Glenn County, in California, sits in USDA hardiness zone 9a — a zone band wide enough that plant choice, not possibility, is the interesting question.
A short list that earns its place here — artichoke, fig, california poppy, and cabbage — with any one site's soil, sun, and drainage making the final cut.
Glenn County lies within the Sacramento Valley — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Glenn County holds more than one microclimate.
Soils and elevations shift across Glenn 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 Glenn County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Glenn County — the short answer
Glenn County, California: USDA zone 9a, about 309 days between hard freezes, across 841K acres.
- USDA zone
- 9a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Jan 30
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Dec 5
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~309
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 841K 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 9a is Glenn County's average, not your lot's — a low corner or a tree line moves it. Against Glenn County's 309-day season, see what your own ground reads.
Heat and winter chill in Glenn County
Across a year, Glenn County accumulates about 4,716 growing degree days above 50°F, about 959 more than the middle California county — ahead of 47 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 1,281 hours below 45°F, 94 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 Glenn County
Across Glenn County, the ground is predominantly Alfisols, where Sheetiron, Maymen, and Tehama are the most extensive named soil series. The soil is generally well drained with a gravelly loam surface. Topsoil pH runs about 5.8–6.7, slightly acidic. Rainfall drains through hydrologic group D soils.
Soil order
Alfisols
Drainage
Well drained
Hydric soils
9%
Soil still varies lot by lot — soil types explained.
How the ground varies across Glenn County
The USDA soil survey maps 60% of Glenn County as well drained — but another 33% drains differently: 12% somewhat excessively drained, 9% somewhat poorly drained.
Sheetiron is the most extensive named soil at 12% of mapped acres, then Maymen (8%) and Tehama (5%).
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 Glenn County
Each reading below is measured for Glenn 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 Glenn 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 Glenn County runs about pH 5.8–6.7, 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
MeasuredGlenn County runs about 309 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
MeasuredGlenn County sits in USDA hardiness zone 9a.
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 Glenn County is in
Glenn County spans 3 EPA Level III ecoregions — Central California Foothills and Coastal Mountains (46%), Central California Valley (39%) and Klamath Mountains/California High North Coast Range (15%). 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 Glenn County
We scored all 1,086 plants against Glenn County's own USDA zone 9a and its own 309-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 Glenn County?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Jan 2; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Jan 30 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Dec 5 — long-season crops need about 90 days of runway, quick greens only 30. With almost year-round growing weather, timing is about heat and rainfall more than frost — some bench is always in play.
Documented around Glenn County
- monarch butterfly2 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Glenn County
USGS estimates 202,467 lb of Glyphosate on Glenn County farmland in 2019, its largest by weight, ahead of Thiobencarb (101,668 lb) and Azoxystrobin (16,772 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 Glenn County — and how to grow with it.
We checked the federal record across Glenn County — 815 documented sites across 7 of the 9 source types we track.
The most significant on record: 2 Superfund sites (none NPL-listed). 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 Glenn 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 Glenn County
Closest first, across Glenn County. Listing isn't leaking, and distance isn't exposure.
- Avery ClaimsMining · 1.0 mi
- Nye RanchMining · 2.6 mi
- THUNDERHILL RACEWAYBrownfields · 6.1 mi
- 020N004W02Q001MNitrate · 6.7 mi
- Turner RanchMining · 6.8 mi
- JMC BUTTE FARMSBrownfields · 6.8 mi
- 020N004W11H001MNitrate · 7.1 mi
- PACIFIC BELLBrownfields · 7.1 mi
- STONY CREEK JOINT UNIFIED SCHOOL DISTRICTBrownfields · 7.2 mi
- STONY GORGE HYDROELECTRIC FACILITYBrownfields · 7.4 mi
- CALIF OLIVE RANCH INCBrownfields · 7.4 mi
- RATLIFF & DEMMER FARMSBrownfields · 8.1 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Glenn 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 Glenn County.
Total Sites
815
across Glenn County
Risk Level
Elevated
Highest-severity
2 Superfund sites (none NPL-listed)
Sources Checked
across Glenn County
Severity Distribution
across Glenn County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Glenn County, Nitrate runs higher than the national average — 394 sites across Glenn County. It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Check your specific parcel in Glenn 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 Glenn County average
Your land is one point inside Glenn County
Everything above resolves to Glenn County as a whole — one PHZM band and one county frost record, read across 841K 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 Glenn County Average
Glenn County Average
- ●USDA Zones 9a, averaged across Glenn County
- ●One soil character for all of Glenn County
- ●Frost dates read at Glenn County's scale: Jan 30 to Dec 5
YOUR Parcel
- ✓Your exact zone, not Glenn County's 9a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Glenn County
Pull a site-specific report for your exact address in Glenn County, California — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Glenn County averages can't show:
We read public map data around Glenn County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Glenn County average
How we know this about Glenn 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 Glenn County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Glenn County
When does frost risk typically end in Glenn County?
The last hard freeze (28°F) in Glenn County typically lands around Jan 30, 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 20.
How long is the growing season in Glenn County?
Measured between 28°F hard freezes, Glenn County sees about 309 frost-free days — roughly Jan 30 through Dec 5, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Feb 20 to Nov 21, about 274 days.
Is the soil safe to grow vegetables in Glenn County?
The federal record around Glenn County is a meaningful one — 815 documented sites, mostly Nitrate entries (394), the nearest Mining record about 1.0 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 Glenn County's scale — its 9a band and its 309-day season. Your yard writes its own version of Glenn 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 Glenn County’s own scale
9 of the readings below were taken at Glenn County's own scale — its own ~309-day span between 28°F freezes, the 3 most extensive soil series mapped here and 815 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Glenn County's own USDA hardiness band, zones 9aUSDA PHZM 2023
- Glenn County's own 28°F hard-freeze dates and its ~309-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Glenn CountyUSDA NRCS SSURGO
- 815 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Mining record about 1.0 miles outFederal environmental registers
- Glenn County's boundary and the 840,921 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 9a and a ~309-day seasonGrowable Ground crop-matching engine
- The 3 ecoregions Glenn County spans, Central California Foothills and Coastal Mountains the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Glenn County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Glenn 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 Glenn County — the ~309 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 Glenn County's 840,921 acreswhy one lot differs from the next →
- Which of those 815 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 Glenn Countyread your own land →