Siskiyou County, in California, sits in USDA hardiness zone 8a — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
A short list that earns its place here — cabbage, fig, california poppy, and collard greens — with any one site's soil, sun, and drainage making the final cut.
Siskiyou County lies within the Klamath Basin — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Siskiyou County holds more than one microclimate.
Soils and elevations shift across Siskiyou 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 Siskiyou County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Siskiyou County — the short answer
Siskiyou County, California: USDA zone 8a, about 210 days between hard freezes, across 4.0M acres.
- USDA zone
- 8a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 8
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Nov 4
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~210
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 4.0M 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 Siskiyou County's average, not your lot's — a low corner or a tree line moves it. Against Siskiyou County's 210-day season, see what your own ground reads.
Heat in Siskiyou County
Across a year, Siskiyou County accumulates about 2,602 growing degree days above 50°F, about 1,155 fewer than the middle California county — ahead of 13 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 Siskiyou County
Across Siskiyou County, the ground is predominantly Mollisols, where Duzel, Lassen, and Capjac are the most extensive named soil series. The soil is generally well drained with a gravelly loam surface. Topsoil pH runs about 6.3–7.0, neutral. Rainfall drains through hydrologic group C soils.
Soil order
Mollisols
Drainage
Well drained
Hydric soils
12%
Soil still varies lot by lot — soil types explained.
How the ground varies across Siskiyou County
The USDA soil survey maps 68% of Siskiyou County as well drained — but another 30% drains differently: 9% moderately well drained, 6% poorly drained.
Duzel is the most extensive named soil at 3% of mapped acres, then Lassen (3%) and Capjac (3%).
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 Siskiyou County
Each reading below is measured for Siskiyou 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 Siskiyou 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 Siskiyou County runs about pH 6.3–7.0, 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
MeasuredSiskiyou County runs about 210 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
MeasuredSiskiyou 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 Siskiyou County is in
Siskiyou County spans 3 EPA Level III ecoregions — Klamath Mountains/California High North Coast Range (52%), Cascades (27%) and Eastern Cascades Slopes and Foothills (21%). 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 Siskiyou County
We scored all 1,086 plants against Siskiyou County's own USDA zone 8a and its own 210-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 Siskiyou County?
Too late for some crops, right on time for others — a growing season is a sequence, not a deadline. Cool-season crops can go in from around Mar 11; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 8 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 4 — long-season crops need about 90 days of runway, quick greens only 30. Here the season winds down slowly: late sowings, a real autumn harvest, and garlic in the ground before the first hard freeze.
Documented around Siskiyou County
- monarch butterfly11 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Siskiyou County
USGS estimates 8,659 lb of Glyphosate on Siskiyou County farmland in 2019, its largest by weight, ahead of 2,4-d (7,774 lb) and Hexazinone (7,610 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 Siskiyou County — and how to grow with it.
We checked the federal record across Siskiyou County — 903 documented sites across 7 of the 9 source types we track.
The most significant on record: 9 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Siskiyou 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 Siskiyou County
Closest first, across Siskiyou County. Listing isn't leaking, and distance isn't exposure.
- PACIFIC BELLBrownfields · 2.4 mi
- Grenada TexacoUnderground Storage Tanks · 4.0 mi
- BILLY TANNER REPAIRBrownfields · 4.0 mi
- 3 J'S DELI & MINI MART INCBrownfields · 4.0 mi
- TWO JACKS MOBILEBrownfields · 4.1 mi
- 3 J Truck StopUnderground Storage Tanks · 4.1 mi
- GRENADA OIL INC DBA 3 J TRUCK STOPBrownfields · 4.1 mi
- 044N006W22K002MNitrate · 4.1 mi
- COWLEY D&L INCBrownfields · 4.1 mi
- Costa LilyMining · 4.2 mi
- 042N006W03C001MNitrate · 4.7 mi
- SISKIYOU COUNTY ROAD DEPT DISTRICT 3Brownfields · 4.7 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Siskiyou 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 Siskiyou County.
Sources Checked
across Siskiyou County
Severity Distribution
across Siskiyou County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Siskiyou County, Mining runs higher than the national average — 455 sites across Siskiyou County. 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.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Check your specific parcel in Siskiyou 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 Siskiyou County average
Your land is one point inside Siskiyou County
Everything above resolves to Siskiyou County as a whole — one PHZM band and one county frost record, read across 4.0M 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 Siskiyou County Average
Siskiyou County Average
- ●USDA Zones 8a, averaged across Siskiyou County
- ●One soil character for all of Siskiyou County
- ●Frost dates read at Siskiyou County's scale: Apr 8 to Nov 4
YOUR Parcel
- ✓Your exact zone, not Siskiyou County's 8a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Siskiyou County
Pull a site-specific report for your exact address in Siskiyou County, California — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Siskiyou County averages can't show:
We read public map data around Siskiyou County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Siskiyou County average
How we know this about Siskiyou 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 Siskiyou County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Siskiyou County
When does frost risk typically end in Siskiyou County?
The last hard freeze (28°F) in Siskiyou County typically lands around Apr 8, 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 Apr 29.
How long is the growing season in Siskiyou County?
Measured between 28°F hard freezes, Siskiyou County sees about 210 frost-free days — roughly Apr 8 through Nov 4, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 29 to Oct 21, about 175 days.
Is the soil safe to grow vegetables in Siskiyou County?
The federal record around Siskiyou County runs heavier than most — 903 documented sites, mostly Mining entries (455), the nearest Brownfields record about 2.4 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 Siskiyou County's scale — its 8a band and its 210-day season. Your yard writes its own version of Siskiyou 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 Siskiyou County’s own scale
9 of the readings below were taken at Siskiyou County's own scale — its own ~210-day span between 28°F freezes, the 3 most extensive soil series mapped here and 903 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Siskiyou County's own USDA hardiness band, zones 8aUSDA PHZM 2023
- Siskiyou County's own 28°F hard-freeze dates and its ~210-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Siskiyou CountyUSDA NRCS SSURGO
- 903 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Brownfields record about 2.4 miles outFederal environmental registers
- Siskiyou County's boundary and the 4,018,407 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 8a and a ~210-day seasonGrowable Ground crop-matching engine
- The 3 ecoregions Siskiyou County spans, Klamath Mountains/California High North Coast Range the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Siskiyou County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Siskiyou 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 Siskiyou County — the ~210 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 Siskiyou County's 4,018,407 acreswhy one lot differs from the next →
- Which of those 903 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 Siskiyou Countyread your own land →