USDA zone 7a in Idaho
USDA plant hardiness zone 7a covers 23 locations across Idaho (average annual extreme minimum 0 to 5 °F): Banks, ID, Bliss, ID, Boise, ID, Boise, ID, Bruneau, ID, Buhl, ID, and 17 more. Average last spring frost across this group ranges April 17 (Bruneau) to June 1 (Banks), and growing seasons run 102–183 days (Banks to New Plymouth) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Idaho location's own frost dates; the printable planting calendar uses Glenns Ferry, this group's median-season location.
- USDA zone
- 7a0 to 5 °F
- Last frost range
- Apr 17–Jun 1avg, 32°F
- First frost range
- Sep 10–Oct 21avg, 32°F
- Growing season range
- 102–183days
Locations in this group
Every location below shares this zone and a nearby weather station, but keeps its own frost dates — find your town for its own numbers, or use the ZIP planner on the home page for an instant personalized answer.
| Location | Also covers | Nearest station | Last frost | First frost | Season (days) |
|---|---|---|---|---|---|
| Banks | — | Garden Valley | Jun 1 | Sep 10 | 102 |
| Bliss | Hagerman | Hagerman 2 Sw | May 3 | Oct 1 | 151 |
| Boise | Meridian, Robie Creek, Kuna, Garden | Boise Air Terminal | Apr 24 | Oct 21 | 179 |
| Boise | Hidden Springs, Horseshoe Bend | Boise 7 N | May 17 | Oct 12 | 147 |
| Bruneau | Hammett | Bruneau | Apr 17 | Oct 17 | 181 |
| Buhl | — | Castleford 2 N | May 17 | Sep 29 | 132 |
| Culdesac | — | Winchester | May 23 | Sep 25 | 121 |
| Eagle | Star, Middleton, Emmett, Horseshoe Bend, Letha | Emmett 2 E | Apr 30 | Oct 17 | 168 |
| Filer | — | Twin Falls Sun Vly Rgnl Ap | May 9 | Oct 4 | 147 |
| Glenns Ferry * | Hammett | Glenns Ferry | May 1 | Oct 3 | 154 |
| Grand View | — | Grand View 4 Nw | Apr 28 | Oct 6 | 162 |
| Homedale | Wilder | Homedale 1 Se | Apr 24 | Oct 9 | 169 |
| Homedale | Adrian | Owyhee Dam | May 7 | Oct 5 | 150 |
| Kamiah | — | Nezperce | May 24 | Sep 20 | 116 |
| Meridian | Nampa, Caldwell, Greenleaf, Notus | Nampa Sugar Factory | Apr 29 | Oct 13 | 164 |
| Mountain Home AFB | — | Mtn Home | May 2 | Oct 8 | 157 |
| New Plymouth | — | Payette | Apr 19 | Oct 20 | 183 |
| Orofino | Kendrick, Peck | Dworshak Fish Hatchery | Apr 20 | Oct 20 | 182 |
| Parma | — | Parma Exp Stn | Apr 27 | Oct 9 | 165 |
| Riggins | — | Riggins | May 6 | Oct 9 | 155 |
| Smiths Ferry | — | Ola | May 31 | Sep 16 | 108 |
| Stites | White Bird | Grangeville | May 9 | Oct 3 | 146 |
| Weiser | Cambridge | Cambridge | May 15 | Sep 27 | 134 |
* Glenns Ferry is this group's median-season location — the calendar below is computed from its data.
Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.
Planting calendar (Glenns Ferry, representative)
Computed from Glenns Ferry's average frost dates — the median-season location in this Idahozone 7a group. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees — your own location's dates may run a week or two earlier or later (see the table above).
- Start indoors
- Plant out
- Fall sowing
- First harvest
| Crop | Frost tolerance | Start indoors | Plant out | First harvest | Fall planting | Season fit |
|---|---|---|---|---|---|---|
| Tomato | Tender | Mar 6 – Mar 20 | May 8 – May 15 | Jul 7 – Jul 27 | — | matures comfortably |
| Pepper | Very tender | Feb 20 – Mar 6 | May 15 – May 22 | Jul 14 – Aug 13 | — | matures comfortably |
| Cucumber | Tender | Apr 3 – Apr 10 | May 8 – May 15 | Jun 27 – Jul 17 | — | matures comfortably |
| Summer squash / zucchini | Tender | — | May 8 – May 15 | Jun 22 – Jul 7 | — | matures comfortably |
| Bush bean | Tender | — | May 8 – May 15 | Jun 27 – Jul 7 | Aug 4 – Aug 14 | matures comfortably |
| Sweet corn | Tender | — | May 1 – May 15 | Jun 30 – Jul 30 | — | matures comfortably |
| Basil | Very tender | Mar 20 – Apr 3 | May 8 – May 15 | Jun 7 – Jun 22 | — | matures comfortably |
| Lettuce | Half-hardy | Mar 20 – Apr 3 | Apr 3 – Apr 17 | May 18 – Jun 2 | Jul 21 – Aug 5 | matures comfortably |
| Pea | Hardy | — | Mar 20 – Apr 3 | May 14 – May 29 | Jul 11 – Jul 26 | matures comfortably |
| Spinach | Hardy | — | Mar 20 – Apr 3 | Apr 29 – May 9 | Jul 31 – Aug 10 | matures comfortably |
| Carrot | Half-hardy | — | Apr 10 – Apr 17 | Jun 9 – Jun 29 | Jul 1 – Jul 21 | matures comfortably |
| Broccoli | Half-hardy | Mar 6 – Mar 20 | Apr 3 – Apr 17 | May 28 – Jun 17 | Jul 6 – Jul 26 | matures comfortably |
Which crops fit this growing season
Using Glenns Ferry's own 154-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 12 of 12 crops mature here with comfortable margin. A different location in the table above with a longer or shorter season will get a different mix — the ZIP planner on the home page gives your own.
Frost & freeze dates (Glenns Ferry)
From NOAA's 1991–2020 Climate Normals at station USC00103631. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 — the conservative date to plant after or harvest before.
| Threshold | Last spring — avg | Last spring — 90%-safe | First fall — avg | First fall — 90%-safe | Season (days) |
|---|---|---|---|---|---|
| 36°F | May 15 | Jun 5 | Sep 21 | Oct 7 | 128 |
| 32°F (freeze) | May 1 | May 16 | Oct 3 | Oct 19 | 154 |
| 28°F | Apr 15 | May 2 | Oct 16 | Nov 1 | 184 |
| 24°F | Mar 25 | Apr 18 | Oct 29 | Nov 18 | 217 |
Growing degree days
Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. This group's median GDD (base 50°F) across all 23 locations is 2,709; Glenns Ferry's own reading is shown below.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 3,542 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 5,980 | cool-season crops (brassicas, greens) |
Hardiness zone 7a in Idaho
Zone 7a means an average annual extreme minimum winter temperature of about 0 to 5 °F on the USDA's 2023 map — the number that tells you which perennials, shrubs, and trees reliably survive an average winter here. It does not set your planting dates, which come from the frost calendar above. Idaho spans 8 hardiness zones in this dataset — see all Idaho locations for the full range, including zones4a, 4b, 5a, 5b, 6a, 6b, 7b.
Explore zone 7a in other states at zone 7a, or see all USDA hardiness zones.
Frequently asked questions
- What does USDA hardiness zone 7a mean in Idaho?
- Zone 7a means an average annual extreme minimum winter temperature of 0 to 5 °F — the standard USDA measure of which perennials survive winter. 23 locations in Idaho fall in this zone. It does not set planting dates; see the frost calendar below for that.
- Where in Idaho's zone 7a is the growing season longest?
- New Plymouth runs the longest season on this page at about 183 days; Banks is shortest at about 102 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.
- When should I plant tomatoes in Idaho's zone 7a?
- Using Glenns Ferry's frost dates (this page's median-season location): start seeds indoors about Mar 6 – Mar 20, then transplant outside about May 8 – May 15. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.
- Does every location in Idaho's zone 7a have the same frost dates?
- No — they do not all share a weather station, so frost dates vary by a week or more across the 23 locations listed (see the table above for each location's own dates).
Sources & method
Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020, one reading per location's own nearest station (see the table above). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to each location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.