San Geronimo, California, sits in USDA hardiness zone 9b — enough range to grow cool-season vegetables, hardy fruit, and warm-season crops that mature before the first hard frost.
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 San Geronimo, 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 San Geronimo 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 San Geronimo — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
San Geronimo — the short answer
San Geronimo, California: USDA zone 9b, about 336 days between hard freezes, across 965 acres of town.
- USDA zone
- 9b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Jan 9
- Marin County normal — NOAA 1991–2020, nearest to this town
- First hard freeze (28°F)
- Dec 11
- Marin County normal — NOAA 1991–2020, nearest to this town
- Days between freezes
- ~336
- Marin County normal — NOAA 1991–2020, nearest to this town
- Town area
- 965 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 Marin County’s — the closest measured record, labelled as such rather than passed off as local.
Hardiness Zone Range
Zone 9b is San Geronimo's average, not your lot's — a low corner or a tree line moves it. Against San Geronimo's 336-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in San Geronimo
Each reading below is measured for San Geronimo itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
From county recordsSan Geronimo runs about 336 days between hard freezes (read from Marin County, the closest normal to San Geronimo) — 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
MeasuredSan Geronimo 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 San Geronimo is in
San Geronimo sits in the Coast Range — EPA Level III, inside the wider Marine West Coast Forest. That is read at San Geronimo's own centroid, and it is not what its county reads: Marin County is mostly Central California Foothills and Coastal Mountains. The wider page above you is answering a different question about different ground.
What Grows in San Geronimo
Every plant below cleared San Geronimo's own zone 9b and its 336-day season. Each card opens that plant's California profile. How we score.
Is it too late to plant in San Geronimo?
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 9 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Dec 11 — long-season crops need about 90 days of runway, quick greens only 30. In a climate this gentle, “too late” hardly applies — the question becomes which crops prefer the cooler months ahead.
Documented around San Geronimo
Spotted lanternfly documented 29 miles from San Geronimo, first recorded 2023. What to watch for.
What's on the federal record near San Geronimo
Closest first, within ~10 miles of San Geronimo. Listing isn't leaking, and distance isn't exposure.
- SAN GERONIMO GOLF COURSEBrownfields · 0.6 mi
- PACIFIC BELLBrownfields · 0.7 mi
- MARIN MUNICIPAL WATER DISTRICTBrownfields · 0.9 mi
- Maillard RanchMining · 1.5 mi
- CITY OF SAN RAFAEL-FIRE DEPARMENTBrownfields · 1.5 mi
- JEREMY GAUNTBrownfields · 1.5 mi
- SERENITY KNOLLS TREATMENT CENTER ACADIA HEALTHCAREBrownfields · 1.8 mi
- CHRISTIAN JENSENBrownfields · 2.5 mi
- GIRL SCOUTS OF NORTHERN CALIFORNIABrownfields · 2.5 mi
- NERVIANI PAVING INCBrownfields · 2.7 mi
- JOE CASTAINGBrownfields · 3.3 mi
- JAKE MILLERBrownfields · 3.3 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from San Geronimo'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 San Geronimo.
Total Sites
1,331
within ~10 miles of San Geronimo
Risk Level
Elevated
Highest-severity
5 Superfund sites (none NPL-listed)
Sources Checked
within ~10 miles of San Geronimo
Severity Distribution
within ~10 miles of San Geronimo
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around San Geronimo, Brownfields runs higher than the national average — 1,240 sites within ~10 miles of San Geronimo. That's not a problem with your land — it's information about 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 San Geronimo
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 San Geronimo average
Your land is one point inside San Geronimo
Everything above resolves to San Geronimo as a whole — one PHZM band, read across 965 acres, with hard-freeze dates borrowed from Marin 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 San Geronimo Average
San Geronimo Average
- ●USDA Zones 9b, averaged across San Geronimo
- ●One soil character for all of San Geronimo
- ●Frost dates read at San Geronimo's scale: Jan 9 to Dec 11
YOUR Parcel
- ✓Your exact zone, not San Geronimo's 9b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in San Geronimo
Pull a site-specific report for your exact address in San Geronimo, California — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that San Geronimo averages can't show:
We read public map data around San Geronimo — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the San Geronimo average
How we know this about San Geronimo
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 Marin 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 San Geronimo
When does frost risk typically end in San Geronimo?
The last hard freeze (28°F) in San Geronimo typically lands around Jan 9, 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 Jan 30.
When is the first frost in San Geronimo?
The first hard freeze (28°F) in San Geronimo typically arrives around Dec 11, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Nov 27, so the watching starts about Nov 11 — about 336 days after the spring freeze cleared.
How long is the growing season in San Geronimo?
Measured between 28°F hard freezes, San Geronimo sees about 336 frost-free days — roughly Jan 9 through Dec 11, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jan 30 to Nov 27, about 301 days.
Is the soil safe to grow vegetables in San Geronimo?
The federal record around San Geronimo is a meaningful one — 1,331 documented sites, mostly Brownfields entries (1,240), the nearest Brownfields record about 0.6 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 San Geronimo?
From about Nov 11 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 11 (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 11. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at San Geronimo's scale — its 9b band and its 336-day season. Your yard writes its own version of San Geronimo'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 San Geronimo’s own scale
6 of the readings below were taken at San Geronimo's own scale — the 965 acres it covers and 1,331 documented sites around it; 5 are borrowed from a wider read, named and linked below.
Measured here
- San Geronimo's own USDA hardiness band, zones 9bUSDA PHZM 2023
- 1,331 documented contamination sites on the federal record near San Geronimo, the closest Brownfields record about 0.6 miles out from the town centreFederal environmental registers
- San Geronimo's boundary and the 965 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 9b and a ~336-day seasonGrowable Ground crop-matching engine
- San Geronimo sits in the Coast Range — not the ecoregion its county mostly readsUS EPA Level III Ecoregions
- A documented spotted-lanternfly record within reach of San Geronimolydemapr (De Bona & Helmus), 10 km survey lattice
Inherited from a wider read
- The 28°F hard-freeze dates — San Geronimo has no normal of its own, so its county's is the closest measured readfrom Marin County
- Soil character — no town-scale survey exists, so San Geronimo's 965 acres read through its county's SSURGO summaryfrom Marin County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Marin 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 Marin County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among San Geronimo's 965 acreswhy one lot differs from the next →
- Which side of San Geronimo you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 965 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Brownfields record about 0.6 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 San Geronimo-wide figureread your own land →