Riverside, California: planting zone & frost dates
Riverside is in USDA plant hardiness zone 10a, where the average coldest winter night reaches 30 to 35°F (-1.1 to 1.7°C). The typical last spring frost is around Jan 25 and the first fall frost around Dec 15.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | Feb 25 | Dec 1 |
| Typical planning date (30% risk) | Jan 25 | Dec 15 |
| Median (50%) | Jan 9 | Dec 25 |
How to read this: after the spring "10% risk" date, a 32°F frost happens in only about 1 year in 10. In fall, the "10% risk" date is the early end — a frost before it happens about 1 year in 10.
Frost data comes from NOAA station RIVERSIDE FIRE STN 3, CA (USC00047470), 0.9 mi (1.5 km) from the city center and 52 ft lower than the city center (-16 m). Record used for the 1991–2020 normals: 21 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Riverside
Riverside spans more than one half-zone. Share of the city's land area by zone (via its 8 ZIP codes): 10a (91%), 9b (9%). The headline zone is the one covering the most land. Look up your ZIP for your exact zone.
Vegetable planting calendar for Riverside
Dates are counted from the 30%-risk frost dates above (last frost Jan 25, first frost Dec 15). Shift a week later in cold spots or low-lying ground.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato | Nov 30 – Dec 14 | Feb 1 – Feb 15 | — | — |
| Pepper | Nov 16 – Nov 30 | Feb 8 – Feb 22 | — | — |
| Lettuce Mild winters: fall and winter plantings are usually more reliable than spring. | Dec 14 – Dec 28 | Jan 11 – Feb 1 | Dec 28 – Feb 8 | Oct 6 – Nov 3 |
| Green Beans | — | — | Feb 1 – Mar 8 | Sep 22 – Oct 6 |
| Sweet Corn | — | — | Feb 1 – Mar 1 | — |
| Zucchini & Summer Squash | Dec 28 – Jan 4 | Feb 1 – Feb 15 | Feb 1 – Feb 22 | Sep 22 – Oct 6 |
| Cucumber | Dec 28 – Jan 4 | Feb 8 – Feb 15 | Feb 1 – Feb 22 | Sep 22 – Oct 6 |
| Carrot Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Jan 4 – Feb 8 | Sep 22 – Oct 6 |
| Onion Mild winters: fall and winter plantings are usually more reliable than spring. | Nov 2 – Nov 16 | Dec 28 – Jan 11 | — | — |
| Potato Mild winters: fall and winter plantings are usually more reliable than spring. | — | Dec 28 – Jan 18 | — | — |
| Basil | Dec 14 – Dec 28 | Feb 8 – Feb 22 | Feb 8 – Mar 1 | — |
| Spinach Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Dec 14 – Jan 11 | Oct 20 – Nov 17 |
| Kale Mild winters: fall and winter plantings are usually more reliable than spring. | Nov 30 – Dec 14 | Dec 28 – Jan 18 | Dec 28 – Jan 18 | Oct 6 – Nov 3 |
| Broccoli Mild winters: fall and winter plantings are usually more reliable than spring. | Nov 30 – Dec 14 | Jan 11 – Feb 1 | — | Sep 22 – Oct 6 |
| Peas Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Dec 14 – Jan 4 | Oct 6 – Oct 20 |
| Eggplant | Nov 16 – Nov 30 | Feb 8 – Feb 22 | — | — |
| Cabbage Mild winters: fall and winter plantings are usually more reliable than spring. | Nov 30 – Dec 14 | Dec 28 – Jan 11 | — | Sep 22 – Oct 6 |
| Radish Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Dec 21 – Feb 8 | Nov 3 – Dec 1 |
| Strawberry | — | Dec 28 – Jan 18 | — | — |
| Beets Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Jan 4 – Feb 15 | Oct 6 – Oct 20 |
Nearby cities in California
- Jurupa Valley — zone 10a, last frost Jan 29, first frost Dec 19
- Rialto — zone 10a, last frost Feb 10, first frost Dec 11
- Fontana — zone 10a, last frost Jan 13, first frost Dec 22
- Moreno Valley — zone 9b, last frost Feb 10, first frost Dec 11
- Corona — zone 10a, last frost Jan 29, first frost Dec 19
- San Bernardino — zone 10a, last frost Feb 10, first frost Dec 11
More: all California cities · other zone 10a cities: Los Angeles, CA, Oakland, CA, Tampa, FL, Orlando, FL, Corpus Christi, TX, Port St. Lucie, FL, Scottsdale, AZ, Santa Clarita, CA
Riverside gardening questions
When is the last frost in Riverside, CA?
Plan around Jan 25. At NOAA's Riverside Fire Stn 3, CA station, 0.9 mi from the city center, there is a 30% chance of a 32°F frost after that date. Half of springs have their last frost by Jan 9, and after Feb 25 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Dec 31. Springs here are erratic: 71 days separate the 90% and 10% dates, versus a median of 36 days for cities on this site, so watch the forecast rather than the calendar.
When should I plant tomatoes in Riverside, CA?
Start seeds indoors Nov 30 – Dec 14 and set transplants outside Feb 1 – Feb 15, once nights stay above 50°F and the soil is near 60°F. With about 324 frost-free days, frost is not the main limit — fruit set drops when nights stay above about 75°F, so early plantings tend to do best. More: tomato planting dates by zone.
How long is the growing season in Riverside?
About 353 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 307 days, and in 1 year in 10 it runs 365 days or more. In fall there is a 10% chance of frost by Dec 1 and a 30% chance by Dec 15. That ranks 34th longest of 84 California cities on this site.
When should I plant a fall garden in Riverside?
Count back from the first fall frost (Dec 15): transplant broccoli Sep 22 – Oct 6; sow kale Oct 6 – Nov 3; sow lettuce Oct 6 – Nov 3; sow radishes Nov 3 – Dec 1. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Dec 29. How the math works: succession and fall planting.
Did Riverside's hardiness zone change on the 2023 map?
Yes. Most of Riverside was zone 9b on the 2012 map and is zone 10a on the 2023 map — half a zone warmer, like about 56% of U.S. ZIP codes. The shift comes from a newer 1991–2020 averaging period plus more weather stations and better mapping; it does not mean last frost comes earlier. Why the 2023 map is warmer.
Is all of Riverside in zone 10a?
No. Zone 10a covers about 91% of the city's land; the rest is in 9b (9%), measured across the city's 8 ZIP codes. Check your own ZIP code in the table above or with the ZIP lookup.