Union City, California, sits in USDA hardiness zone 9b — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
Reliable performers under these conditions include okra, meyer lemon, california poppy, and artichoke; what your own ground favors still comes down to its soil, sun, and drainage.
Even in Union City, no two yards are alike.
A low spot, a south-facing slope, or a stand of trees moves the frost date and sun across a single Union City lot. Enter your address and we'll score 1,086 plants against your land's actual soil, sun, and frost.
We read public map data around Union City — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Union City — the short answer
Union City, California: USDA zone 9b, about 334 days between hard freezes, across 12K acres of city.
- USDA zone
- 9b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Jan 12
- Alameda County normal — NOAA 1991–2020, nearest to this town
- First hard freeze (28°F)
- Dec 12
- Alameda County normal — NOAA 1991–2020, nearest to this town
- Days between freezes
- ~334
- Alameda County normal — NOAA 1991–2020, nearest to this town
- City area
- 12K acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. No 30-year normal resolves at this town’s own centroid, so the hard-freeze dates are Alameda County’s — the closest measured record, labelled as such rather than passed off as local.
Hardiness Zone Range
Zone 9b is Union City's average, not your lot's — a low corner or a tree line moves it. Against Union City's 334-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Union City
Each reading below is measured for Union City itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
From county recordsUnion City runs about 334 days between hard freezes (read from Alameda County, the closest normal to Union City) — close to year-round growing.
Frost is rarely the limit here; winter plantings are as real as summer ones, and the harder question is which crops shrug off the summer heat.
Grow cool-season crops through the mild winter, and choose heat-tolerant varieties for the summer beds.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredUnion City sits in USDA hardiness zone 9b.
The zone sets which perennials, shrubs, and fruit trees live through an average winter here — a plant rated for a colder zone is a safe bet, one rated warmer needs winter protection or gets treated as an annual.
Match perennials and fruit to the zone before you buy, so nothing you plant is a gamble against the cold.
USDA PHZM 2023
The kind of country Union City is in
Union City sits in the Central California Foothills and Coastal Mountains — EPA Level III, inside the wider Mediterranean California. That is read at Union City's own centroid rather than borrowed from Alameda County.
What Grows in Union City
Every plant below cleared Union City's own zone 9b and its 334-day season. Each card opens that plant's California profile. How we score.
Is it too late to plant in Union City?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Jan 1; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Jan 12 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Dec 12 — long-season crops need about 90 days of runway, quick greens only 30. With almost year-round growing weather, timing is about heat and rainfall more than frost — some bench is always in play.
Documented around Union City
Spotted lanternfly documented 16 miles from Union City, first recorded 2023. What to watch for.
What's on the federal record near Union City
Closest first, within ~10 miles of Union City. Listing isn't leaking, and distance isn't exposure.
- AT&T California - P5006Underground Storage Tanks · 500 ft
- PACIFIC BELLBrownfields · 600 ft
- Mission Shell GasolineUnderground Storage Tanks · 1100 ft
- UNION AUTO REPAIRBrownfields · 1100 ft
- SERVICE STATION - SAP 136200Brownfields · 1200 ft
- CALTRANS D-4 3G7104Brownfields · 1500 ft
- GILBERT CASTILLONBrownfields · 1700 ft
- UNION CITY INDUSTRIAL PARKBrownfields · 2100 ft
- STM INCBrownfields · 2100 ft
- MCKESSON CHEMICAL COMPANYBrownfields · 2100 ft
- AIRGAS USA, LLCBrownfields · 2200 ft
- TIBURCIO VASQUEZ HEALTH CENTER INCBrownfields · 2200 ft
6 more sites are on the record inside the same radius. See them on the map
Measured from Union City's center, not your beds. Run your own address for what's upwind of you specifically.
Environmental Intelligence
The counts behind that headline — every source type on the record near Union City.
Total Sites
5,117
within ~10 miles of Union City
Risk Level
Elevated
Highest-severity
10 Superfund sites (none NPL-listed)
Sources Checked
within ~10 miles of Union City
Severity Distribution
within ~10 miles of Union City
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Union City, Brownfields runs higher than the national average — 4,403 sites within ~10 miles of Union City. Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
Brownfields: Brownfield sites are former commercial or industrial properties where legacy soil contamination (heavy metals, PAHs, petroleum compounds) may persist.
Check EPA brownfield remediation status — many sites have completed cleanup with institutional controls.
Check your specific parcel in Union City
Get exact proximity distances to contamination sources for your specific parcel — plus soil, sun, drainage, and 1,086 plant recommendations.
25+ data sources read at your address, not the Union City average
Your land is one point inside Union City
Everything above resolves to Union City as a whole — one PHZM band, read across 12K acres, with hard-freeze dates borrowed from Alameda County’s record because no 30-year normal resolves at this city’s own centroid. Your parcel is one point inside that footprint. Slope, tree cover, a low spot that pools cold air, and what is in the soil are all resolved at the address, and none of them are visible at city scale. That is the honest boundary of this page, and the reason the next step is a reading of your own ground rather than a better local average.
Your Lot vs the Union City Average
Union City Average
- ●USDA Zones 9b, averaged across Union City
- ●One soil character for all of Union City
- ●Frost dates read at Union City's scale: Jan 12 to Dec 12
YOUR Parcel
- ✓Your exact zone, not Union City's 9b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Union City
Pull a site-specific report for your exact address in Union City, California — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Union City averages can't show:
We read public map data around Union City — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Union City average
How we know this about Union City
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this city’s own centroid; hard-freeze dates from NOAA 1991–2020 28°F normals at Alameda County’s record, because none resolves here; boundaries and acreage from US Census TIGER/Line 2025; the contamination records from the federal sources named in their beats above. Soil is not read at city grain anywhere on this page — there is no city-resolution survey in our data, which is why you will find no soil grid here rather than a statewide one wearing a local label. The resolution ledger below names every figure this page inherited.
Common questions about Union City
When does frost risk typically end in Union City?
The last hard freeze (28°F) in Union City typically lands around Jan 12, per NOAA 1991–2020 climate normals — earlier than the light-frost dates most charts quote. That marks the hard freeze, not the last light frost — lighter frosts keep biting past it, which is why tender transplants here wait until about Feb 2.
When is the first frost in Union City?
The first hard freeze (28°F) in Union City typically arrives around Dec 12, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Nov 28, so the watching starts about Nov 12 — about 334 days after the spring freeze cleared.
How long is the growing season in Union City?
Measured between 28°F hard freezes, Union City sees about 334 frost-free days — roughly Jan 12 through Dec 12, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Feb 2 to Nov 28, about 299 days.
Is the soil safe to grow vegetables in Union City?
The federal record around Union City is a meaningful one — 5,117 documented sites, mostly Brownfields entries (4,403), the nearest Underground Storage Tanks record under a tenth of a mile out — so a soil test before new food beds is a sensible precaution here, not a reason to hold back from growing. Remember that proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what sits where.
How do I protect my plants from frost in Union City?
From about Nov 12 the job here turns from planting to protecting — the last start even a 30-day crop can finish. As the season closes around the first 28°F hard freeze near Dec 12 (NOAA 1991–2020 climate normals), three moves buy time: row cover or an old sheet over tender plants on still, clear nights; water the soil the afternoon before a freeze, so it holds warmth overnight; and harvest tomatoes, peppers and basil before Dec 12. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Union City's scale — its 9b band and its 334-day season. Your yard writes its own version of Union City's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
What this page reads at Union City’s own scale
6 of the readings below were taken at Union City's own scale — the 12,415 acres it covers and 5,117 documented sites around it; 5 are borrowed from a wider read, named and linked below.
Measured here
- Union City's own USDA hardiness band, zones 9bUSDA PHZM 2023
- 5,117 documented contamination sites on the federal record near Union City, the closest Underground Storage Tanks record under a tenth of a mile out from the town centreFederal environmental registers
- Union City's boundary and the 12,415 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 9b and a ~334-day seasonGrowable Ground crop-matching engine
- The ecoregion at Union City's own centroid, the Central California Foothills and Coastal MountainsUS EPA Level III Ecoregions
- A documented spotted-lanternfly record within reach of Union Citylydemapr (De Bona & Helmus), 10 km survey lattice
Inherited from a wider read
- The 28°F hard-freeze dates — Union City has no normal of its own, so its county's is the closest measured readfrom Alameda County
- Soil character — no town-scale survey exists, so Union City's 12,415 acres read through its county's SSURGO summaryfrom Alameda County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Alameda County
- The growing challenges every California grower plans around — written at state scale, so they stay on the state guidefrom California
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Alameda County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Union City's 12,415 acreswhy one lot differs from the next →
- Which side of Union City you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 12,415 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks record under a tenth of a mile out, measured from the town centrehow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — measured at your address, and averaged away by any Union City-wide figureread your own land →