Three Rivers, CA 93244 planting calendar
- USDA zone
- 9b25 to 30 °F
- Last frost
- Feb 5avg, 32°F
- First frost
- Dec 8avg, 32°F
- Growing season
- 307days
Three Rivers, California is in USDA plant hardiness zone 9b. Its average last spring frost is around February 5 and the first fall frost around December 8, giving a growing season of about 307 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.
Three Rivers planting calendar
Each crop's windows are counted from Three Rivers'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 | Jan 1 | Feb 12 – Feb 19 | Apr 13 – May 3 | — |
| Pepper | Very tender | Jan 1 | Feb 19 – Feb 26 | Apr 20 – May 20 | — |
| Cucumber | Tender | Jan 8 – Jan 15 | Feb 12 – Feb 19 | Apr 3 – Apr 23 | — |
| Summer squash / zucchini | Tender | — | Feb 12 – Feb 19 | Mar 29 – Apr 13 | — |
| Bush bean | Tender | — | Feb 12 – Feb 19 | Apr 3 – Apr 13 | Oct 9 – Oct 19 |
| Sweet corn | Tender | — | Feb 5 – Feb 19 | Apr 6 – May 6 | — |
| Basil | Very tender | Jan 1 – Jan 8 | Feb 12 – Feb 19 | Mar 14 – Mar 29 | — |
| Lettuce | Half-hardy | Jan 1 – Jan 8 | Jan 8 – Jan 22 | Feb 22 – Mar 9 | Sep 25 – Oct 10 |
| Pea | Hardy | — | Jan 1 – Jan 8 | Feb 25 – Mar 12 | Sep 15 – Sep 30 |
| Spinach | Hardy | — | Jan 1 – Jan 8 | Feb 10 – Feb 20 | Oct 5 – Oct 15 |
| Carrot | Half-hardy | — | Jan 15 – Jan 22 | Mar 16 – Apr 5 | Sep 5 – Sep 25 |
| Broccoli | Half-hardy | Jan 1 | Jan 8 – Jan 22 | Mar 4 – Mar 24 | Sep 10 – Sep 30 |
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 USC00044890. 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 | Mar 25 | Apr 17 | Nov 23 | Dec 8 | 247 |
| 32°F (freeze) | Feb 5 | Mar 20 | Dec 8 | Jan 8 | 307 |
| 28°F | Jan 5 | Feb 13 | Dec 22 | Jan 20 | 358 |
| 24°F | Dec 29 | Jan 14 | Dec 24 | Jan 7 | 365 |
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) | 5,719 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 9,146 | cool-season crops (brassicas, greens) |
Hardiness zone 9b
Three Rivers sits in USDA plant hardiness zone 9b on the 2023 map — meaning its average annual extreme minimum winter temperature is about 25 to 30 °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 9b, or see all USDA hardiness zones.
Frequently asked questions
- What USDA hardiness zone is Three Rivers?
- Three Rivers, California is in USDA plant hardiness zone 9b on the 2023 map (average annual extreme minimum temperature 25 to 30 °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 Three Rivers?
- The average (median) last spring frost at 32°F is around February 5, from NOAA's 1991–2020 climate normals at the nearest reporting station. Roughly one year in ten the last frost is as late as March 20, so wait until then before setting out frost-tender plants if you want to be safe.
- When is the first fall frost in Three Rivers?
- The average first fall frost at 32°F is around December 8. That leaves a growing season of about 307 days between the average last spring and first fall frosts.
- When should I start tomatoes in Three Rivers?
- Start tomato seeds indoors about Jan 1 and transplant them outside about Feb 12 – Feb 19, once the danger of frost has passed. Estimated first harvest is around Apr 13 – May 3.
- How long is the growing season in Three Rivers?
- About 307 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~February 5) and the average first fall frost (~December 8). 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 USC00044890 (Lemon Cove, 3.3 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.