Castro Valley, California, sits in USDA hardiness zone 9b — a zone band wide enough that plant choice, not possibility, is the interesting question.
Among the crops suited to this profile: okra, meyer lemon, california poppy, and artichoke. The site-level story — soil, sun, drainage — decides the rest.
Even in Castro Valley, 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 Castro Valley 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 Castro Valley — soil, climate, flood, and parcel records. How we handle your address.
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Castro Valley — the short answer
Castro Valley, California: USDA zone 9b, about 334 days between hard freezes, across 11K acres of town.
- 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
- Town area
- 11K 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 Castro Valley's average, not your lot's — a low corner or a tree line moves it. Against Castro Valley's 334-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Castro Valley
Each reading below is measured for Castro Valley itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
From county recordsCastro Valley runs about 334 days between hard freezes (read from Alameda County, the closest normal to Castro Valley) — 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
MeasuredCastro Valley 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 Castro Valley is in
Castro Valley sits in the Central California Foothills and Coastal Mountains — EPA Level III, inside the wider Mediterranean California. That is read at Castro Valley's own centroid rather than borrowed from Alameda County.
What Grows in Castro Valley
Every plant below cleared Castro Valley'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 Castro Valley?
Too late for some crops, right on time for others — a growing season is a sequence, not a deadline. 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. And with a calendar this mild, the honest answer is that planting barely stops — winter opens seasons colder regions never see.
Documented around Castro Valley
Spotted lanternfly documented 10 miles from Castro Valley, first recorded 2023. What to watch for.
What's on the federal record near Castro Valley
Closest first, within ~10 miles of Castro Valley. Listing isn't leaking, and distance isn't exposure.
- MEGAN HORNBECKERBrownfields · 800 ft
- BILL GUMINABrownfields · 900 ft
- ROBERT TAYLORBrownfields · 1400 ft
- CANTERBERRY, MARTIEBrownfields · 1500 ft
- KEISKE SATAKABrownfields · 1900 ft
- SEGOTTA TRUCKING INCBrownfields · 2400 ft
- AUTO ANALYSTS IIBrownfields · 0.5 mi
- JOHN HARRINGTONBrownfields · 0.5 mi
- CREEKSIDE MIDDLE SCHOOLBrownfields · 0.6 mi
- REDWOOD CHAPEL COMMUNITY CHURCHBrownfields · 0.6 mi
- KODY BLANCHERBrownfields · 0.6 mi
- S K SPECIALTIESBrownfields · 0.7 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Castro Valley'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 Castro Valley.
Total Sites
5,214
within ~10 miles of Castro Valley
Risk Level
Elevated
Highest-severity
19 Superfund sites (none NPL-listed)
Sources Checked
within ~10 miles of Castro Valley
Severity Distribution
within ~10 miles of Castro Valley
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Castro Valley, Brownfields runs higher than the national average — 4,519 sites within ~10 miles of Castro Valley. 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 Castro Valley
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 Castro Valley average
Your land is one point inside Castro Valley
Everything above resolves to Castro Valley as a whole — one PHZM band, read across 11K acres, with hard-freeze dates borrowed from Alameda County’s record because no 30-year normal resolves at this town’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 town 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 Castro Valley Average
Castro Valley Average
- ●USDA Zones 9b, averaged across Castro Valley
- ●One soil character for all of Castro Valley
- ●Frost dates read at Castro Valley's scale: Jan 12 to Dec 12
YOUR Parcel
- ✓Your exact zone, not Castro Valley's 9b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Castro Valley
Pull a site-specific report for your exact address in Castro Valley, California — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Castro Valley averages can't show:
We read public map data around Castro Valley — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Castro Valley average
How we know this about Castro Valley
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this town’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 town grain anywhere on this page — there is no town-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 Castro Valley
When does frost risk typically end in Castro Valley?
The last hard freeze (28°F) in Castro Valley 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 Castro Valley?
The first hard freeze (28°F) in Castro Valley 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 Castro Valley?
Measured between 28°F hard freezes, Castro Valley 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 Castro Valley?
The federal record around Castro Valley is a meaningful one — 5,214 documented sites, mostly Brownfields entries (4,519), the nearest Brownfields record about 0.2 miles 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 Castro Valley?
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 Castro Valley's scale — its 9b band and its 334-day season. Your yard writes its own version of Castro Valley'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 Castro Valley’s own scale
6 of the readings below were taken at Castro Valley's own scale — the 10,783 acres it covers and 5,214 documented sites around it; 5 are borrowed from a wider read, named and linked below.
Measured here
- Castro Valley's own USDA hardiness band, zones 9bUSDA PHZM 2023
- 5,214 documented contamination sites on the federal record near Castro Valley, the closest Brownfields record about 0.2 miles out from the town centreFederal environmental registers
- Castro Valley's boundary and the 10,783 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 Castro Valley's own centroid, the Central California Foothills and Coastal MountainsUS EPA Level III Ecoregions
- A documented spotted-lanternfly record within reach of Castro Valleylydemapr (De Bona & Helmus), 10 km survey lattice
Inherited from a wider read
- The 28°F hard-freeze dates — Castro Valley 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 Castro Valley's 10,783 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 Castro Valley's 10,783 acreswhy one lot differs from the next →
- Which side of Castro Valley you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 10,783 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Brownfields record about 0.2 miles 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 Castro Valley-wide figureread your own land →