Riverside County, in California, sits in USDA hardiness zone 9b — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
Growers here do well with okra, meyer lemon, california poppy, and artichoke — with the usual caveat that any single yard's soil, sun, and drainage cast the deciding vote.
Riverside County lies within the Mojave Desert — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Riverside County holds more than one microclimate.
Soils and elevations shift across Riverside 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 Riverside County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Riverside County — the short answer
Riverside County, California: USDA zone 9b, about 303 days between hard freezes, across 4.6M acres.
- USDA zone
- 9b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Feb 13
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Dec 13
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~303
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 4.6M 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 Riverside County's average, not your lot's — a low corner or a tree line moves it. Against Riverside County's 303-day season, see what your own ground reads.
Heat and winter chill in Riverside County
Across a year, Riverside County accumulates about 5,615 growing degree days above 50°F, about 1,858 more than the middle California county — ahead of 54 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 1,027 hours below 45°F, 160 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 Riverside County
Across Riverside County, the ground is predominantly Entisols, where Cieneba, Pintobasin, and Blackeagle are the most extensive named soil series. The soil is generally somewhat excessively drained with a sandy loam surface. Topsoil pH runs about 6.6–7.9, neutral. Rainfall drains through hydrologic group D soils.
Soil order
Entisols
Drainage
Somewhat excessively drained
Hydric soils
2%
Soil still varies lot by lot — soil types explained.
How the ground varies across Riverside County
The USDA soil survey maps 33% of Riverside County as somewhat excessively drained — but another 53% drains differently: 32% well drained, 13% excessively drained.
Cieneba is the most extensive named soil at 5% of mapped acres, then Pintobasin (3%) and Blackeagle (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 Riverside County
Each reading below is measured for Riverside 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 Riverside County are somewhat excessively 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 Riverside County runs about pH 6.6–7.9, 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
MeasuredRiverside County runs about 303 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
MeasuredRiverside 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 Riverside County is in
Riverside County spans 4 EPA Level III ecoregions — Sonoran Basin and Range (54%), Southern California/Northern Baja Coast (21%), Mojave Basin and Range (16%) and Southern California Mountains (10%). 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 Riverside County
We scored all 1,086 plants against Riverside County's own USDA zone 9b and its own 303-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 Riverside 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 Jan 16; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Feb 13 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Dec 13 — long-season crops need about 90 days of runway, quick greens only 30. Here the calendar nearly circles: cool-season crops take the winter shift, and the next window is always close.
Documented around Riverside County
- monarch butterfly174 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Riverside County
USGS estimates 139,672 lb of Glyphosate on Riverside County farmland in 2019, its largest by weight, ahead of Imidacloprid (10,330 lb) and Dimethoate (6,793 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 Riverside County — and how to grow with it.
We checked the federal record across Riverside County — 12,198 documented sites across 8 of the 9 source types we track.
The most significant on record: 38 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Riverside 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 Riverside County
Closest first, across Riverside County. Listing isn't leaking, and distance isn't exposure.
- JOSEPH'S CLEANERSBrownfields · 1.2 mi
- SO CAL GAS CO CACTUS CITY STATIONBrownfields · 1.2 mi
- COACHELLA WATER AUTHORITYPFAS · 4.4 mi
- ROBERTSON'S READY MIXBrownfields · 6.4 mi
- COACHELLA VALLEY AGGREGATES INCBrownfields · 7.4 mi
- ANGELUS BLOCK COMPANY INCBrownfields · 7.4 mi
- COACHELLA LANDFILLSuperfund · 7.9 mi
- 006S009E19B001SNitrate · 7.9 mi
- SUN WEST TRANSPORT INCBrownfields · 7.9 mi
- WEST COAST AGGREGATE SUPPLY, INC.Brownfields · 7.9 mi
- Winfield No. 2Mining · 7.9 mi
- DOLE DRIED FRUIT & NUT COToxics Release Inventory · 8.6 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Riverside 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 Riverside County.
Severity Distribution
across Riverside County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Riverside County, Brownfields runs higher than the national average — 8,468 sites across Riverside County. It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
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.
Check your specific parcel in Riverside 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 Riverside County average
Your land is one point inside Riverside County
Everything above resolves to Riverside County as a whole — one PHZM band and one county frost record, read across 4.6M 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 Riverside County Average
Riverside County Average
- ●USDA Zones 9b, averaged across Riverside County
- ●One soil character for all of Riverside County
- ●Frost dates read at Riverside County's scale: Feb 13 to Dec 13
YOUR Parcel
- ✓Your exact zone, not Riverside County's 9b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Riverside County
Pull a site-specific report for your exact address in Riverside County, California — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Riverside County averages can't show:
We read public map data around Riverside County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Riverside County average
How we know this about Riverside 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 Riverside County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Riverside County
When does frost risk typically end in Riverside County?
The last hard freeze (28°F) in Riverside County typically lands around Feb 13, 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 Mar 6.
How long is the growing season in Riverside County?
Measured between 28°F hard freezes, Riverside County sees about 303 frost-free days — roughly Feb 13 through Dec 13, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Mar 6 to Nov 29, about 268 days.
Is the soil safe to grow vegetables in Riverside County?
The federal record around Riverside County runs heavier than most — 12,198 documented sites, mostly Brownfields entries (8,468), the nearest Brownfields record about 1.2 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 Riverside County's scale — its 9b band and its 303-day season. Your yard writes its own version of Riverside 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 Riverside County’s own scale
9 of the readings below were taken at Riverside County's own scale — its own ~303-day span between 28°F freezes, the 3 most extensive soil series mapped here and 12,198 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Riverside County's own USDA hardiness band, zones 9bUSDA PHZM 2023
- Riverside County's own 28°F hard-freeze dates and its ~303-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Riverside CountyUSDA NRCS SSURGO
- 12,198 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Brownfields record about 1.2 miles outFederal environmental registers
- Riverside County's boundary and the 4,613,769 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 9b and a ~303-day seasonGrowable Ground crop-matching engine
- The 4 ecoregions Riverside County spans, Sonoran Basin and Range the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Riverside County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Riverside 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 Riverside County — the ~303 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 Riverside County's 4,613,769 acreswhy one lot differs from the next →
- Which of those 12,198 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 Riverside Countyread your own land →