Union City, CA planting zone & frost dates
Union City is in USDA hardiness zone 9b. The last spring frost usually comes around January 7 and the first fall frost around December 22, for a growing season of about 353 days.
Planting calendar for Union City
Dates are counted from the average last spring frost (January 7) using the typical timing recommended by U.S. extension services. Warm-season crops go out only after the danger of frost has passed and the soil has warmed.
| Crop | When |
|---|---|
| Tomatoes | Start seeds indoors: Nov 12 – Nov 26 Transplant outdoors: Jan 14 – Jan 21 |
| Peppers | Start seeds indoors: Oct 29 – Nov 12 Transplant outdoors: Jan 21 – Jan 28 |
| Eggplant | Start seeds indoors: Oct 29 – Nov 12 Transplant outdoors: Jan 21 – Jan 28 |
| Broccoli | Start seeds indoors: Oct 29 – Nov 12 Transplant outdoors: Dec 10 – Dec 24 |
| Cabbage | Start seeds indoors: Oct 29 – Nov 12 Transplant outdoors: Dec 10 – Dec 24 |
| Onions (sets) | Plant outdoors: Dec 10 – Dec 24 |
| Peas | Sow outdoors: Nov 26 – Dec 10 |
| Spinach | Sow outdoors: Nov 26 – Dec 10 |
| Lettuce | Sow outdoors: Dec 10 – Dec 24 |
| Carrots | Sow outdoors: Dec 10 – Dec 24 |
| Potatoes | Plant outdoors: Dec 10 – Dec 24 |
| Beans | Sow outdoors: Jan 14 – Jan 21 |
| Sweet corn | Sow outdoors: Jan 14 – Jan 21 |
| Cucumbers | Sow outdoors: Jan 14 – Jan 21 |
| Squash & zucchini | Sow outdoors: Jan 14 – Jan 21 |
| Basil | Start seeds indoors: Nov 26 – Dec 10 Transplant outdoors: Jan 14 – Jan 21 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Oct 27 (8 weeks before the average first fall frost on Dec 22).
Useful for zone 9b gardens
- Seed starting kit with dome — to start seeds indoors before the last frost
- LED grow light for seedlings — stops leggy seedlings
- Frost cloth / plant covers — for late spring and early fall frosts
- Soil thermometer — warm-season crops need soil above 60°F
- Shade cloth — for hot summers
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Frost risk in detail
| 90% chance | 50% chance | 10% chance | |
|---|---|---|---|
| Last 32°F frost in spring is after | Dec 14 | Jan 7 | Feb 7 |
| First 32°F frost in fall is before | Jan 21 | Dec 22 | Dec 2 |
How to read it: in spring there is a 10% chance of a frost after February 7, so that is a safe date for tender plants. In fall there is a 10% chance of frost before December 2. A hard freeze (28°F) usually ends around December 31.
Hardiness zone by ZIP code in Union City
- 94587 zone 10a
Nearby cities
- Fremont zone 9b, last frost Jan 7
- Newark zone 10a
- Fairview zone 9b
- Hayward zone 10a
- Cherryland zone 10a
- Castro Valley zone 10a
- Dublin zone 9b, last frost Feb 15
- Ashland zone 10a
Questions
What growing zone is Union City, CA?
Union City is in USDA Plant Hardiness Zone 9b (average extreme winter low 25°F to 30°F), according to the USDA 2023 map. Some ZIP codes of the city fall in zone 10a.
When is the last frost in Union City?
The average last spring frost (32°F) in Union City is January 7. There is still a 10% chance of frost until February 7.
When can I plant tomatoes in Union City?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around Jan 14 – Jan 21. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Fremont, CA (USC00043244), 6.0 km (3.7 mi) from the city center, elevation 12 m, based on 18 years of records. Hardiness zone: USDA Plant Hardiness Zone Map 2023 for the ZIP code nearest to the city center. Microclimates (valleys, hills, cities, coasts) can be warmer or colder: check the local forecast before planting. How we calculate the data.