Sonoma County, in California, sits in USDA hardiness zone 9b — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
On paper, okra, meyer lemon, california poppy, and artichoke all suit these conditions — on the ground, soil, sun, and drainage make the final call.
Sonoma County lies within Sonoma — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Sonoma County holds more than one microclimate.
Soils and elevations shift across Sonoma 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 Sonoma County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Sonoma County — the short answer
Sonoma County, California: USDA zone 9b, about 323 days between hard freezes, across 1.0M acres.
- USDA zone
- 9b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Jan 23
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Dec 12
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~323
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 1.0M 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 Sonoma County's average, not your lot's — a low corner or a tree line moves it. Against Sonoma County's 323-day season, see what your own ground reads.
Heat and winter chill in Sonoma County
Across a year, Sonoma County accumulates about 3,287 growing degree days above 50°F, about 470 fewer than the middle California county — ahead of 17 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 1,118 hours below 45°F, 69 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 Sonoma County
Across Sonoma County, the ground is predominantly Inceptisols, where Hugo, Laughlin, and Josephine are the most extensive named soil series. The soil is generally well drained with a loam surface. Topsoil pH runs about 5.8–6.5, slightly acidic. Rainfall drains through hydrologic group C soils.
Soil order
Inceptisols
Drainage
Well drained
Hydric soils
8%
Soil still varies lot by lot — soil types explained.
How the ground varies across Sonoma County
The USDA soil survey maps 66% of Sonoma County as well drained — but another 32% drains differently: 21% moderately well drained, 5% somewhat poorly drained.
Hugo is the most extensive named soil at 17% of mapped acres, then Laughlin (7%) and Josephine (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 Sonoma County
Each reading below is measured for Sonoma 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 Sonoma County are well drained, in hydrologic group C — 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 Sonoma County runs about pH 5.8–6.5, 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
MeasuredSonoma County runs about 323 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
MeasuredSonoma 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 Sonoma County is in
Sonoma County spans 2 EPA Level III ecoregions — Central California Foothills and Coastal Mountains (74%) and Coast Range (26%). 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 Sonoma County
We scored all 1,086 plants against Sonoma County's own USDA zone 9b and its own 323-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 Sonoma County?
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 23 (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. Here the calendar nearly circles: cool-season crops take the winter shift, and the next window is always close.
Documented around Sonoma County
- monarch butterfly149 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Sonoma County
USGS estimates 56,361 lb of Glyphosate on Sonoma County farmland in 2019, its largest by weight, ahead of Cyprodinil (10,888 lb) and Pyrimethanil (3,708 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 Sonoma County — and how to grow with it.
We checked the federal record across Sonoma County — 3,415 documented sites across 7 of the 9 source types we track.
The most significant on record: 16 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Sonoma 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 Sonoma County
Closest first, across Sonoma County. Listing isn't leaking, and distance isn't exposure.
- Unnamed ProspectMining · 2500 ft
- Wall SpringsMining · 1.4 mi
- Archer TractMining · 1.8 mi
- Wall TractMining · 1.9 mi
- ArcherMining · 1.9 mi
- GF WINES, LLC DBA GARY FARRELL WINERYBrownfields · 2.0 mi
- Unnamed LocationMining · 2.0 mi
- 008N009W31C005MNitrate · 2.1 mi
- 008N009W31C003MNitrate · 2.1 mi
- 008N009W20N001MNitrate · 2.2 mi
- SONOMA COUNTY WATER AGENCYBrownfields · 2.2 mi
- VON RENNER CONSTRUCTION & EXCAVATION INCBrownfields · 2.2 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Sonoma 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 Sonoma County.
Sources Checked
across Sonoma County
Severity Distribution
across Sonoma County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Sonoma County, Brownfields runs higher than the national average — 2,768 sites across Sonoma County. 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 Sonoma 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 Sonoma County average
Your land is one point inside Sonoma County
Everything above resolves to Sonoma County as a whole — one PHZM band and one county frost record, read across 1.0M 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 Sonoma County Average
Sonoma County Average
- ●USDA Zones 9b, averaged across Sonoma County
- ●One soil character for all of Sonoma County
- ●Frost dates read at Sonoma County's scale: Jan 23 to Dec 12
YOUR Parcel
- ✓Your exact zone, not Sonoma County's 9b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Sonoma County
Pull a site-specific report for your exact address in Sonoma County, California — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Sonoma County averages can't show:
We read public map data around Sonoma County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Sonoma County average
How we know this about Sonoma 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 Sonoma County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Sonoma County
When does frost risk typically end in Sonoma County?
The last hard freeze (28°F) in Sonoma County typically lands around Jan 23, 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 13.
How long is the growing season in Sonoma County?
Measured between 28°F hard freezes, Sonoma County sees about 323 frost-free days — roughly Jan 23 through Dec 12, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Feb 13 to Nov 28, about 288 days.
Is the soil safe to grow vegetables in Sonoma County?
The federal record around Sonoma County runs heavier than most — 3,415 documented sites, mostly Brownfields entries (2,768), the nearest Mining record about 0.5 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 Sonoma County's scale — its 9b band and its 323-day season. Your yard writes its own version of Sonoma 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 Sonoma County’s own scale
9 of the readings below were taken at Sonoma County's own scale — its own ~323-day span between 28°F freezes, the 3 most extensive soil series mapped here and 3,415 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Sonoma County's own USDA hardiness band, zones 9bUSDA PHZM 2023
- Sonoma County's own 28°F hard-freeze dates and its ~323-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Sonoma CountyUSDA NRCS SSURGO
- 3,415 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Mining record about 0.5 miles outFederal environmental registers
- Sonoma County's boundary and the 1,008,215 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 9b and a ~323-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions Sonoma County spans, Central California Foothills and Coastal Mountains the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Sonoma County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Sonoma 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 Sonoma County — the ~323 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 Sonoma County's 1,008,215 acreswhy one lot differs from the next →
- Which of those 3,415 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 Sonoma Countyread your own land →