Union City, CA frost dates
Frost is light and occasional here — typically a few cold nights around midwinter (about 3 a year). Cover tender plants when frost is forecast.
How Union City compares
- In a typical year, frost nights in Union City fall between December 22 and January 7. In 1 year in 10 the first frost comes as early as December 2, or the last frost as late as February 7.
- Union City shares its weather station with Fremont, CA, 7 km away, so the two have the same frost dates.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | December 14 |
| 50% (median) | January 7 |
| 10% (safe for tender plants) | February 7 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | December 2 |
| 50% (median) | December 22 |
| 90% (late) | January 21 |
Frost here means 32°F (0°C). A median date means half of years have their last frost earlier and half later.
Gardening where frost is rare
Union City, CA only freezes on a few winter nights, so the usual "plant after the last frost" rule doesn't apply. Heat and rainfall decide the seasons instead:
- Cool-season crops (lettuce, broccoli, peas, carrots) grow best from fall through late winter.
- Warm-season crops (tomatoes, peppers, beans, squash) do best planted in late winter to spring, and again in late summer for a fall crop — midsummer heat can stop tomatoes setting fruit.
- Heat lovers (okra, sweet potatoes, melons) can be planted through spring and early summer.
About these dates
Based on 1991–2020 NOAA climate normals for the Fremont, CA weather station, 6 km away (elevation 39 ft (12 m)).
Frost dates near Union City
- Newark Jan 7 · Dec 22
- Fremont Jan 7 · Dec 22
- Hayward Jan 2 · Dec 25
- San Lorenzo Jan 2 · Dec 25
- Castro Valley Jan 2 · Dec 25
- Sunol Feb 15 · Dec 2
- San Leandro Jan 2 · Dec 25
- Pleasanton Feb 15 · Dec 2
- Dublin Feb 15 · Dec 2
- Palo Alto Feb 1 · Dec 7
Frequently asked questions
When is the last frost in Union City, CA?
The median last spring frost in Union City, CA is January 7. There is still about a 10% chance of frost after February 7, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Union City, CA?
The median first fall frost is December 22, with about a 10% chance of frost before December 2.
How long is the growing season in Union City, CA?
About 349 days between the median last spring frost and first fall frost.
What planting zone is Union City, CA?
Union City, CA is in USDA hardiness zone 10a.