Frost dates · USDA zone 9b
Frost dates for Union City, CA
Union City, CA sees its last 32 °F night of spring around January 2 and its first of fall around December 25 — 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 13 (prior winter) | Jan 20 (next year) |
| Median — 1 year in 2 | Jan 2 | Dec 25 |
| 1 year in 10 | Jan 27 | Dec 6 |
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 338 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.
Union City planting calendar, 2027
Every row runs from the median last frost (Jan 2) and median first frost (Dec 25) 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 10 | Dec 5 | Mar 25 | 110 from transplant |
| Mustard greensGarnet Giant (Brassica juncea) | Direct sow | Jan 2 | Feb 1 | 30 from sow |
| CilantroSlow Bolt (Coriandrum sativum) | Dec 19 | Dec 19 | Feb 2 | 45 from sow |
| Genovese BasilGenovese | Dec 5 | Jan 16 | Mar 17 | 60 from transplant |
| CayenneLong Slim Cayenne (Capsicum annuum) | Nov 7 | Jan 9 | Mar 25 | 75 from transplant |
| HabaneroOrange Habanero (Capsicum chinense) | Oct 24 | Jan 16 | Apr 21 | 95 from transplant |
| JalapeñoEarly Jalapeño (Capsicum annuum) | Nov 7 | Jan 9 | Mar 25 | 75 from transplant |
| Marconi Red PepperMarconi Red (Capsicum annuum) | Nov 7 | Jan 9 | Mar 30 | 80 from transplant |
| SerranoSerrano Tampiqueño (Capsicum annuum) | Nov 7 | Jan 9 | Mar 30 | 80 from transplant |
| Nantes CarrotScarlet Nantes | Dec 19 | Dec 19 | Feb 27 | 70 from sow |
| TomatilloToma Verde | Nov 21 | Jan 9 | Mar 20 | 70 from transplant |
| Roma TomatoRoma VF (determinate paste) | Nov 21 | Jan 9 | Mar 25 | 75 from transplant |
| San Marzano TomatoSan Marzano (indeterminate paste) | Nov 21 | Jan 9 | Mar 30 | 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 Union City grow?
Each sauce, scheduled for a Union City container garden: when the first seeds go in and when enough fruit has ripened for one batch.
Union City frost questions
When is the last frost in Union City, CA?
The median last 32 °F freeze at HAYWARD AIR TERMINAL, CA is January 2: half of years see a later one. One year in ten, a freeze still comes after January 27; nine years in ten, it comes after December 13 (prior winter). Source: NOAA NCEI 1991–2020 U.S. Climate Normals.
When is the first frost in Union City, CA?
The median first 32 °F freeze of fall is December 25. One year in ten it arrives before December 6; nine years in ten, before January 20 (next year).
How long is the growing season in Union City, CA?
NOAA counts a full 365-day freeze-free season at HAYWARD AIR TERMINAL, 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 Union City, CA?
USDA hardiness zone 9b, per the 2023 USDA Plant Hardiness Zone Map for ZIP 94544. 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 Union City, CA?
Start Roma VF (determinate paste) seeds indoors around Nov 21 and transplant around Jan 9, 1 week after the median last frost. To cut the freeze risk to one year in ten, wait for Jan 27. First ripe fruit lands around Mar 25.
When should I plant peppers in Union City, CA?
Sow jalapeño indoors on a heat mat around Nov 7; transplant no earlier than Jan 9, and wait past it until nights hold above 50 °F — that can run weeks later. First green pods around Mar 25.
Nearby in California
- Haywardlast frost Jan 2
- Newarklast frost Jan 1
- Fremontlast frost Jan 1
- Pleasantonlast frost Feb 15
- Dublinlast frost Feb 15
- San Leandrolast frost Jan 7
All California frost dates → · How frost-date math drives a sowing calendar →