Rialto, California: planting zone & frost dates
Rialto 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 Feb 10 and the first fall frost around Dec 11.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | Feb 28 | Dec 1 |
| Typical planning date (30% risk) | Feb 10 | Dec 11 |
| Median (50%) | Jan 27 | Dec 19 |
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 REDLANDS, CA (USC00047306), 12.4 mi (20.0 km) from the city center and 62 ft higher than the city center (+19 m). Record used for the 1991–2020 normals: 18 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Rialto
All 5 ZIP codes covering Rialto are in zone 10a.
Vegetable planting calendar for Rialto
Dates are counted from the 30%-risk frost dates above (last frost Feb 10, first frost Dec 11). Shift a week later in cold spots or low-lying ground.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato | Dec 16 – Dec 30 | Feb 17 – Mar 3 | — | — |
| Pepper | Dec 2 – Dec 16 | Feb 24 – Mar 10 | — | — |
| Lettuce Mild winters: fall and winter plantings are usually more reliable than spring. | Dec 30 – Jan 13 | Jan 27 – Feb 17 | Jan 13 – Feb 24 | Oct 2 – Oct 30 |
| Green Beans | — | — | Feb 17 – Mar 24 | Sep 18 – Oct 2 |
| Sweet Corn | — | — | Feb 17 – Mar 17 | — |
| Zucchini & Summer Squash | Jan 13 – Jan 20 | Feb 17 – Mar 3 | Feb 17 – Mar 10 | Sep 18 – Oct 2 |
| Cucumber | Jan 13 – Jan 20 | Feb 24 – Mar 3 | Feb 17 – Mar 10 | Sep 18 – Oct 2 |
| Carrot Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Jan 20 – Feb 24 | Sep 18 – Oct 2 |
| Onion Mild winters: fall and winter plantings are usually more reliable than spring. | Nov 18 – Dec 2 | Jan 13 – Jan 27 | — | — |
| Potato Mild winters: fall and winter plantings are usually more reliable than spring. | — | Jan 13 – Feb 3 | — | — |
| Basil | Dec 30 – Jan 13 | Feb 24 – Mar 10 | Feb 24 – Mar 17 | — |
| Spinach Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Dec 30 – Jan 27 | Oct 16 – Nov 13 |
| Kale Mild winters: fall and winter plantings are usually more reliable than spring. | Dec 16 – Dec 30 | Jan 13 – Feb 3 | Jan 13 – Feb 3 | Oct 2 – Oct 30 |
| Broccoli Mild winters: fall and winter plantings are usually more reliable than spring. | Dec 16 – Dec 30 | Jan 27 – Feb 17 | — | Sep 18 – Oct 2 |
| Peas Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Dec 30 – Jan 20 | Oct 2 – Oct 16 |
| Eggplant | Dec 2 – Dec 16 | Feb 24 – Mar 10 | — | — |
| Cabbage Mild winters: fall and winter plantings are usually more reliable than spring. | Dec 16 – Dec 30 | Jan 13 – Jan 27 | — | Sep 18 – Oct 2 |
| Radish Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Jan 6 – Feb 24 | Oct 30 – Nov 27 |
| Strawberry | — | Jan 13 – Feb 3 | — | — |
| Beets Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Jan 20 – Mar 3 | Oct 2 – Oct 16 |
Nearby cities in California
- Fontana — zone 10a, last frost Jan 13, first frost Dec 22
- San Bernardino — zone 10a, last frost Feb 10, first frost Dec 11
- Jurupa Valley — zone 10a, last frost Jan 29, first frost Dec 19
- Rancho Cucamonga — zone 10a, last frost Jan 13, first frost Dec 22
- Riverside — zone 10a, last frost Jan 25, first frost Dec 15
- Ontario — zone 10a, last frost Jan 13, first frost Dec 22
More: all California cities · other zone 10a cities: Los Angeles, CA, Oakland, CA, Tampa, FL, Orlando, FL, Riverside, CA, Corpus Christi, TX, Port St. Lucie, FL, Scottsdale, AZ
Rialto gardening questions
When is the last frost in Rialto, CA?
Plan around Feb 10. At NOAA's Redlands, CA station, 12.4 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 27, and after Feb 28 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Jan 7. Springs here are erratic: 69 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 Rialto, CA?
Start seeds indoors Dec 16 – Dec 30 and set transplants outside Feb 17 – Mar 3, once nights stay above 50°F and the soil is near 60°F. With about 304 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 Rialto?
About 329 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 292 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 11. That ranks 58th longest of 84 California cities on this site.
When should I plant a fall garden in Rialto?
Count back from the first fall frost (Dec 11): transplant broccoli Sep 18 – Oct 2; sow kale Oct 2 – Oct 30; sow lettuce Oct 2 – Oct 30; sow radishes Oct 30 – Nov 27. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Jan 1. How the math works: succession and fall planting.
Did Rialto's hardiness zone change on the 2023 map?
No. Going by the zone that covers most of the city's land, Rialto is zone 10a on both the 2012 and the 2023 USDA maps (PRISM/OSU ZIP listings). About 42% of U.S. ZIP codes kept their half-zone in 2023. Why the 2023 map is warmer.
How does Rialto compare with Fontana, CA?
Both are in zone 10a. The typical last spring frost in Rialto (Feb 10) comes about 28 days later than in Fontana, CA (Jan 13), 4 miles away, and the first fall frost is Dec 11 versus Dec 22. The two cities use different NOAA stations.