Trinity County, in California, sits in USDA hardiness zone 8a — room for a real mix of vegetables, fruit, and perennials matched to the local frost calendar.
Growers here do well with cabbage, fig, california poppy, and collard greens — with the usual caveat that any single yard's soil, sun, and drainage cast the deciding vote.
Trinity County lies within the Shasta Cascade — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Trinity County holds more than one microclimate.
Soils and elevations shift across Trinity 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 Trinity County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Trinity County — the short answer
Trinity County, California: USDA zone 8a, about 204 days between hard freezes, across 2.0M acres.
- USDA zone
- 8a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 27
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Nov 17
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~204
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 2.0M 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 8a is Trinity County's average, not your lot's — a low corner or a tree line moves it. Against Trinity County's 204-day season, see what your own ground reads.
One county, several growing seasons
Trinity County's hard-freeze record runs about 204 days between freezes — but that is the county-wide average, and several towns inside it carry a markedly different season in their own 30-year record: Burnt Ranch at about 247 days and Douglas City at 247 (against the county's ~204).
Those are measured records, not estimates. If you garden in one of these pockets, plant against your own town's season rather than the county's ~204-day average.
NOAA Regional Climate Centers ACIS (1991–2020), 30-year daily minimum record. Only held-out towns carrying their own record are named — a town with no record of its own is absent rather than estimated, and a county with nothing qualifying shows no spread at all.
Heat in Trinity County
Across a year, Trinity County accumulates about 2,211 growing degree days above 50°F, about 1,546 fewer than the middle California county — ahead of 8 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.
Grounded in PRISM Climate Group, Oregon State University — 1991–2020 monthly normals
Soil in Trinity County
Across Trinity County, the ground is predominantly Alfisols, where Hopland, Yorkville, and Hoosimbim are the most extensive named soil series. The soil is generally well drained with a loam surface. Topsoil pH runs about 6.1–6.7, slightly acidic. Rainfall drains through hydrologic group C soils.
Soil order
Alfisols
Drainage
Well drained
Hydric soils
1%
Soil still varies lot by lot — soil types explained.
How the ground varies across Trinity County
The USDA soil survey maps 79% of Trinity County as well drained — but another 20% drains differently: 12% somewhat excessively drained, 5% moderately well drained.
Hopland is the most extensive named soil at 11% of mapped acres, then Yorkville (5%) and Hoosimbim (2%).
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 Trinity County
Each reading below is measured for Trinity 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 Trinity 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 Trinity County runs about pH 6.1–6.7, 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
MeasuredTrinity County runs about 204 days between hard freezes — a long growing season.
There is slack for succession plantings and slow-finishing crops: many vegetables can be sown twice, and the heat-lovers have time to ripen fully.
Plan a second sowing of quick crops after the first comes out, and use the fall window most gardeners let sit idle.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredTrinity County sits in USDA hardiness zone 8a.
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 Trinity County is in
Trinity County sits in the Klamath Mountains/California High North Coast Range — EPA Level III, inside the wider Northwestern Forested Mountains. One consistent ecological setting across the whole county.
What Grows in Trinity County
We scored all 1,086 plants against Trinity County's own USDA zone 8a and its own 204-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 Trinity 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 Mar 30; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 27 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 17 — long-season crops need about 90 days of runway, quick greens only 30. There is slack in a calendar like this — late plantings, second rounds of favorites, and a fall bench that keeps beds working.
Documented around Trinity County
- monarch butterfly5 documented records
Sighting records, so they follow observers as much as insects.
Safe to Grow Here?
What the federal record shows across Trinity County — and how to grow with it.
We checked the federal record across Trinity County — 431 documented sites across 7 of the 9 source types we track.
The most significant on record: 4 Superfund sites (none NPL-listed). Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Trinity 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 Trinity County
Closest first, across Trinity County. Listing isn't leaking, and distance isn't exposure.
- UnnamedMining · 1.1 mi
- JUNCTION CITY TRANSFER STATIONBrownfields · 6.3 mi
- Three B SMining · 6.7 mi
- Phillpot OccurrenceMining · 6.8 mi
- PhillpotMining · 6.8 mi
- TRINITY PUBLIC UTILITIES DISTRICTBrownfields · 7.0 mi
- SHASTA TRINITY NATIONAL FOREST DISPOSAL OF ILLEGAL MARIJUANA GROW SITE CHEMICALSBrownfields · 7.0 mi
- USDA USFS R05 HAYFORK CABrownfields · 7.0 mi
- 2019 ILLEGAL MARIJUANA GROW SITES WASTE REMOVALBrownfields · 7.0 mi
- HAYFORK HIGH SCHOOLBrownfields · 7.2 mi
- CHEEK SKYLINE LOGGINGSuperfund · 7.2 mi
- STILLWELL AUTO WRECKING AND RECYCLINGBrownfields · 7.5 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Trinity 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 Trinity County.
Total Sites
431
across Trinity County
Risk Level
High
Highest-severity
4 Superfund sites (none NPL-listed)
Sources Checked
across Trinity County
Severity Distribution
across Trinity County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Trinity County, Mining runs higher than the national average — 305 sites across Trinity County. Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
Mining: Mining sites — both historic and active — can leach heavy metals (arsenic, lead, cadmium, mercury) into soil and water for centuries after operations cease.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Check your specific parcel in Trinity 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 Trinity County average
Your land is one point inside Trinity County
Everything above resolves to Trinity County as a whole — one PHZM band and one county frost record, read across 2.0M 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 Trinity County Average
Trinity County Average
- ●USDA Zones 8a, averaged across Trinity County
- ●One soil character for all of Trinity County
- ●Frost dates read at Trinity County's scale: Apr 27 to Nov 17
YOUR Parcel
- ✓Your exact zone, not Trinity County's 8a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Trinity County
Pull a site-specific report for your exact address in Trinity County, California — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Trinity County averages can't show:
We read public map data around Trinity County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Trinity County average
How we know this about Trinity 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 Trinity County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Trinity County
When does frost risk typically end in Trinity County?
The last hard freeze (28°F) in Trinity County typically lands around Apr 27, 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 May 18.
How long is the growing season in Trinity County?
Measured between 28°F hard freezes, Trinity County sees about 204 frost-free days — roughly Apr 27 through Nov 17, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 18 to Nov 3, about 169 days.
Is the soil safe to grow vegetables in Trinity County?
The federal record around Trinity County runs heavier than most — 431 documented sites, mostly Mining entries (305), the nearest Mining record about 1.1 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 Trinity County's scale — its 8a band and its 204-day season. Your yard writes its own version of Trinity 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 Trinity County’s own scale
8 of the readings below were taken at Trinity County's own scale — its own ~204-day span between 28°F freezes, the 3 most extensive soil series mapped here and 431 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Trinity County's own USDA hardiness band, zones 8aUSDA PHZM 2023
- Trinity County's own 28°F hard-freeze dates and its ~204-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Trinity CountyUSDA NRCS SSURGO
- 431 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Mining record about 1.1 miles outFederal environmental registers
- Trinity County's boundary and the 2,034,729 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 8a and a ~204-day seasonGrowable Ground crop-matching engine
- Trinity County sitting wholly inside the Klamath Mountains/California High North Coast RangeUS EPA Level III Ecoregions
- Open occurrence records documented in Trinity County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
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 Trinity County — the ~204 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 Trinity County's 2,034,729 acreswhy one lot differs from the next →
- Which of those 431 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 Trinity Countyread your own land →