What Planting Zones Are in Idaho?
Idaho spans USDA hardiness zones 4a to 7b, where the average coldest winter night ranges from −30 °F to 10 °F (−34.4 °C to −12.2 °C). Zone 6b covers the most ZIP codes, 28%, and zones 5a to 7a together cover 98% of the state.
- Zone 4a<1% · 2 ZIPs
- Zone 4b<1% · 2 ZIPs
- Zone 5a13% · 41 ZIPs
- Zone 5b14% · 44 ZIPs
- Zone 6a17% · 52 ZIPs
- Zone 6b28% · 87 ZIPs
- Zone 7a26% · 82 ZIPs
- Zone 7b<1% · 3 ZIPs
Bars show each zone's share of the 313 Idaho ZIP codes in the official 2023 USDA ZIP code table; select a zone for its temperatures and hardy plants.
What Hardiness Zone Are Idaho Cities In?
Boise City is in zone 7a, Meridian is in zone 7a, Nampa is in zone 7a and Caldwell is in zone 7a. The table lists the zone, winter low and average frost dates for 18 Idaho cities, using the ZIP code nearest each city center.
| City | ZIP | Zone | Winter low | Last frost | First frost |
|---|---|---|---|---|---|
| Boise City | 83706 | 7a | 0 °F to 5 °F | Apr 24 | Oct 21 |
| Meridian | 83642 | 7a | 0 °F to 5 °F | Apr 24 | Oct 21 |
| Nampa | 83687 | 7a | 0 °F to 5 °F | Apr 29 | Oct 13 |
| Caldwell | 83605 | 7a | 0 °F to 5 °F | Apr 29 | Oct 13 |
| Idaho Falls | 83404 | 5b | −15 °F to −10 °F | May 9 | Oct 1 |
| Pocatello | 83209 | 6a | −10 °F to −5 °F | May 2 | Oct 11 |
| Coeur d'Alene | 83815 | 6b | −5 °F to 0 °F | Apr 22 | Oct 18 |
| Twin Falls | 83328 | 7a | 0 °F to 5 °F | Apr 25 | Oct 15 |
| Post Falls | 83854 | 6b | −5 °F to 0 °F | Apr 22 | Oct 18 |
| Rexburg | 83460 | 5a | −20 °F to −15 °F | May 12 | Sep 24 |
| Lewiston | 83501 | 7b | 5 °F to 10 °F | Apr 6 | Oct 26 |
| Moscow | 83844 | 6b | −5 °F to 0 °F | Apr 29 | Oct 2 |
| Mountain Home | 83648 | 7a | 0 °F to 5 °F | May 2 | Oct 8 |
| Blackfoot | 83221 | 5b | −15 °F to −10 °F | May 5 | Oct 3 |
| Burley | 83336 | 6b | −5 °F to 0 °F | May 7 | Oct 4 |
| Sandpoint | 83852 | 6b | −5 °F to 0 °F | May 8 | Sep 28 |
| Hailey | 83333 | 6a | −10 °F to −5 °F | May 13 | Oct 2 |
| Emmett | 83617 | 7a | 0 °F to 5 °F | Apr 30 | Oct 17 |
Zone: 2023 USDA ZIP code table for the ZIP code nearest each city's Census center point. Frost dates: 50% (median) dates from the nearest NOAA station, 1991–2020 normals. Cities: the largest Idaho places by 2024 Census population estimates, spread across the state, plus the largest place in each common zone. Large cities can span two half zones.
Which Parts of Idaho Are in Each Zone?
Zone 5a, the coldest Idaho zone with towns, covers 13% of ZIP codes around Rexburg, McCall and St. Anthony. Zone 7b, the warmest, covers <1% around Lewiston and Lapwai. The table lists the largest places in every zone.
| Zone | Avg. coldest night | Share of ZIPs | Largest places in this zone |
|---|---|---|---|
| Zone 4a | −30 °F to −25 °F | <1% (2) | Rural ZIP codes only |
| Zone 4b | −25 °F to −20 °F | <1% (2) | Rural ZIP codes only |
| Zone 5a | −20 °F to −15 °F | 13% (41) | Rexburg, McCall, St. Anthony, Soda Springs |
| Zone 5b | −15 °F to −10 °F | 14% (44) | Idaho Falls, Ammon, Blackfoot, Rigby |
| Zone 6a | −10 °F to −5 °F | 17% (52) | Pocatello, Hailey, Rupert, Preston |
| Zone 6b | −5 °F to 0 °F | 28% (87) | Coeur d'Alene, Post Falls, Moscow, Hayden |
| Zone 7a | 0 °F to 5 °F | 26% (82) | Boise City, Meridian, Nampa, Caldwell |
| Zone 7b | 5 °F to 10 °F | <1% (3) | Lewiston, Lapwai |
Places: incorporated places with 1,000+ residents, assigned the zone of the ZIP code nearest their Census center point.
What Do the Hardiness Zones Mean for Idaho Gardeners?
A Idaho gardener in zone 7b sees winter lows about 35 °F milder than one in zone 4a, so a shrub or perennial that thrives in one part of the state can die in another. Choose plants rated to your own ZIP code's zone or colder.
Hardiness zones follow latitude, elevation and large bodies of water rather than state lines. Higher ground and inland valleys that trap cold air usually sit in colder half zones, while cities, coasts and large lakes moderate winter lows. Within Idaho, a plant labelled “zones 5–7” survives winter in at least 98% of ZIP codes, but plants at the edge of their range benefit from mulch and a sheltered spot. Enter a ZIP code in the USDA hardiness zone finder by ZIP code to check your exact half zone before buying perennials.
A zone describes winter cold only. Summer heat, humidity, rainfall and soil decide whether a cold-hardy plant thrives, and planting dates for vegetables follow frost dates, not zones: two Idaho towns in the same zone can have last frosts weeks apart.
What Plants Grow Well Across Idaho?
198 plants in PlantoScan's catalogue are hardy in every zone from 5a to 7a, the zones that cover 98% of Idaho ZIP codes. Popular examples include hydrangea, peony and daisy.
Hydrangea
Hydrangea macrophylla
Zone 5 – 9
AI generated
Peony
Paeonia lactiflora
Zone 3 – 8
AI generated
- DaisyBellis perennisPlantoScan
Daisy
Bellis perennis
Zone 4a – 8b
Chrysanthemum
Chrysanthemum morifolium
Zone 5a – 9b
PlantoscanAI generated
Poppy
Papaver somniferum
Zone 3a – 9b
AI generated
Carnation
Dianthus caryophyllus
Zone 5a – 9b
AI generated
Daffodil
Narcissus poeticus
Zone 3 – 8
AI generated
Arugula
Eruca sativa
Zone 5a – 10b
AI generated
Alfalfa
Medicago sativa
Zone 3a – 10a
AI generated
Hardiness ranges come from PlantoScan's plant database; gardeners in Idaho's colder or warmer edge zones should check each plant's full range.
When Is the Last Frost in Idaho?
Across most Idaho ZIP codes, the average last spring frost falls between April 24 and June 12, from April 6 in Lewiston to May 13 in Hailey. Tender vegetables such as tomatoes go out 1 to 2 weeks after the local date.
The last and first frost dates for Idaho cities include the safer 90% planting date, the fall frost date, growing season length and a tomato planting table for each city.
Frequently Asked Questions
- What planting zone is Idaho?
- Idaho spans USDA hardiness zones 4a to 7b on the 2023 USDA Plant Hardiness Zone Map. Zone 6b is the most common, covering 28% of the state's 313 ZIP codes, and zones 5a to 7a together cover 98%.
- What hardiness zone is Boise City, Idaho?
- Boise City is in USDA hardiness zone 7a (ZIP 83706), where the average coldest winter night reaches 0 °F to 5 °F. Its average last spring frost is April 24 and its first fall frost October 21.
- What hardiness zone is Meridian, Idaho?
- Meridian is in USDA hardiness zone 7a (ZIP 83642), where the average coldest winter night reaches 0 °F to 5 °F. Its average last spring frost is April 24 and its first fall frost October 21.
- What hardiness zone is Nampa, Idaho?
- Nampa is in USDA hardiness zone 7a (ZIP 83687), where the average coldest winter night reaches 0 °F to 5 °F. Its average last spring frost is April 29 and its first fall frost October 13.
- What is the coldest hardiness zone in Idaho?
- Zone 4a (−30 °F to −25 °F) is the coldest zone in Idaho, found in 2 ZIP codes. The warmest is zone 7b (5 °F to 10 °F), around Lewiston and Lapwai.
Zones: 2023 USDA Plant Hardiness Zone Map ZIP code table, USDA Agricultural Research Service and the PRISM Climate Group, Oregon State University, used without changes. Frost dates: NOAA National Centers for Environmental Information, 1991–2020 U.S. Climate Normals. City locations and populations: U.S. Census Bureau Gazetteer files and Vintage 2024 population estimates. PlantoScan is not affiliated with or endorsed by these agencies.