link ) is unmanageable to show , but overall comprehend zones 2 through 7 . That correlate to winter depressed temperatures ranging from 0 to -45 degrees F. Use the USDA zona finder from the National Gardening Association to observe your zone based on your nothing code .
Idaho’s Climate Zones
The " Sunset Western Garden Book " creates mood zone ground on many more factors that plainly temperatures ( like the USDA ) . The Sunset clime zones take into account Idaho ’s latitude , lift , seasonal rain regimes , humidness , influence of ocean and continental air masse , and soil types . The bulk of central Idaho is in mood zone 1A , among the coldest of climates and options for garden . In the southern region around the broad Snake River Valley , and in the extreme northwest along the border with Washington , the climate zona is either 2A , 2B , 3A or 3B. The large the number , the milder the climate , with A being harsher or cold-blooded than B. Here is a flying reference chart of city and Sunset clime zone identification :
geographical zone 1A : Gibbonsville , Mulian , Banks , Haily , Ketchum , Monpelier , Aston , Victor Zone 2A : Rexburg , Idaho Falls , Rogerson , Pocatello , Sandpoint , Priest River , Salmon , Carey , Arco Zone 2B : Grangeville , Bonners Ferry , Weiser , Caldwell , Burley , Glenns Ferry , Shoshone , Twin Falls Zone 3A : Boise , Orofino , Kamish Zone 3B : Lewiston
AHS Heat Zones
in the main speaking , Idaho ’s summers are not overly hot , but the EL and parallel can move how long or warm the summertime can become . The American Horticultural Society ( AHS ) created 12 high temperature - zones that let out how many days above 86 degree F can be expect on average . The amount of heat can affect how well lovesome - season crops ( like watermelon vine or tomatoes ) will grow over summer , or whether or not cool - time of year plants ( like mountain alpine wildflowers or lettuce , radish ) are a good pick . Idaho generally has more summertime heat in the depleted elevation and more to the southwesterly parts of the body politic . The state admit AHS heat energy zones 8 through 2 , meaning between 1 and 120 days above 86 grade F can occur . The in high spirits the elevation , or more northerly or easterly in the state you are , the fewer quick days each summertime .
Idaho Cooperative Extension Services
Each county contains a arm business office of the University of Idaho ’s Extension Service , which serve spread horticulture inquiry information and recommendations to all parts of the state . meet the horticulture agent or passkey gardener in your county to get answers quickly about specific climate , soils or planting geographical zone information .
Effects of Microclimates
Microclimates are created when buildings , mountains , trees or other object create " warmer " or " colder " areas in the even garden circumstance . The USDA , Sunset and AHS zone assignment are all modified by local features . For example , a low - lying vale collects cold air , while a hillside tend to persist frost - free longer . Or , a declamatory pond or lake can in effect guard off a frost in fall with added heating , but keep things colder in spring when the water is gelid or cold than the breeze . Moreover , southward - facing wall and foundations collect heat from the sun , and groves can harbour cold wintertime winds . In summer , shade from Sir Herbert Beerbohm Tree and buildings can also keep a garden cooler than fence in areas .
