Alum Rock, California, sits in USDA hardiness zone 9b — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
Expect okra, meyer lemon, california poppy, and artichoke to be strong candidates here; the deciding factors on any one parcel stay local — soil, sun, and drainage.
Even in Alum Rock, 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 Alum Rock 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 Alum Rock — soil, climate, flood, and parcel records. How we handle your address.
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Alum Rock — the short answer
Alum Rock, California: USDA zone 9b, about 331 days between hard freezes, across 556 acres of town.
- USDA zone
- 9b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Jan 17
- Santa Clara County normal — NOAA 1991–2020, nearest to this town
- First hard freeze (28°F)
- Dec 14
- Santa Clara County normal — NOAA 1991–2020, nearest to this town
- Days between freezes
- ~331
- Santa Clara County normal — NOAA 1991–2020, nearest to this town
- Town area
- 556 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 Santa Clara County’s — the closest measured record, labelled as such rather than passed off as local.
Hardiness Zone Range
Zone 9b is Alum Rock's average, not your lot's — a low corner or a tree line moves it. Against Alum Rock's 331-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Alum Rock
Each reading below is measured for Alum Rock itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
From county recordsAlum Rock runs about 331 days between hard freezes (read from Santa Clara County, the closest normal to Alum Rock) — 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
MeasuredAlum Rock 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 Alum Rock is in
Alum Rock sits in the Central California Foothills and Coastal Mountains — EPA Level III, inside the wider Mediterranean California. That is read at Alum Rock's own centroid rather than borrowed from Santa Clara County.
What Grows in Alum Rock
Every plant below cleared Alum Rock's own zone 9b and its 331-day season. Each card opens that plant's California profile. How we score.
Is it too late to plant in Alum Rock?
Usually not — gardeners here simply switch what goes in the ground as the season moves. 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 17 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Dec 14 — 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.
What's on the federal record near Alum Rock
Closest first, within ~10 miles of Alum Rock. Listing isn't leaking, and distance isn't exposure.
- LUZANA BRIGNON DDSBrownfields · 450 ft
- JAMES HIGGINS DDSBrownfields · 450 ft
- ROYAL DRY CLEANINGBrownfields · 1400 ft
- KAL INVESTMENT LLCBrownfields · 1500 ft
- PLANNED PARENTHOOD MAR MONTEBrownfields · 1500 ft
- SAN JOSE JOB CORPS CENTERBrownfields · 1800 ft
- EAST SIDE UHSD-JAMES LICK HSBrownfields · 1800 ft
- SJWC FLEMING AVEBrownfields · 1800 ft
- WHITE ROAD AUTO SERVICEBrownfields · 2000 ft
- CAL GAS MINI MARTBrownfields · 2000 ft
- CAL GAS & DIESELUnderground Storage Tanks · 2000 ft
- PACIFIC BELLBrownfields · 2200 ft
6 more sites are on the record inside the same radius. See them on the map
Measured from Alum Rock'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 Alum Rock.
Sources Checked
within ~10 miles of Alum Rock
Severity Distribution
within ~10 miles of Alum Rock
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Alum Rock, Brownfields runs higher than the national average — 6,812 sites within ~10 miles of Alum Rock. It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
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 Alum Rock
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 Alum Rock average
Your land is one point inside Alum Rock
Everything above resolves to Alum Rock as a whole — one PHZM band, read across 556 acres, with hard-freeze dates borrowed from Santa Clara 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 Alum Rock Average
Alum Rock Average
- ●USDA Zones 9b, averaged across Alum Rock
- ●One soil character for all of Alum Rock
- ●Frost dates read at Alum Rock's scale: Jan 17 to Dec 14
YOUR Parcel
- ✓Your exact zone, not Alum Rock's 9b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Alum Rock
Pull a site-specific report for your exact address in Alum Rock, California — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Alum Rock averages can't show:
We read public map data around Alum Rock — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Alum Rock average
How we know this about Alum Rock
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 Santa Clara 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 Alum Rock
When does frost risk typically end in Alum Rock?
The last hard freeze (28°F) in Alum Rock typically lands around Jan 17, 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 7.
When is the first frost in Alum Rock?
The first hard freeze (28°F) in Alum Rock typically arrives around Dec 14, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Nov 30, so the watching starts about Nov 14 — about 331 days after the spring freeze cleared.
How long is the growing season in Alum Rock?
Measured between 28°F hard freezes, Alum Rock sees about 331 frost-free days — roughly Jan 17 through Dec 14, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Feb 7 to Nov 30, about 296 days.
Is the soil safe to grow vegetables in Alum Rock?
The federal record around Alum Rock runs heavier than most — 7,659 documented sites, mostly Brownfields entries (6,812), the nearest Brownfields record under a tenth of a mile out — so test the soil before planting food in the ground, and raised beds with clean imported soil grow well in the meantime. Even here, proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what's recorded and where.
How do I protect my plants from frost in Alum Rock?
From about Nov 14 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 14 (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 14. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Alum Rock's scale — its 9b band and its 331-day season. Your yard writes its own version of Alum Rock'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 Alum Rock’s own scale
5 of the readings below were taken at Alum Rock's own scale — the 556 acres it covers and 7,659 documented sites around it; 5 are borrowed from a wider read, named and linked below.
Measured here
- Alum Rock's own USDA hardiness band, zones 9bUSDA PHZM 2023
- 7,659 documented contamination sites on the federal record near Alum Rock, the closest Brownfields record under a tenth of a mile out from the town centreFederal environmental registers
- Alum Rock's boundary and the 556 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 9b and a ~331-day seasonGrowable Ground crop-matching engine
- The ecoregion at Alum Rock's own centroid, the Central California Foothills and Coastal MountainsUS EPA Level III Ecoregions
Inherited from a wider read
- The 28°F hard-freeze dates — Alum Rock has no normal of its own, so its county's is the closest measured readfrom Santa Clara County
- Soil character — no town-scale survey exists, so Alum Rock's 556 acres read through its county's SSURGO summaryfrom Santa Clara County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Santa Clara 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 Santa Clara County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Alum Rock's 556 acreswhy one lot differs from the next →
- Which side of Alum Rock you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 556 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Brownfields 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 Alum Rock-wide figureread your own land →
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