San Mateo County, in California, sits in USDA hardiness zone 10a — a zone band wide enough that plant choice, not possibility, is the interesting question.
Well-matched crops include artichoke, meyer lemon, california poppy, and cabbage, and the gap between "grows in the area" and "grows in your yard" is closed by soil, sun, and drainage.
San Mateo County lies within the San Francisco Bay Area and the Pacific Northwest — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring
San Mateo County holds more than one microclimate.
Soils and elevations shift across San Mateo 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 San Mateo County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
San Mateo County — the short answer
San Mateo County, California: USDA zone 10a, no 28°F killing freeze on record — the season is year-round, across 287K acres.
- USDA zone
- 10a
- USDA PHZM 2023
- Killing freeze
- None on record
- NOAA RCC ACIS 1991–2020, county record
- County area
- 287K acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. The year-round finding is measured — a 30-year record with no 28°F killing freeze in it — never inferred from missing dates.
Hardiness Zone Range
Zone 10a is San Mateo County's average, not your lot's — a low corner or a tree line moves it. Against San Mateo County's no killing freeze on record, see what your own ground reads.
Heat and winter chill in San Mateo County
Across a year, San Mateo County accumulates about 2,419 growing degree days above 50°F, about 1,338 fewer than the middle California county — ahead of 11 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 721 hours below 45°F, 466 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 San Mateo County
Across San Mateo County, the ground is predominantly Mollisols, where Hugo, Josephine, and Lobitos 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
4%
Soil still varies lot by lot — soil types explained.
How the ground varies across San Mateo County
The USDA soil survey maps 50% of San Mateo County as well drained — but another 12% drains differently: 5% moderately well drained, 3% excessively drained.
Hugo is the most extensive named soil at 9% of mapped acres, then Josephine (7%) and Lobitos (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 San Mateo County
Each reading below is measured for San Mateo 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 San Mateo 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 San Mateo 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
MeasuredSan Mateo County records no 28°F killing freeze at all across the 30-year station record — 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 Mateo County sits in USDA hardiness zone 10a.
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 Mateo County is in
San Mateo County spans 2 EPA Level III ecoregions — Coast Range (66%) and Central California Foothills and Coastal Mountains (34%). 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 San Mateo County
We scored all 1,086 plants against San Mateo County's own USDA zone 10a and its own 365-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.
Documented around San Mateo County
Spotted lanternfly documented 24 miles from San Mateo County, first recorded 2023. What to watch for.
- monarch butterfly56 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in San Mateo County
USGS estimates 771 lb of Triclopyr on San Mateo County farmland in 2019, its largest by weight, ahead of Glyphosate (558 lb) and 2,4-d (151 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 San Mateo County — and how to grow with it.
We checked the federal record across San Mateo County — 5,427 documented sites across 7 of the 9 source types we track.
The most significant on record: 16 Superfund sites (none NPL-listed). Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
San Mateo County carries one of the heavier federal records we track — and that's not a verdict on your yard. Proximity to a documented site is information, not a diagnosis: nothing here says any particular parcel is affected. It does earn one concrete step — before food beds go in the ground, a professional soil test tells you exactly what you're working with, and raised beds with clean imported soil grow well almost anywhere in the meantime.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near San Mateo County
Closest first, across San Mateo County. Listing isn't leaking, and distance isn't exposure.
- CALTRANS DIST 4Brownfields · 2.6 mi
- DBA AZEVEDO FEED (WILBUR J AZEVEDO)Brownfields · 2.8 mi
- HALF MOON BAY GRADING & PAVING INCBrownfields · 2.9 mi
- 006S005W27Q001MNitrate · 2.9 mi
- GIUSTI FARM LLCBrownfields · 3.1 mi
- BOB NUTTING PAINTINGBrownfields · 3.1 mi
- CABRILLO FARMS AGRICULTURE INC.Brownfields · 3.2 mi
- BAY CITY FLOWER COMPANY INCBrownfields · 3.3 mi
- COASTSIDE COUNTY WATER DISTRICTPFAS · 3.5 mi
- CALTRANS DISTRICT 4, P.N. 00-0000-0812Brownfields · 3.5 mi
- RICE TRUCKING-SOIL FARMBrownfields · 3.6 mi
- PARROT ENVIRO PRO TECHBrownfields · 3.7 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from San Mateo 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 San Mateo County.
Total Sites
5,427
across San Mateo County
Risk Level
High
Highest-severity
16 Superfund sites (none NPL-listed)
Sources Checked
across San Mateo County
Severity Distribution
across San Mateo County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around San Mateo County, Brownfields runs higher than the national average — 4,961 sites across San Mateo 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 San Mateo 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 San Mateo County average
Your land is one point inside San Mateo County
Everything above resolves to San Mateo County as a whole — one PHZM band and one county frost record, read across 287K 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 San Mateo County Average
San Mateo County Average
- ●USDA Zones 10a, averaged across San Mateo County
- ●One soil character for all of San Mateo County
- ●State-average frost dates
YOUR Parcel
- ✓Your exact zone, not San Mateo County's 10a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in San Mateo County
Pull a site-specific report for your exact address in San Mateo County, California — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that San Mateo County averages can't show:
We read public map data around San Mateo County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the San Mateo County average
How we know this about San Mateo 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 San Mateo County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about San Mateo County
Is it too late to plant in San Mateo County?
No — San Mateo County has no 28°F killing freeze in the 30-year station record, so the growing season is year-round and there is no last-frost date to wait for. Planting is paced by rainfall, heat and daylength instead of by frost: start heat-lovers any month, and time cool-season crops (lettuce, brassicas, peas) for the cooler, wetter half of the year or for higher ground. Succession sowing every few weeks works all year, so the limit is what you can keep watered and harvested, not the calendar.
When does frost risk typically end in San Mateo County?
It doesn't — San Mateo County records no 28°F killing freeze at all across the 1991–2020 station record, so there is no spring frost date to plant after. Cold still matters with elevation: the higher you garden, the cooler the nights, and a few tropical crops sulk below about 60°F even where they never freeze.
How long is the growing season in San Mateo County?
Year-round — the 1991–2020 station record for San Mateo County contains no 28°F killing freeze, so there is no season to measure between freezes. What paces planting instead is heat, rainfall and daylength: the hottest, wettest stretch is the hard part for cool-season crops, not winter. Elevation is the one real exception — the higher you garden, the colder the nights get.
Is the soil safe to grow vegetables in San Mateo County?
The federal record around San Mateo County runs heavier than most — 5,427 documented sites, mostly Brownfields entries (4,961), the nearest Brownfields record about 2.6 miles 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.
Everything above is measured at San Mateo County's scale — its 10a band and its no killing freeze on record. Your yard writes its own version of San Mateo 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 San Mateo County’s own scale
9 of the readings below were taken at San Mateo County's own scale — a 30-year record with no killing freeze in it, the 3 most extensive soil series mapped here and 5,427 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- San Mateo County's own USDA hardiness band, zones 10aUSDA PHZM 2023
- No 28°F killing freeze in San Mateo County's own 30-year station record — a year-round growing season, measured here rather than inheritedNOAA Regional Climate Centers ACIS, 1991-2020
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in San Mateo CountyUSDA NRCS SSURGO
- 5,427 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Brownfields record about 2.6 miles outFederal environmental registers
- San Mateo County's boundary and the 287,105 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 10a and a ~365-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions San Mateo County spans, Coast Range the largestUS EPA Level III Ecoregions
- Open occurrence records documented in San Mateo County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto San Mateo 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 San Mateo County — the ~365 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 San Mateo County's 287,105 acreswhy one lot differs from the next →
- Which of those 5,427 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 San Mateo Countyread your own land →