Marin County, in California, sits in USDA hardiness zone 9b — room for a real mix of vegetables, fruit, and perennials matched to the local frost calendar.
The conditions favor okra, meyer lemon, california poppy, and artichoke, among others — though every individual site edits that list with its own soil, sun, and drainage.
Marin County lies within the San Francisco Bay Area — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Marin County holds more than one microclimate.
Soils and elevations shift across Marin County, so your frost dates and drainage aren't the county average. 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 Marin County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Marin County — the short answer
Marin County, California: USDA zone 9b, about 336 days between hard freezes, across 333K acres.
- USDA zone
- 9b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Jan 9
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Dec 11
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~336
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 333K acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are county 28°F normals: light frosts run a few weeks past them, and tender transplants usually wait 2–3 weeks after the last hard freeze.
Hardiness Zone Range
Zone 9b is Marin County's average, not your lot's — a low corner or a tree line moves it. Against Marin County's 336-day season, see what your own ground reads.
Heat and winter chill in Marin County
Across a year, Marin County accumulates about 2,769 growing degree days above 50°F, about 988 fewer than the middle California county — ahead of 15 of California’s 57 counties. Degree days are the heat a crop actually gets to work with — more of them is more room to ripen a long-season crop before the freeze closes the window.
Winter banks about 854 hours below 45°F, 333 fewer than the California middle of 1,187. Chill is what tells a fruit tree its dormancy is over, and it is set by climate rather than by anything you can build.
Grounded in PRISM Climate Group, Oregon State University — 1991–2020 monthly normals
Soil in Marin County
Across Marin County, the ground is predominantly Mollisols, where Tocaloma, Saurin, and Tomales are the most extensive named soil series. The soil is generally well drained with a loam surface. Topsoil pH runs about 6.1–6.3, slightly acidic. Rainfall drains through hydrologic group D soils.
Soil order
Mollisols
Drainage
Well drained
Hydric soils
9%
Soil still varies lot by lot — soil types explained.
How the ground varies across Marin County
The USDA soil survey maps 50% of Marin County as well drained — but another 28% drains differently: 14% moderately well drained, 6% somewhat poorly drained.
Tocaloma is the most extensive named soil at 13% of mapped acres, then Saurin (8%) and Tomales (7%).
Which of them your own lot sits on is a parcel question, not a county one. Check your address for the survey at your boundary.
What this means for growing in Marin County
Each reading below is measured for Marin County itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Drainage
MeasuredThe dominant soils across Marin County are well drained, in hydrologic group D — ground that drains quickly.
The upside is soil you can work early in spring and roots that never drown; the cost is that fast-draining ground dries out fast and leaches nutrients away before plants can use them.
Work in compost and mulch to hold moisture and feed, and water more often in short doses than deep and rarely.
USDA NRCS SSURGO
Surface pH
MeasuredTopsoil across Marin County runs about pH 6.1–6.3, close to neutral.
This is the range most vegetables prefer — one correction you probably do not have to make, which is genuinely good news for a new bed.
Keep it there with compost rather than lime or sulfur, and only amend if your own soil test says otherwise.
USDA NRCS SSURGO
Season length
MeasuredMarin County runs about 336 days between hard freezes — 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
MeasuredMarin County 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 Marin County is in
Marin County spans 2 EPA Level III ecoregions — Central California Foothills and Coastal Mountains (71%) and Coast Range (29%). Which one your land falls in changes what grows wild there and how the ground behaves, and a county-wide answer cannot tell you which.
What Grows in Marin County
We scored all 1,086 plants against Marin County's own USDA zone 9b and its own 336-day season between hard freezes, using the same matching engine that runs a full parcel report. These cleared both. Sun, soil pH and drainage vary lot by lot — those are the parcel questions below. Each card opens that plant's California profile.
Is it too late to plant in Marin County?
Rarely: the season closes in stages, not all at once, and each stage has its crops. 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. And with a calendar this mild, the honest answer is that planting barely stops — winter opens seasons colder regions never see.
Documented around Marin County
- monarch butterfly150 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Marin County
USGS estimates 98 lb of 2,4-d on Marin County farmland in 2019, its largest by weight, ahead of Glyphosate (47 lb) and Boscalid (26 lb).
Farmland across the whole county, not any one lot. Check your address for the site-by-site record.
Safe to Grow Here?
What the federal record shows across Marin County — and how to grow with it.
We checked the federal record across Marin County — 1,673 documented sites across 7 of the 9 source types we track.
The most significant on record: 8 Superfund sites (none NPL-listed). Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
There's a meaningful federal record across Marin County — worth a look before you plant food, not a reason to hold back from growing. Proximity to a documented site is information, not a diagnosis of any one yard. A soil test before new food beds is the sensible precaution here, and the map shows exactly which sites sit where, so you can see what's actually near you.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Marin County
Closest first, across Marin County. Listing isn't leaking, and distance isn't exposure.
- ClaimsMining · 2.0 mi
- CALIFORNIA STATE PARKS SAMUEL P TAYLOR SPBrownfields · 2.2 mi
- VEDANTA SOCIETY OF NORTHERN CALIFORNIABrownfields · 2.3 mi
- PACIFIC GAS & ELECTRIC CORPBrownfields · 2.3 mi
- PG&EBrownfields · 2.3 mi
- NICASIO ROCK QUARRYBrownfields · 2.6 mi
- CITY OF SAN RAFAEL-FIRE DEPTBrownfields · 2.7 mi
- CALTRANS, DISTRICT 4 EA 4H8704Brownfields · 3.0 mi
- POINT REYES MAINTENANCE STNBrownfields · 3.0 mi
- CHEDA'S GARAGEBrownfields · 3.4 mi
- PACIFIC BELLBrownfields · 3.4 mi
- POINT REYES COMMUNITY HEALTH CENTER PHARMACYBrownfields · 3.5 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Marin County'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 Marin County.
Total Sites
1,673
across Marin County
Risk Level
Elevated
Highest-severity
8 Superfund sites (none NPL-listed)
Sources Checked
across Marin County
Severity Distribution
across Marin County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Marin County, Brownfields runs higher than the national average — 1,539 sites across Marin County. 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 Marin County
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 Marin County average
Your land is one point inside Marin County
Everything above resolves to Marin County as a whole — one PHZM band and one county frost record, read across 333K acres. 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 county 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 county average.
Your Lot vs the Marin County Average
Marin County Average
- ●USDA Zones 9b, averaged across Marin County
- ●One soil character for all of Marin County
- ●Frost dates read at Marin County's scale: Jan 9 to Dec 11
YOUR Parcel
- ✓Your exact zone, not Marin County's 9b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Marin County
Pull a site-specific report for your exact address in Marin County, California — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Marin County averages can't show:
We read public map data around Marin County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Marin County average
How we know this about Marin County
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at county grain; hard-freeze dates from NOAA 1991–2020 28°F normals at this county’s own record where one resolves, and the labelled statewide window where none does; soils from the USDA NRCS SSURGO survey, area-weighted across the county’s own map units; boundaries and acreage from US Census TIGER/Line 2025; the contamination and pesticide records from the federal sources named in their beats above. Where Marin County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Marin County
When does frost risk typically end in Marin County?
The last hard freeze (28°F) in Marin County 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.
How long is the growing season in Marin County?
Measured between 28°F hard freezes, Marin County 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 Marin County?
The federal record around Marin County is a meaningful one — 1,673 documented sites, mostly Brownfields entries (1,539), the nearest Mining record about 2.0 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.
Everything above is measured at Marin County's scale — its 9b band and its 336-day season. Your yard writes its own version of Marin County's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
Will It Grow Here?
Zone fit is the first question — each answer below reads California's frost window, season length, and soil profile against the plant's real requirements.
What this page reads at Marin County’s own scale
9 of the readings below were taken at Marin County's own scale — its own ~336-day span between 28°F freezes, the 3 most extensive soil series mapped here and 1,673 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Marin County's own USDA hardiness band, zones 9bUSDA PHZM 2023
- Marin County's own 28°F hard-freeze dates and its ~336-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Marin CountyUSDA NRCS SSURGO
- 1,673 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Mining record about 2.0 miles outFederal environmental registers
- Marin County's boundary and the 332,890 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 9b and a ~336-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions Marin County spans, Central California Foothills and Coastal Mountains the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Marin County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Marin County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every California grower plans around — written at state scale, so they stay on the state guidefrom California
What this page can’t tell you
- How the season shifts across Marin County — the ~336 days above is one reading at its centre; the 12 towns below each carry their owntowns in this county →
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Marin County's 332,890 acreswhy one lot differs from the next →
- Which of those 1,673 documented sites actually reaches your soil — that needs your address, the wind, and the groundwater directionhow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — none of it survives being averaged over Marin Countyread your own land →