Riggins, ID 83654 planting calendar
- USDA zone
- 6a−10 to −5 °F
- Last frost
- May 6avg, 32°F
- First frost
- Oct 9avg, 32°F
- Growing season
- 155days
Riggins, Idaho is in USDA plant hardiness zone 6a. Its average last spring frost is around May 6 and the first fall frost around October 9, giving a growing season of about 155 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.
Riggins planting calendar
Each crop's windows are counted from Riggins'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 | Mar 11 – Mar 25 | May 13 – May 20 | Jul 12 – Aug 1 | — |
| Pepper | Very tender | Feb 25 – Mar 11 | May 20 – May 27 | Jul 19 – Aug 18 | — |
| Cucumber | Tender | Apr 8 – Apr 15 | May 13 – May 20 | Jul 2 – Jul 22 | — |
| Summer squash / zucchini | Tender | — | May 13 – May 20 | Jun 27 – Jul 12 | — |
| Bush bean | Tender | — | May 13 – May 20 | Jul 2 – Jul 12 | Aug 10 – Aug 20 |
| Sweet corn | Tender | — | May 6 – May 20 | Jul 5 – Aug 4 | — |
| Basil | Very tender | Mar 25 – Apr 8 | May 13 – May 20 | Jun 12 – Jun 27 | — |
| Lettuce | Half-hardy | Mar 25 – Apr 8 | Apr 8 – Apr 22 | May 23 – Jun 7 | Jul 27 – Aug 11 |
| Pea | Hardy | — | Mar 25 – Apr 8 | May 19 – Jun 3 | Jul 17 – Aug 1 |
| Spinach | Hardy | — | Mar 25 – Apr 8 | May 4 – May 14 | Aug 6 – Aug 16 |
| Carrot | Half-hardy | — | Apr 15 – Apr 22 | Jun 14 – Jul 4 | Jul 7 – Jul 27 |
| Broccoli | Half-hardy | Mar 11 – Mar 25 | Apr 8 – Apr 22 | Jun 2 – Jun 22 | Jul 12 – Aug 1 |
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 USC00107706. 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 | May 29 | Jun 20 | Sep 27 | Oct 12 | 119 |
| 32°F (freeze) | May 6 | May 26 | Oct 9 | Oct 26 | 155 |
| 28°F | Apr 18 | May 5 | Oct 22 | Nov 7 | 185 |
| 24°F | Mar 27 | Apr 17 | Nov 3 | Nov 23 | 225 |
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) | 2,443 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 4,575 | cool-season crops (brassicas, greens) |
Hardiness zone 6a
Riggins sits in USDA plant hardiness zone 6a on the 2023 map — meaning its average annual extreme minimum winter temperature is about −10 to −5 °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 6a, or see all USDA hardiness zones.
Frequently asked questions
- What USDA hardiness zone is Riggins?
- Riggins, Idaho is in USDA plant hardiness zone 6a on the 2023 map (average annual extreme minimum temperature −10 to −5 °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 Riggins?
- The average (median) last spring frost at 32°F is around May 6, from NOAA's 1991–2020 climate normals at the nearest reporting station. Roughly one year in ten the last frost is as late as May 26, so wait until then before setting out frost-tender plants if you want to be safe.
- When is the first fall frost in Riggins?
- The average first fall frost at 32°F is around October 9. That leaves a growing season of about 155 days between the average last spring and first fall frosts.
- When should I start tomatoes in Riggins?
- Start tomato seeds indoors about Mar 11 – Mar 25 and transplant them outside about May 13 – May 20, once the danger of frost has passed. Estimated first harvest is around Jul 12 – Aug 1.
- How long is the growing season in Riggins?
- About 155 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~May 6) and the average first fall frost (~October 9). 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 USC00107706 (Riggins, 17.8 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.