Frost dates · USDA zone 10a
Frost dates for Ontario, CA
Ontario, CA sees its last 32 °F night of spring around January 4 and its first of fall around December 30 — a 365-day freeze-free season in a typical year.
Pick a sauce; the Plan Builder runs this station's dates and hands back the calendar, plant count and gear list.
Freeze odds, by date
| Odds | Last spring freeze after | First fall freeze before |
|---|---|---|
| 9 years in 10 | Dec 14 (prior winter) | Feb 1 (next year) |
| Median — 1 year in 2 | Jan 4 | Dec 30 |
| 1 year in 10 | Feb 7 | Dec 11 |
The top row is the risky edge: in 9 years of 10 a spring freeze still comes after it, so tender transplants set out then need cover. The bottom row is the cautious date — only 1 year in 10 freezes after it — and the one to plan uncovered tender transplants against. Freeze-free season: 365 days median, at least 339 in 9 years of 10, no freeze at all in 1 year of 10. NOAA ranks season length year by year, so it is not the gap between two rows above.
Ontario planting calendar, 2027
Every row runs from the median last frost (Jan 4) and median first frost (Dec 30) above, using each cultivar's days to maturity. Same engine as the Plan Builder.
| Crop | Start indoors | Transplant / plant | First harvest | Days |
|---|---|---|---|---|
| Hardneck GarlicSiberian (porcelain hardneck) | — | Oct 15prior fall | Jun 12 | 240 from sow |
| Spanish OnionYellow Sweet Spanish (long-day) | Oct 12 | Dec 7 | Mar 27 | 110 from transplant |
| Mustard greensGarnet Giant (Brassica juncea) | Direct sow | Jan 4 | Feb 3 | 30 from sow |
| CilantroSlow Bolt (Coriandrum sativum) | Dec 21 | Dec 21 | Feb 4 | 45 from sow |
| Genovese BasilGenovese | Dec 7 | Jan 18 | Mar 19 | 60 from transplant |
| CayenneLong Slim Cayenne (Capsicum annuum) | Nov 9 | Jan 11 | Mar 27 | 75 from transplant |
| HabaneroOrange Habanero (Capsicum chinense) | Oct 26 | Jan 18 | Apr 23 | 95 from transplant |
| JalapeñoEarly Jalapeño (Capsicum annuum) | Nov 9 | Jan 11 | Mar 27 | 75 from transplant |
| Marconi Red PepperMarconi Red (Capsicum annuum) | Nov 9 | Jan 11 | Apr 1 | 80 from transplant |
| SerranoSerrano Tampiqueño (Capsicum annuum) | Nov 9 | Jan 11 | Apr 1 | 80 from transplant |
| Nantes CarrotScarlet Nantes | Dec 21 | Dec 21 | Mar 1 | 70 from sow |
| TomatilloToma Verde | Nov 23 | Jan 11 | Mar 22 | 70 from transplant |
| Roma TomatoRoma VF (determinate paste) | Nov 23 | Jan 11 | Mar 27 | 75 from transplant |
| San Marzano TomatoSan Marzano (indeterminate paste) | Nov 23 | Jan 11 | Apr 1 | 80 from transplant |
Tight means first harvest lands within two weeks of the median first fall frost: start that crop indoors on time or cover it in fall.
What sauce can Ontario grow?
Each sauce, scheduled for a Ontario container garden: when the first seeds go in and when enough fruit has ripened for one batch.
Ontario frost questions
When is the last frost in Ontario, CA?
The median last 32 °F freeze at ONTARIO INTL AP, CA is January 4: half of years see a later one. One year in ten, a freeze still comes after February 7; nine years in ten, it comes after December 14 (prior winter). Source: NOAA NCEI 1991–2020 U.S. Climate Normals.
When is the first frost in Ontario, CA?
The median first 32 °F freeze of fall is December 30. One year in ten it arrives before December 11; nine years in ten, before February 1 (next year).
How long is the growing season in Ontario, CA?
NOAA counts a full 365-day freeze-free season at ONTARIO INTL AP, CA in a typical year. What limits a sauce garden here is heat: peppers and tomatoes drop flowers in sustained hot nights, so plant to finish before peak summer or after it breaks.
What growing zone is Ontario, CA?
USDA hardiness zone 10a, per the 2023 USDA Plant Hardiness Zone Map for ZIP 91761. A zone describes the coldest winter night, not when frost ends, so it is the wrong number for a planting calendar — the frost dates on this page are the right one.
When should I plant tomatoes in Ontario, CA?
Start Roma VF (determinate paste) seeds indoors around Nov 23 and transplant around Jan 11, 1 week after the median last frost. To cut the freeze risk to one year in ten, wait for Feb 7. First ripe fruit lands around Mar 27.
When should I plant peppers in Ontario, CA?
Sow jalapeño indoors on a heat mat around Nov 9; transplant no earlier than Jan 11, and wait past it until nights hold above 50 °F — that can run weeks later. First green pods around Mar 27.
Nearby in California
- Chinolast frost Jan 17
- Eastvalelast frost Jan 17
- Uplandlast frost Jan 4
- Rancho Cucamongalast frost Jan 4
- Jurupa Valleylast frost Jan 9
- Pomonalast frost Jan 8
All California frost dates → · How frost-date math drives a sowing calendar →