Three Rivers, CA 93271 planting calendar
- USDA zone
- 9b25 to 30 °F
- Last frost
- Mar 16avg, 32°F
- First frost
- Nov 26avg, 32°F
- Growing season
- 249days
Three Rivers, California is in USDA plant hardiness zone 9b. Its average last spring frost is around March 16 and the first fall frost around November 26, giving a growing season of about 249 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 19 – Feb 2 | Mar 23 – Mar 30 | May 22 – Jun 11 | — |
| Pepper | Very tender | Jan 5 – Jan 19 | Mar 30 – Apr 6 | May 29 – Jun 28 | — |
| Cucumber | Tender | Feb 16 – Feb 23 | Mar 23 – Mar 30 | May 12 – Jun 1 | — |
| Summer squash / zucchini | Tender | — | Mar 23 – Mar 30 | May 7 – May 22 | — |
| Bush bean | Tender | — | Mar 23 – Mar 30 | May 12 – May 22 | Sep 27 – Oct 7 |
| Sweet corn | Tender | — | Mar 16 – Mar 30 | May 15 – Jun 14 | — |
| Basil | Very tender | Feb 2 – Feb 16 | Mar 23 – Mar 30 | Apr 22 – May 7 | — |
| Lettuce | Half-hardy | Feb 2 – Feb 16 | Feb 16 – Mar 2 | Apr 2 – Apr 17 | Sep 13 – Sep 28 |
| Pea | Hardy | — | Feb 2 – Feb 16 | Mar 29 – Apr 13 | Sep 3 – Sep 18 |
| Spinach | Hardy | — | Feb 2 – Feb 16 | Mar 14 – Mar 24 | Sep 23 – Oct 3 |
| Carrot | Half-hardy | — | Feb 23 – Mar 2 | Apr 24 – May 14 | Aug 24 – Sep 13 |
| Broccoli | Half-hardy | Jan 19 – Feb 2 | Feb 16 – Mar 2 | Apr 12 – May 2 | Aug 29 – Sep 18 |
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 USC00048917. 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 | Apr 13 | May 4 | Nov 10 | Nov 25 | 209 |
| 32°F (freeze) | Mar 16 | Apr 14 | Nov 26 | Dec 12 | 249 |
| 28°F | Jan 30 | Mar 18 | Dec 11 | Jan 11 | 317 |
| 24°F | Jan 3 | Feb 7 | Dec 26 | Jan 30 | 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) | 4,996 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 8,271 | 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 March 16, from NOAA's 1991–2020 climate normals at the nearest reporting station. Roughly one year in ten the last frost is as late as April 14, 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 November 26. That leaves a growing season of about 249 days between the average last spring and first fall frosts.
- When should I start tomatoes in Three Rivers?
- Start tomato seeds indoors about Jan 19 – Feb 2 and transplant them outside about Mar 23 – Mar 30, once the danger of frost has passed. Estimated first harvest is around May 22 – Jun 11.
- How long is the growing season in Three Rivers?
- About 249 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~March 16) and the average first fall frost (~November 26). 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 USC00048917 (Three Rivers Edison Ph 1, 3.2 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.