Frost Dates for Union City, CA
In Union City, CA, the average last spring frost is around Jan 7 and the average first fall frost around Dec 22, for a growing season of about 353 days. For frost-tender plants, wait until Feb 7, when the chance of frost drops to 10%.
Based on NOAA 1991–2020 records from the Fremont, CA weather station, 4 miles away, elevation 38 ft. Frost can come earlier in low spots and valleys and later near cities and large lakes.
Frost probability by date
Chance of a 32°F frost after the spring date, or before the fall date.
| Chance | Last spring frost | First fall frost |
|---|---|---|
| 10% | Feb 7 | Dec 2 |
| 20% | Jan 29 | Dec 7 |
| 30% | Jan 22 | Dec 12 |
| 40% | Jan 13 | Dec 16 |
| 50% | Jan 7 | Dec 22 |
| 60% | Jan 2 | Dec 27 |
| 70% | Dec 29 | Jan 1 |
| 80% | Dec 23 | Jan 7 |
| 90% | Dec 14 | Jan 21 |
Light frost vs. hard freeze
Average (50%) dates for each temperature. Tender plants are damaged at 36°F; most hardy crops survive until 28°F.
| Temperature | Last in spring | First in fall |
|---|---|---|
| Light frost (36°F) | Feb 6 | Dec 5 |
| Frost / freeze (32°F) | Jan 7 | Dec 22 |
| Hard freeze (28°F) | Dec 31 | Dec 29 |
Planting calendar for Union City
Transplant Jan 14 – Jan 28
Transplant Jan 21 – Feb 4
Transplant Jan 21 – Feb 4
Transplant Jan 14 – Jan 28
Sow or transplant Jan 14 – Jan 28
Sow or transplant Jan 14 – Jan 28
Sow or transplant Jan 21 – Feb 4
Sow or transplant Dec 10 – Dec 24
Fall sowing Oct 27 – Nov 24
Fall sowing Oct 27 – Nov 17
Fall sowing Oct 13 – Oct 27
Sow or transplant Dec 10 – Dec 24
Fall sowing Oct 13 – Nov 10
Transplant Dec 24 – Jan 7
Fall sowing Sep 29 – Oct 13
Transplant Dec 17 – Dec 31
Fall sowing Sep 29 – Oct 13
Fall sowing Sep 29 – Oct 13
Fall sowing Nov 10 – Dec 1
Fall sowing Oct 13 – Oct 27
Plant Dec 10 – Dec 24
Based on the average last frost (Jan 7) and first frost (Dec 22). The dashed lines mark those dates. Seed packets list days to maturity; adjust for your varieties.