Rancho Cucamonga, California: planting zone & frost dates
Rancho Cucamonga 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 13 and the first fall frost around Dec 22.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | Feb 7 | Dec 11 |
| Typical planning date (30% risk) | Jan 13 | Dec 22 |
| Median (50%) | Jan 4 | Dec 30 |
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 ONTARIO INTL AP, CA (USW00003102), 5.5 mi (8.8 km) from the city center and 469 ft lower than the city center (-143 m). Record used for the 1991–2020 normals: 14 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Rancho Cucamonga
All 4 ZIP codes covering Rancho Cucamonga are in zone 10a.
Vegetable planting calendar for Rancho Cucamonga
Dates are counted from the 30%-risk frost dates above (last frost Jan 13, first frost Dec 22). 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 18 – Dec 2 | Jan 20 – Feb 3 | — | — |
| Pepper | Nov 4 – Nov 18 | Jan 27 – Feb 10 | — | — |
| Lettuce Mild winters: fall and winter plantings are usually more reliable than spring. | Dec 2 – Dec 16 | Dec 30 – Jan 20 | Dec 16 – Jan 27 | Oct 13 – Nov 10 |
| Green Beans | — | — | Jan 20 – Feb 24 | Sep 29 – Oct 13 |
| Sweet Corn | — | — | Jan 20 – Feb 17 | — |
| Zucchini & Summer Squash | Dec 16 – Dec 23 | Jan 20 – Feb 3 | Jan 20 – Feb 10 | Sep 29 – Oct 13 |
| Cucumber | Dec 16 – Dec 23 | Jan 27 – Feb 3 | Jan 20 – Feb 10 | Sep 29 – Oct 13 |
| Carrot Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Dec 23 – Jan 27 | Sep 29 – Oct 13 |
| Onion Mild winters: fall and winter plantings are usually more reliable than spring. | Oct 21 – Nov 4 | Dec 16 – Dec 30 | — | — |
| Potato Mild winters: fall and winter plantings are usually more reliable than spring. | — | Dec 16 – Jan 6 | — | — |
| Basil | Dec 2 – Dec 16 | Jan 27 – Feb 10 | Jan 27 – Feb 17 | — |
| Spinach Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Dec 2 – Dec 30 | Oct 27 – Nov 24 |
| Kale Mild winters: fall and winter plantings are usually more reliable than spring. | Nov 18 – Dec 2 | Dec 16 – Jan 6 | Dec 16 – Jan 6 | Oct 13 – Nov 10 |
| Broccoli Mild winters: fall and winter plantings are usually more reliable than spring. | Nov 18 – Dec 2 | Dec 30 – Jan 20 | — | Sep 29 – Oct 13 |
| Peas Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Dec 2 – Dec 23 | Oct 13 – Oct 27 |
| Eggplant | Nov 4 – Nov 18 | Jan 27 – Feb 10 | — | — |
| Cabbage Mild winters: fall and winter plantings are usually more reliable than spring. | Nov 18 – Dec 2 | Dec 16 – Dec 30 | — | Sep 29 – Oct 13 |
| Radish Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Dec 9 – Jan 27 | Nov 10 – Dec 8 |
| Strawberry | — | Dec 16 – Jan 6 | — | — |
| Beets Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Dec 23 – Feb 3 | Oct 13 – Oct 27 |
Nearby cities in California
- Upland — zone 10a, last frost Jan 26, first frost Dec 19
- Ontario — zone 10a, last frost Jan 13, first frost Dec 22
- Fontana — zone 10a, last frost Jan 13, first frost Dec 22
- Jurupa Valley — zone 10a, last frost Jan 29, first frost Dec 19
- Rialto — zone 10a, last frost Feb 10, first frost Dec 11
- Chino — zone 10a, last frost Feb 3, first frost Dec 10
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
Rancho Cucamonga gardening questions
When is the last frost in Rancho Cucamonga, CA?
Plan around Jan 13. At NOAA's Ontario Int'l Airport, CA station, 5.5 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 4, and after Feb 7 the risk drops to about 1 in 10. Springs here are erratic: 55 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 Rancho Cucamonga, CA?
Start seeds indoors Nov 18 – Dec 2 and set transplants outside Jan 20 – Feb 3, once nights stay above 50°F and the soil is near 60°F. With about 343 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 Rancho Cucamonga?
About 365 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 339 days, and in 1 year in 10 it runs 365 days or more. In fall there is a 10% chance of frost by Dec 11 and a 30% chance by Dec 22. That ranks 8th longest of 84 California cities on this site.
When should I plant a fall garden in Rancho Cucamonga?
Count back from the first fall frost (Dec 22): transplant broccoli Sep 29 – Oct 13; sow kale Oct 13 – Nov 10; sow lettuce Oct 13 – Nov 10; sow radishes Nov 10 – Dec 8. How the math works: succession and fall planting.
Did Rancho Cucamonga's hardiness zone change on the 2023 map?
No. Going by the zone that covers most of the city's land, Rancho Cucamonga 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 Rancho Cucamonga compare with Upland, CA?
Both are in zone 10a. The typical last spring frost in Rancho Cucamonga (Jan 13) comes about 13 days earlier than in Upland, CA (Jan 26), 5 miles away, and the first fall frost is Dec 22 versus Dec 19. The two cities use different NOAA stations.