Imperial 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.
The conditions favor okra, meyer lemon, california poppy, and artichoke, among others — though every individual site edits that list with its own soil, sun, and drainage.
Imperial County lies within the Imperial Valley and the Sonoran Desert — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Imperial County holds more than one microclimate.
Soils and elevations shift across Imperial 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 Imperial County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Imperial County — the short answer
Imperial County, California: USDA zone 9b, about 344 days between hard freezes, across 2.7M acres.
- USDA zone
- 9b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Jan 15
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Dec 25
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~344
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 2.7M 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 9b is Imperial County's average, not your lot's — a low corner or a tree line moves it. Against Imperial County's 344-day season, see what your own ground reads.
Heat and winter chill in Imperial County
Across a year, Imperial County accumulates about 8,280 growing degree days above 50°F, about 4,523 more than the middle California county — ahead of every other California county. 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 428 hours below 45°F, 759 fewer 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 Imperial County
Across Imperial County, the ground is predominantly Entisols, where Imperial, Indio, and Rositas are the most extensive named soil series. The soil is generally moderately well drained with a silty clay surface. Topsoil pH runs about 8.2, moderately alkaline. Rainfall drains through hydrologic group C soils.
Soil order
Entisols
Drainage
Moderately well drained
Hydric soils
0%
Soil still varies lot by lot — soil types explained.
How the ground varies across Imperial County
The USDA soil survey maps 73% of Imperial County as moderately well drained — but another 22% drains differently: 15% well drained, 7% somewhat excessively drained.
Imperial is the most extensive named soil at 73% of mapped acres, then Indio (5%) and Rositas (4%).
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 Imperial County
Each reading below is measured for Imperial 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 Imperial County are moderately well drained, in hydrologic group C — roughly the middle of the drainage range.
This is close to the middle most vegetables prefer: it holds enough water to carry a crop between rains without staying waterlogged. The catch is that a wet spring or a low corner can still tip it soggy.
Plant on the site as-is for most crops, but keep the lowest, slowest-draining beds for moisture-tolerant plantings.
USDA NRCS SSURGO
Surface pH
MeasuredTopsoil across Imperial County runs about pH 8.2, on the alkaline side.
Many vegetables cope, but acid-lovers like blueberries struggle, and iron and manganese lock up above about pH 7.5 — leaves yellow between the veins even in rich soil.
Elemental sulfur and generous organic matter lower pH slowly for the beds that need it; test first so you add only what the soil actually calls for.
USDA NRCS SSURGO
Season length
MeasuredImperial County runs about 344 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
MeasuredImperial County sits in USDA hardiness zone 9b.
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 Imperial County is in
Imperial County sits in the Sonoran Basin and Range — EPA Level III, inside the wider North American Deserts. One consistent ecological setting across the whole county.
What Grows in Imperial County
We scored all 1,086 plants against Imperial County's own USDA zone 9b and its own 344-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 Imperial County?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Jan 1; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Jan 15 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Dec 25 — long-season crops need about 90 days of runway, quick greens only 30. And with a calendar this mild, the honest answer is that planting barely stops — winter opens seasons colder regions never see.
Documented around Imperial County
- monarch butterfly4 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Imperial County
USGS estimates 180,359 lb of Imidacloprid on Imperial County farmland in 2019, its largest by weight, ahead of Glyphosate (114,003 lb) and 2,4-d (50,245 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 Imperial County — and how to grow with it.
We checked the federal record across Imperial County — 1,452 documented sites across 7 of the 9 source types we track.
The most significant on record: 10 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Imperial 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 Imperial County
Closest first, across Imperial County. Listing isn't leaking, and distance isn't exposure.
- GALEN OLESH FARMS LLCBrownfields · 0.9 mi
- 013S015E01Q001SNitrate · 1.0 mi
- 013S015E01B001SNitrate · 1.7 mi
- TIMOTHY R ALLEN DBA TASCO, INCBrownfields · 2.0 mi
- 013S016E16F001SNitrate · 2.1 mi
- STEVE REEVES RANCHESBrownfields · 3.0 mi
- ARROWHEAD APPLICATORS INCBrownfields · 3.2 mi
- 013S015E03N001SNitrate · 3.6 mi
- BRAWLEY, CITY OFPFAS · 3.6 mi
- 012S015E27R001SNitrate · 3.9 mi
- J EMANUELLI & SONSBrownfields · 4.1 mi
- CHAPARRAL APPLICATORS INCBrownfields · 4.3 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Imperial 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 Imperial County.
Sources Checked
across Imperial County
Severity Distribution
across Imperial County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Imperial County, two things run higher than the national average across Imperial County — Brownfields (992 sites) and PFAS (12 sites). That's not a problem with your land — it's information about it.
Brownfields: Brownfield sites are former commercial or industrial properties where legacy soil contamination (heavy metals, PAHs, petroleum compounds) may persist.
PFAS: PFAS (per- and polyfluoroalkyl substances) are called "forever chemicals" because they do not biodegrade.
Check EPA brownfield remediation status — many sites have completed cleanup with institutional controls.
Test irrigation water source — this is the primary pathway for PFAS to reach garden crops.
Check your specific parcel in Imperial 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 Imperial County average
Your land is one point inside Imperial County
Everything above resolves to Imperial County as a whole — one PHZM band and one county frost record, read across 2.7M 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 Imperial County Average
Imperial County Average
- ●USDA Zones 9b, averaged across Imperial County
- ●One soil character for all of Imperial County
- ●Frost dates read at Imperial County's scale: Jan 15 to Dec 25
YOUR Parcel
- ✓Your exact zone, not Imperial County's 9b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Imperial County
Pull a site-specific report for your exact address in Imperial County, California — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Imperial County averages can't show:
We read public map data around Imperial County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Imperial County average
How we know this about Imperial 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 Imperial County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Imperial County
When does frost risk typically end in Imperial County?
The last hard freeze (28°F) in Imperial County typically lands around Jan 15, 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 5.
How long is the growing season in Imperial County?
Measured between 28°F hard freezes, Imperial County sees about 344 frost-free days — roughly Jan 15 through Dec 25, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Feb 5 to Dec 11, about 309 days.
Is the soil safe to grow vegetables in Imperial County?
The federal record around Imperial County runs heavier than most — 1,452 documented sites, mostly Brownfields entries (992), the nearest Brownfields record about 0.9 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 Imperial County's scale — its 9b band and its 344-day season. Your yard writes its own version of Imperial 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 Imperial County’s own scale
9 of the readings below were taken at Imperial County's own scale — its own ~344-day span between 28°F freezes, the 3 most extensive soil series mapped here and 1,452 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Imperial County's own USDA hardiness band, zones 9bUSDA PHZM 2023
- Imperial County's own 28°F hard-freeze dates and its ~344-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Imperial CountyUSDA NRCS SSURGO
- 1,452 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Brownfields record about 0.9 miles outFederal environmental registers
- Imperial County's boundary and the 2,672,288 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 9b and a ~344-day seasonGrowable Ground crop-matching engine
- Imperial County sitting wholly inside the Sonoran Basin and RangeUS EPA Level III Ecoregions
- Open occurrence records documented in Imperial County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Imperial 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 Imperial County — the ~344 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 Imperial County's 2,672,288 acreswhy one lot differs from the next →
- Which of those 1,452 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 Imperial Countyread your own land →