The California Delta spans USDA hardiness zone 9b — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
Where the Sacramento and San Joaquin rivers braid into a maze of levee-ringed islands, the afternoon "Delta breeze" draws cool marine air off San Francisco Bay through the Carquinez Strait — tempering the interior valley's heat and stretching the frost-free season past 330 days in the western Delta (Solano and Contra Costa counties, per county_data.json). Behind the levees lie the black organic peat and muck soils of the reclaimed islands, the ground that made this California's historic Bartlett-pear and asparagus country and now grows cool-loving Clarksburg-AVA wine grapes like Chenin Blanc. It is the one corner of the Central Valley where a maritime influence, not just the sun, sets the growing rules. These conditions suit tomato, artichoke, fig, and california poppy — a starting list any specific site will trim or extend with its own soil, sun, and drainage.
The California Delta spans California.
Your yard isn't all of the California Delta.
The California Delta spans USDA zones 9b, but your parcel sits in exactly one — and slope, tree cover, and low spots nudge it further. 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 California Delta — soil, climate, flood, and parcel records. How we handle your address.
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The California Delta — the short answer
The California Delta: USDA zones 9b, 321–335 frost-free days, in California.
- USDA zones
- 9b
- USDA PHZM 2023, aggregated over the footprint
- Frost-free season
- 321–335 days
- NOAA Regional Climate Centers ACIS, 1991-2020
- Counties
- 5
- US Census TIGER/Line 2025
- Region type
- County cluster
- Growable Ground growing-region registry
Region boundary: Growable Ground growing-region registry — curated county clusters, EPA Level III ecoregions, and town clusters drawn finer than any county. Where a region publishes no measured season, no season figure is shown.
Hardiness Zone Range
What Grows in the California Delta
Plants matched to the California Delta's USDA zones 9b, ordered by how much hardiness margin each has across the region — the ones with room to spare at both ends of this band lead. Each links to its full growing profile.
Native Plants of the California Delta
Plants the USDA PLANTS Database documents as native and present in this region’s state, kept only where the published hardiness range meets the California Delta’s USDA zones 9b — closest range match first. Presence is recorded by state, so a plant can be documented across the state and still be scarce in your corner of the region.
The ground across the California Delta
The USDA soil survey maps this ground county by county. These are those records weighted by land area across five member counties — this region’s own profile, not a state figure.
The ground is predominantly Alfisols, at 28% of mapped acres, followed by Mollisols (25%), Vertisols (19%) and Inceptisols (12%). Seven soil orders appear somewhere inside the footprint, which is the honest reason a regional soil answer only goes so far. The most extensive named soils are San Joaquin, Capay, and Altamont.
39% of those acres are well drained, and another 22% moderately well drained, 12% poorly drained. Topsoil pH runs 5.8–7.5 between the lowest and the highest county on record.
Soil order
Alfisols
Drainage
Well drained
Topsoil pH
5.8–7.5
Hydric soils
27%
Soil changes across a driveway, so which of these your own ground sits on is a parcel question rather than a regional one. San Joaquin County holds the most wetland ground here, at 35% — soil types explained.
USDA NRCS SSURGO via Soil Data Access
What this means for growing in the California Delta
The soil survey reads this ground county by county, and the readings above are those records summed across the California Delta. Here is what they mean for a garden here — and the move an experienced grower makes about each one.
Drainage
From county records39% of the mapped acres across the California Delta are well drained — ground that drains quickly. That is area-weighted across all five of its mapped counties.
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
From county recordsTopsoil across the California Delta runs pH 5.8–7.5 — near neutral in all five of them.
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
Wet ground
From county recordsAbout 27% of the ground across the California Delta is mapped as hydric — wetland — soil. San Joaquin County carries the most, at 35%.
If your lot falls in one of those pockets, a standard in-ground bed will fight waterlogging all season, and roots that need air will struggle.
Check how your own ground drains before you dig; raised beds or moisture-loving plantings turn a wet corner from a problem into a niche.
USDA NRCS SSURGO
Safe to Grow Here?
What the federal record shows across the California Delta — and how to grow with it.
Across the California Delta's 5 counties the federal record holds 22,193 documented sites, mostly Brownfields (18,421), Nitrate (1,750) and Underground Storage Tanks (1,392). The heaviest single county is Sacramento County, with 6,887.
That is a regional count, not a reading of any one lot — proximity to a documented site is information, not a diagnosis. Open the map outlined to the California Delta to see which records sit where you actually grow.
Sources Checked
Summed across the 5 counties in the California Delta
A note from Gnorman
What an experienced grower watches for around here
In and around the California Delta, Brownfields runs higher than the national average — 18,421 sites across the 5 counties in the California Delta. Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
Brownfields: Brownfield sites are former commercial or industrial properties where legacy soil contamination (heavy metals, PAHs, petroleum compounds) may persist.
Check EPA brownfield remediation status — many sites have completed cleanup with institutional controls.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
Your land is one point inside the California Delta
Everything above resolves to the California Delta as a whole — a footprint spanning USDA zones 9b. Your parcel sits in exactly one of them. 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 region 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 regional average.
Your Lot vs the California Delta Average
California Delta Average
- ●USDA Zones 9b, averaged across California Delta
- ●One soil character for all of California Delta
- ●State-average frost dates
YOUR Parcel
- ✓Your exact zone, not California Delta's 9b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in the California Delta
Pull a site-specific report for your exact address in the California Delta — soil, sun, drainage, frost risk, contamination, and scored plant recommendations.
Three things about your lot that California Delta averages can't show:
We read public map data around The California Delta — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the California Delta average
How we know this about the California Delta
The boundary: a cluster of neighboring counties. Growing regions have no official boundary, so this footprint is our published one, and every figure on this page was measured over the counties inside it rather than borrowed from the state around it.
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, aggregated across the footprint; the growing season from NOAA Regional Climate Centers ACIS 1991–2020 28°F normals, read at each member’s own record; boundaries from US Census TIGER/Line 2025; the contamination record from the federal sources named in that beat above; the soil from the USDA NRCS SSURGO survey, read at each member county’s own record and weighted to this footprint by land area. Where a member carries no record of its own, it is absent from the figure rather than filled in.
Common questions about the California Delta
What hardiness zone is the California Delta?
The California Delta spans USDA hardiness zones 9b, aggregated from the USDA Agricultural Research Service Plant Hardiness Zone Map 2023 across the region's counties. Zones reflect average annual extreme minimum temperatures from 1991–2020 data.
How long is the growing season in the California Delta?
Measured between 28°F hard freezes, the California Delta's counties mostly run 324 to 334 frost-free days, median 332 (NOAA Regional Climate Centers ACIS, 1991–2020, over 5 member counties). That 10-day spread is the honest read — no single season describes 5 counties, and each county guide below carries its own.
When does frost risk end in the California Delta?
Across the California Delta, the middle half of member counties see their last 28°F hard freeze between Jan 16 and Jan 22 (median Jan 17), and their first fall freeze between Dec 12 and Dec 16. Those are hard freezes, not the last light frost: tender transplants wait for about Feb 7, and elevation decides which end of a 6-day spread you garden in.
What grows well in the California Delta?
The California Delta's conditions suit plants such as Tomato, Artichoke, Fig, California Poppy, Rosemary, Olive. What actually thrives on any one site still turns on its specific soil, sun, and drainage — we score each plant against the real conditions at your address.
How is the California Delta defined?
The California Delta is defined here as a curated cluster of 5 neighboring counties that share a growing character. Growing regions have no official boundary, so this footprint is our published one — every county in it is named on this page.
Which states does the California Delta cover?
The California Delta spans California. Each state's full growing guide is linked on this page.
What other growing regions cover the same states?
Pacific Northwest, California Central Valley, Sacramento Valley, San Joaquin Valley, Sierra Nevada Foothills, and Sonoran Desert share at least one state with the California Delta. Growing regions overlap and interlock — a single address can sit inside more than one, which is why the precise read is always the parcel, not the region.
What this page reads at the California Delta’s own scale
6 of the readings below were taken at the California Delta's own scale — the zone 9b band across its footprint, a median 332-day season across its 5 counties and 22,193 documented federal contamination records across its 5 counties, 6,887 of them in Sacramento County alone; one is borrowed from a wider read, named and linked below.
Measured here
- The USDA hardiness band 9b aggregated across all 5 counties in the footprintUSDA PHZM 2023
- The boundary itself — the 5 counties this region is curated fromGrowable Ground subregion registry
- The growing character that makes this region distinct from the states it crossesGrowable Ground subregion registry
- The 28°F season across the footprint — the middle half of its 5 counties run 324 to 334 frost-free days, median 332NOAA Regional Climate Centers ACIS, 1991-2020
- The federal contamination record over the whole footprint — 22,193 documented federal contamination records across its 5 counties, 6,887 of them in Sacramento County aloneEPA, USGS and USDA federal site records
- The soil order mix across the footprint — 28% Alfisols, topsoil pH 5.8–7.5, area-weighted across its 5 mapped countiesUSDA NRCS SSURGO
Inherited from a wider read
- The candidate plant list — its state's curated sets, merged and filtered to zones 9bfrom California
What this page can’t tell you
- Which end of the 10-day range your ground sits at — 324 days at one extreme, 334 at the other, decided mostly by elevationfrost dates explained →
- Which of those soils your own ground sits on — the survey maps them county-wide, and they change across a drivewaysoil types explained →
- The soil pH, drainage, sun hours, and frost pockets on one specific lotwhy one lot differs from the next →
Explore the California Delta
State growing guides
Counties in this region
Other growing regions across California
The maritime Northwest west of the Cascade crest — mild, wet winters and dry summers behind berries, tree fruit, and lush cool-season gardens. (Union of the west-side ecoregions.)
A vast flat alluvial trough with hot dry summers and rich soils — one of the most productive agricultural regions on earth, from almonds and stone fruit to row crops.
The cooler, wetter northern half of the Central Valley — rice, walnuts, tomatoes, and orchard fruit on rich alluvial bottomland.
The hot southern half of California's Central Valley — deep soils and intense sun behind almonds, stone fruit, grapes, and row crops at vast scale.
California's Gold Country foothills — rocky, well-drained slopes and warm days that suit wine grapes, olives, and Mediterranean orchard crops.
A warm desert of saguaro and palo verde with mild winters that allow desert citrus, dates, and prickly pear alongside intensive irrigated gardening.