Colusa County, in California, sits in USDA hardiness zone 9b — enough range to grow cool-season vegetables, hardy fruit, and warm-season crops that mature before the first hard frost.
These conditions suit avocado, meyer lemon, tomato, and grape — a starting list any specific site will trim or extend with its own soil, sun, and drainage.
Colusa County lies within the Sacramento Valley and the California Central Valley — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring
Colusa County holds more than one microclimate.
Soils and elevations shift across Colusa County, so your frost dates and drainage aren't the county average. Enter your address and we'll score 1,112 plants against your land's actual soil, sun, and frost.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
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Quick Facts
USDA Zones
9b
Last Frost (state avg.)
Jan 15 - May 15
First Frost (state avg.)
Oct 1 - Dec 31
County Area
736K acres
Hardiness Zone Range
Growing Season
Zone maps are averages across Colusa County. Your yard's slope, trees, and frost pockets shift what actually grows — see your land's exact reading.
Soil in Colusa County
Across Colusa County, the ground is predominantly Vertisols, where Willows, Millsholm, and Westfan are the most extensive named soil series. The soil is generally well drained with a loam surface. Topsoil pH runs about 6.3–7.4, neutral. Rainfall drains through hydrologic group D soils.
Soil order
Vertisols
Drainage
Well drained
Hydric soils
26%
Soil still varies lot by lot — soil types explained.
What Grows in Colusa County
Plants matched to Colusa County's USDA zones 9b — each links to its full growing profile.
Growing Challenges in California
What an experienced grower plans around here — each one has a move.
Drought is a persistent challenge — irrigation is essential in most regions
Design the water system before the plants: drip lines plus a thick mulch layer run a full garden on surprisingly little water.
Wildfire risk affects rural and foothill properties
Keep plantings low, lean, and well-watered near structures — your extension office publishes firewise landscaping guides for your county.
Adobe clay soils in valleys drain poorly without amendment
Work in compost over seasons, or skip the fight with a raised bed — adobe's nutrients are excellent once drainage is solved.
Wide climate variation means plant selection is highly location-specific
Zones run 5a to 11a in one state — check your exact zone before trusting any statewide planting list.
For cultivar selection, pest pressure, and planting-time guidance specific to California, the UC Agriculture and Natural Resources is the authoritative local source.
Safe to Grow Here?
What the federal record shows across Colusa County — and how to grow with it.
We checked the federal record across Colusa County — 635 documented sites across 7 of the 9 source types we track.
The most significant on record: 1 Superfund site. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Colusa 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.
Environmental Intelligence
Understanding what's nearby helps you make informed decisions about where and how to grow.
Sources Checked
across Colusa County
Severity Distribution
across Colusa County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Colusa County, two things run higher than the national average — Nitrate (320 sites) and Mining (51 sites). Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
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 well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Check your specific parcel in Colusa County
Get exact proximity distances to contamination sources for your specific parcel — plus soil, sun, drainage, and 1,112 plant recommendations.
Three things about your exact spot that zone averages miss:
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources analyzed in seconds
Your Specific Parcel Matters
Colusa County Average
- ●USDA Zones 9b
- ●Generic soil type for the area
- ●State-average frost dates
YOUR Parcel
- ✓Your exact hardiness zone
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Colusa County
Pull a site-specific report for your exact address in Colusa County, California — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your exact spot that zone averages miss:
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources analyzed in seconds
Key Growing Facts for Colusa County, California
- USDA Hardiness Zones: 9b (USDA PHZM 2023)
- Last Spring Frost (state avg.): Jan 15 - May 15 (NOAA 30-Year Climate Normals)
- First Fall Frost (state avg.): Oct 1 - Dec 31 (NOAA 30-Year Climate Normals)
- County Land Area: 736K acres (US Census TIGER 2025)
Zone data: USDA ARS Plant Hardiness Zone Map 2023. Climate data: NOAA NCEI. County boundaries: US Census TIGER/Line 2025.
Frost dates here are the Colusa County average. Low spots and tree cover move them by days on any one yard — see your exact frost windows.
Frequently Asked Questions
What hardiness zone is Colusa County, California?
Colusa County sits in USDA hardiness zone 9b, per the USDA Plant Hardiness Zone Map 2023. Zones reflect average annual extreme minimum temperatures from 1991–2020 weather data.
When does frost risk typically end in Colusa County?
Colusa County follows California's statewide frost window: last spring frost around Jan 15 - May 15 and first fall frost around Oct 1 - Dec 31, per NOAA 30-year climate normals (1991–2020). Frost dates shift with elevation and local microclimate, so watch your own site's cold pockets.
What vegetables grow in Colusa County?
Colusa County's zone 9b supports a wide range — strong performers include Avocado, Meyer Lemon, Tomato, Grape, and Fig. What actually takes on any one site comes down to its soil, sun, and drainage, and we score each plant against the real conditions at your address.
Which hardiness zone is Colusa County, really?
Officially, Colusa County sits in USDA zone 9b (USDA PHZM 2023) — but a zone is a 30-year average of winter's coldest night across an area, and it can't see any one yard. A south-facing slope, a tree line, or a low frost pocket can shift a single site by half a zone either way, which is why neighboring gardeners often quote different numbers. We read the conditions at your exact address — soil, sun, slope, and frost — and score 1,112 plants against what's actually there.
Is the soil safe to grow vegetables in Colusa County?
The federal record around Colusa County runs heavier than most — 635 documented sites — 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.
Just moved to Colusa County — what should I know before planting?
Start with three facts. Colusa County sits in USDA zone 9b, which sets what survives winter; the statewide frost window runs about Jan 15 - May 15 to Oct 1 - Dec 31 (NOAA 30-year climate normals); and 635 documented sites sit on the federal record here, so a soil test before food beds is the smart first step. From there, matching plants to your actual soil and sun is the fun part.
Everything on this page is a Colusa County average. Your yard writes its own version — 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.