Simi Valley, California: planting zone & frost dates
Simi Valley 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 12 and the first fall frost around Dec 6.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | Mar 5 | Nov 27 |
| Typical planning date (30% risk) | Feb 12 | Dec 6 |
| Median (50%) | Jan 24 | Dec 15 |
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 WOODLAND HILLS PIERCE COLLEGE, CA (USC00049785), 11.6 mi (18.6 km) from the city center and 89 ft lower than the city center (-27 m). Record used for the 1991–2020 normals: 24 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Simi Valley
All 2 ZIP codes covering Simi Valley are in zone 10a.
Vegetable planting calendar for Simi Valley
Dates are counted from the 30%-risk frost dates above (last frost Feb 12, first frost Dec 6). 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 18 – Jan 1 | Feb 19 – Mar 5 | — | — |
| Pepper | Dec 4 – Dec 18 | Feb 26 – Mar 12 | — | — |
| Lettuce Mild winters: fall and winter plantings are usually more reliable than spring. | Jan 1 – Jan 15 | Jan 29 – Feb 19 | Jan 15 – Feb 26 | Sep 27 – Oct 25 |
| Green Beans | — | — | Feb 19 – Mar 26 | Sep 13 – Sep 27 |
| Sweet Corn | — | — | Feb 19 – Mar 19 | — |
| Zucchini & Summer Squash | Jan 15 – Jan 22 | Feb 19 – Mar 5 | Feb 19 – Mar 12 | Sep 13 – Sep 27 |
| Cucumber | Jan 15 – Jan 22 | Feb 26 – Mar 5 | Feb 19 – Mar 12 | Sep 13 – Sep 27 |
| Carrot Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Jan 22 – Feb 26 | Sep 13 – Sep 27 |
| Onion Mild winters: fall and winter plantings are usually more reliable than spring. | Nov 20 – Dec 4 | Jan 15 – Jan 29 | — | — |
| Potato Mild winters: fall and winter plantings are usually more reliable than spring. | — | Jan 15 – Feb 5 | — | — |
| Basil | Jan 1 – Jan 15 | Feb 26 – Mar 12 | Feb 26 – Mar 19 | — |
| Spinach Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Jan 1 – Jan 29 | Oct 11 – Nov 8 |
| Kale Mild winters: fall and winter plantings are usually more reliable than spring. | Dec 18 – Jan 1 | Jan 15 – Feb 5 | Jan 15 – Feb 5 | Sep 27 – Oct 25 |
| Broccoli Mild winters: fall and winter plantings are usually more reliable than spring. | Dec 18 – Jan 1 | Jan 29 – Feb 19 | — | Sep 13 – Sep 27 |
| Peas Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Jan 1 – Jan 22 | Sep 27 – Oct 11 |
| Eggplant | Dec 4 – Dec 18 | Feb 26 – Mar 12 | — | — |
| Cabbage Mild winters: fall and winter plantings are usually more reliable than spring. | Dec 18 – Jan 1 | Jan 15 – Jan 29 | — | Sep 13 – Sep 27 |
| Radish Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Jan 8 – Feb 26 | Oct 25 – Nov 22 |
| Strawberry | — | Jan 15 – Feb 5 | — | — |
| Beets Mild winters: fall and winter plantings are usually more reliable than spring. | — | — | Jan 22 – Mar 5 | Sep 27 – Oct 11 |
Nearby cities in California
- Thousand Oaks — zone 10a, last frost Feb 12, first frost Dec 6
- Santa Clarita — zone 10a, last frost Jan 26, first frost Dec 20
- Santa Monica — zone 11a, frost rare
- Los Angeles — zone 10a, frost rare
- Burbank — zone 10a, last frost Jan 10, first frost Dec 16
- Oxnard — zone 10b, frost rare
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
Simi Valley gardening questions
When is the last frost in Simi Valley, CA?
Plan around Feb 12. At NOAA's Woodland Hills Pierce College, CA station, 11.6 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 24, and after Mar 5 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Dec 31. Springs here are erratic: 74 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 Simi Valley, CA?
Start seeds indoors Dec 18 – Jan 1 and set transplants outside Feb 19 – Mar 5, once nights stay above 50°F and the soil is near 60°F. With about 297 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 Simi Valley?
About 329 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 277 days, and in 1 year in 10 it runs 365 days or more. In fall there is a 10% chance of frost by Nov 27 and a 30% chance by Dec 6. That ranks 55th longest of 84 California cities on this site.
When should I plant a fall garden in Simi Valley?
Count back from the first fall frost (Dec 6): transplant broccoli Sep 13 – Sep 27; sow kale Sep 27 – Oct 25; sow lettuce Sep 27 – Oct 25; sow radishes Oct 25 – Nov 22. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Dec 26. How the math works: succession and fall planting.
Did Simi Valley's hardiness zone change on the 2023 map?
Yes. Most of Simi Valley 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.
How does Simi Valley compare with Santa Clarita, CA?
Both are in zone 10a. The typical last spring frost in Simi Valley (Feb 12) comes about 17 days later than in Santa Clarita, CA (Jan 26), 18 miles away, and the first fall frost is Dec 6 versus Dec 20. Simi Valley sits about 429 ft lower, which explains part of the gap. The two cities use different NOAA stations.