Idaho, ID planting calendar
- USDA zone
- 6b−5 to 0 °F
- Last frost
- Jun 17avg, 32°F
- First frost
- Sep 5avg, 32°F
- Growing season
- 80days
Idaho, Idaho is in USDA plant hardiness zone 6b. Its average last spring frost is around June 17 and the first fall frost around September 5, giving a growing season of about 80 days (NOAA 1991–2020 normals, 32°F, median). Start tender crops like tomatoes and peppers indoors weeks before the last frost and set them out afterward; sow hardy crops such as peas, spinach, and lettuce before it. The planner below turns those frost dates into a printable per-crop planting calendar.
Idaho planting calendar
Each crop's windows are counted from Idaho's average frost dates. 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.
- Start indoors
- Plant out
- Fall sowing
- First harvest
| Crop | Frost tolerance | Start indoors | Plant out | First harvest | Fall planting |
|---|---|---|---|---|---|
| Tomato | Tender | Apr 22 – May 6 | Jun 24 – Jul 1 | Aug 23 – Sep 12 | — |
| Pepper | Very tender | Apr 8 – Apr 22 | Jul 1 – Jul 8 | Aug 30 – Sep 29 | — |
| Cucumber | Tender | May 20 – May 27 | Jun 24 – Jul 1 | Aug 13 – Sep 2 | — |
| Summer squash / zucchini | Tender | — | Jun 24 – Jul 1 | Aug 8 – Aug 23 | — |
| Bush bean | Tender | — | Jun 24 – Jul 1 | Aug 13 – Aug 23 | Jul 7 – Jul 17 |
| Sweet corn | Tender | — | Jun 17 – Jul 1 | Aug 16 – Sep 15 | — |
| Basil | Very tender | May 6 – May 20 | Jun 24 – Jul 1 | Jul 24 – Aug 8 | — |
| Lettuce | Half-hardy | May 6 – May 20 | May 20 – Jun 3 | Jul 4 – Jul 19 | Jun 23 – Jul 8 |
| Pea | Hardy | — | May 6 – May 20 | Jun 30 – Jul 15 | Jun 13 – Jun 28 |
| Spinach | Hardy | — | May 6 – May 20 | Jun 15 – Jun 25 | Jul 3 – Jul 13 |
| Carrot | Half-hardy | — | May 27 – Jun 3 | Jul 26 – Aug 15 | Jun 3 – Jun 23 |
| Broccoli | Half-hardy | Apr 22 – May 6 | May 20 – Jun 3 | Jul 14 – Aug 3 | Jun 8 – Jun 28 |
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.
Frost & freeze dates
From NOAA's 1991–2020 Climate Normals at station USC00104442. 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 (p10 for spring, p90 for fall) — 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 | — | — | — | — | 52 |
| 32°F (freeze) | Jun 17 | Jul 4 | Sep 5 | Sep 21 | 80 |
| 28°F | May 22 | Jun 14 | Sep 19 | Oct 5 | 117 |
| 24°F | May 3 | May 18 | Oct 3 | Oct 19 | 152 |
32°F is the standard "freeze" line that damages tender crops; lighter 36°F frost can nip the most cold-sensitive plants, while hardy crops shrug off light frost down toward 28°F. Use the threshold that matches what you are protecting.
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. Warm-season crops need a long, warm GDD total; a short, cool GDD total favors greens and brassicas.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 1,586 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 3,273 | cool-season crops (brassicas, greens) |
Hardiness zone 6b
Idaho sits in USDA plant hardiness zone 6b on the 2023 map — meaning its average annual extreme minimum winter temperature is about −5 to 0 °F. That number 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.
Explore more places in zone 6b, or see all USDA hardiness zones.
Frequently asked questions
- What USDA hardiness zone is Idaho?
- Idaho, Idaho is in USDA plant hardiness zone 6b on the 2023 map (average annual extreme minimum temperature −5 to 0 °F) — from the USDA Plant Hardiness Zone Map 2023, matched to this location's ZIP. See the methodology page for sources.
- When is the last frost in Idaho?
- The average (median) last spring frost at 32°F is around June 17, from NOAA's 1991–2020 climate normals at the nearest reporting station. Roughly one year in ten the last frost is as late as July 4, so wait until then before setting out frost-tender plants if you want to be safe.
- When is the first fall frost in Idaho?
- The average first fall frost at 32°F is around September 5. That leaves a growing season of about 80 days between the average last spring and first fall frosts.
- When should I start tomatoes in Idaho?
- Start tomato seeds indoors about Apr 22 – May 6 and transplant them outside about Jun 24 – Jul 1, once the danger of frost has passed. Estimated first harvest is around Aug 23 – Sep 12.
- How long is the growing season in Idaho?
- About 80 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~June 17) and the average first fall frost (~September 5). Cold-hardy crops extend usable time at both ends; frost-tender crops fit inside it.
Sources & method
Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020 for station USC00104442 (Idaho City, 6.8 km away). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to this 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.