Humboldt 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.
Humboldt County lies within the Pacific Northwest — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Humboldt County holds more than one microclimate.
Soils and elevations shift across Humboldt 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 Humboldt County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Humboldt County — the short answer
Humboldt County, California: USDA zone 9b, about 278 days between hard freezes, across 2.3M acres.
- USDA zone
- 9b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Mar 1
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Dec 4
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~278
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 2.3M 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 Humboldt County's average, not your lot's — a low corner or a tree line moves it. Against Humboldt County's 278-day season, see what your own ground reads.
Heat and winter chill in Humboldt County
Across a year, Humboldt County accumulates about 2,032 growing degree days above 50°F, about 1,725 fewer than the middle California county — ahead of 7 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 1,893 hours below 45°F, 706 more 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 Humboldt County
Across Humboldt County, the ground is predominantly Inceptisols, where Sproulish, Canoecreek, and Tannin are the most extensive named soil series. The soil is generally well drained with a loam surface. Topsoil pH runs about 5.4–6.0, moderately acidic. Rainfall drains through hydrologic group C soils.
Soil order
Inceptisols
Drainage
Well drained
Hydric soils
4%
Soil still varies lot by lot — soil types explained.
How the ground varies across Humboldt County
The USDA soil survey maps 85% of Humboldt County as well drained — but another 13% drains differently: 8% moderately well drained, 2% very poorly drained.
Sproulish is the most extensive named soil at 9% of mapped acres, then Canoecreek (7%) and Tannin (4%).
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 Humboldt County
Each reading below is measured for Humboldt 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 Humboldt 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 Humboldt County runs about pH 5.4–6.0, on the acidic side.
Blueberries, potatoes, and rhododendrons thrive in it, but most vegetables start locking out nutrients below about pH 6.0 and grow pale and stunted no matter how much you feed them.
A measured lime application raises pH for the crops that need it — but test first, because the right rate depends on your own soil, not the county average.
USDA NRCS SSURGO
Season length
MeasuredHumboldt County runs about 278 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
MeasuredHumboldt 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 Humboldt County is in
Humboldt County spans 2 EPA Level III ecoregions — Coast Range (57%) and Klamath Mountains/California High North Coast Range (43%). 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 Humboldt County
We scored all 1,086 plants against Humboldt County's own USDA zone 9b and its own 278-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 Humboldt County?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Feb 1; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Mar 1 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Dec 4 — 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 Humboldt County
- monarch butterfly5 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Humboldt County
USGS estimates 55 lb of Pyraclostrobin on Humboldt County farmland in 2019, its largest by weight, ahead of Glyphosate (32 lb) and Diuron (8 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 Humboldt County — and how to grow with it.
We checked the federal record across Humboldt County — 1,066 documented sites across 8 of the 9 source types we track.
The most significant on record: 12 Superfund sites. 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 Humboldt 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 Humboldt County
Closest first, across Humboldt County. Listing isn't leaking, and distance isn't exposure.
- NEW CINGULAR WIRELESS PCS LLCBrownfields · 2.0 mi
- KNEELAND HELITACK BASEBrownfields · 2.4 mi
- INDRA VALLEY STRATEGIC MARKETING GROUPBrownfields · 2.8 mi
- AT&T MOBILITYBrownfields · 2.9 mi
- Several Unlocatable MinesMining · 3.3 mi
- UnknownMining · 3.3 mi
- NEW LEAF INTERIOR PLANT SERVICEBrownfields · 5.2 mi
- CNTY HUMBOLDT FRESHWATER MAINTENANCE STNBrownfields · 8.6 mi
- CUMMINGS ROAD SANITARY LANDFILLSuperfund · 9.4 mi
- EUREKA, CITY OFPFAS · 9.8 mi
- ARCATA, CITY OFPFAS · 10.2 mi
- 006N002E31R001HNitrate · 10.7 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Humboldt 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 Humboldt County.
Severity Distribution
across Humboldt County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Humboldt County, two things run higher than the national average across Humboldt County — Mining (94 sites) and Brownfields (784 sites). That's not a problem with your land — it's information about it.
Mining: Mining sites — both historic and active — can leach heavy metals (arsenic, lead, cadmium, mercury) into soil and water for centuries after operations cease.
Brownfields: Brownfield sites are former commercial or industrial properties where legacy soil contamination (heavy metals, PAHs, petroleum compounds) may persist.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Check EPA brownfield remediation status — many sites have completed cleanup with institutional controls.
Check your specific parcel in Humboldt 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 Humboldt County average
Your land is one point inside Humboldt County
Everything above resolves to Humboldt County as a whole — one PHZM band and one county frost record, read across 2.3M 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 Humboldt County Average
Humboldt County Average
- ●USDA Zones 9b, averaged across Humboldt County
- ●One soil character for all of Humboldt County
- ●Frost dates read at Humboldt County's scale: Mar 1 to Dec 4
YOUR Parcel
- ✓Your exact zone, not Humboldt County's 9b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Humboldt County
Pull a site-specific report for your exact address in Humboldt County, California — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Humboldt County averages can't show:
We read public map data around Humboldt County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Humboldt County average
How we know this about Humboldt 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 Humboldt County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Humboldt County
When does frost risk typically end in Humboldt County?
The last hard freeze (28°F) in Humboldt County typically lands around Mar 1, 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 Mar 22.
How long is the growing season in Humboldt County?
Measured between 28°F hard freezes, Humboldt County sees about 278 frost-free days — roughly Mar 1 through Dec 4, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Mar 22 to Nov 20, about 243 days.
Is the soil safe to grow vegetables in Humboldt County?
The federal record around Humboldt County is a meaningful one — 1,066 documented sites, mostly Brownfields entries (784), the nearest Brownfields 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 Humboldt County's scale — its 9b band and its 278-day season. Your yard writes its own version of Humboldt 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 Humboldt County’s own scale
9 of the readings below were taken at Humboldt County's own scale — its own ~278-day span between 28°F freezes, the 3 most extensive soil series mapped here and 1,066 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Humboldt County's own USDA hardiness band, zones 9bUSDA PHZM 2023
- Humboldt County's own 28°F hard-freeze dates and its ~278-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Humboldt CountyUSDA NRCS SSURGO
- 1,066 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Brownfields record about 2.0 miles outFederal environmental registers
- Humboldt County's boundary and the 2,283,534 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 9b and a ~278-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions Humboldt County spans, Coast Range the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Humboldt County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Humboldt 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 Humboldt County — the ~278 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 Humboldt County's 2,283,534 acreswhy one lot differs from the next →
- Which of those 1,066 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 Humboldt Countyread your own land →