Generally — Most Areas
radicchio (zones 3-10) suits most of California (4b-11a) — zones 4-10 are in range, and the rest of the state is the exception.
Radicchio in California — the short answer
Radicchio in California: hardy in zones 3–10, full sun, against a state median of ~317 frost-free days.
- Plant zones
- 3-10
- Manual horticultural correction (source not retained); NC State Extension and Missouri Botanical Garden, with the remaining rows from other published sources or Growable Ground compilation
- California zones
- 4b-11a
- USDA PHZM 2023
- Frost window
- Jan 19 - Mar 19 – Nov 29 - Dec 12
- NOAA RCC ACIS 1991-2020, 28°F
- Shortest county season
- 108 days
- NOAA Regional Climate Centers ACIS, 1991-2020, county 28°F killing freeze
- Days to maturity
- 85 days
- Growable Ground Plant Database
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS and university Extension sources — per-field provenance varies and is published with the dataset.
Your yard isn't the whole zone.
California spans zones 4b-11a, but your yard sits in exactly one — and slope, tree cover, and cold-air pockets nudge it further. Enter your address and we'll score radicchio against your parcel's actual hardiness, soil, and sun.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
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California is not one climate
California’s winter-low ladder runs across 58 counties, from zone 6 in Mono County to zone 10.5 in San Francisco County. That is 45°F between the two counties’ average coldest night — the difference between radicchio overwintering in the ground and coming under cover.
The middle half of 58 counties runs 9–9.5 zones, with a median of 9.5 zones — a 4.5-zone span end to end.
Measured across 58 California counties. USDA PHZM 2023, per county. Quartiles are order statistics — every figure shown is a value a real county recorded, not an interpolation. Your own site sits somewhere inside this range; a parcel report resolves where.
Where in California Fits Best
Radicchio is rated for zones 3–10 — a cold floor USDA puts at -40 to -30°F. Against California’s 58 counties that band holds in 56 of them, and the line runs at Mono County (zone 6a), the coldest county still inside it.
Inside zones 3–10
56 counties
- Alpine County · zone 6b
- Lassen County · zone 7a
- Modoc County · zone 7a
3 of 56 shown
Above the zone 10 ceiling
2 counties
- Orange County · zone 10b
- San Francisco County · zone 10b
Too little winter chill rather than too much cold — a low-chill selection is what changes it.
County hardiness zones: USDA Plant Hardiness Zone Map (PHZM) 2023, per county. A zone is a 10°F band of average annual extreme minimum temperature, so the floor above is the band the plant's rating denotes, not a single measured kill point. Slope, shelter and cold-air drainage routinely move a site half a zone either way from its county figure — which is the part only your address resolves.
Even within California's zones 4b-11a, county microclimates differ enough to change what thrives. These counties carry the closest zone match for radicchio (USDA PHZM 2023):
Zone Comparison
Radicchio Needs
- USDA Zones: 3-10
- Frost-Free Days: 90+
- Sun: Full Sun
- Mature size: 1 ft tall
- Picking window: ~14 days of harvest
- Drought tolerance: Medium
California Has
- USDA Zones: 4b-11a
- Last Hard Freeze (28°F): Jan 19 - Mar 19
- First Hard Freeze (28°F): Nov 29 - Dec 12
- Annual Rainfall: 5-80 inches
- Common Soils: Alluvial clay, Sandy loam, Adobe clay
Plant Zone Range (zones 3-10)
Preferred Soil pH
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS, and university Extension sources — per-field provenance varies and is published with the dataset. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant Radicchio in California
The frost window
Across California, the last spring hard freeze (28°F) clears between Jan 19 and Mar 19, and the first fall hard freeze lands between Nov 29 and Dec 12 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 255-day window you can count on — up to 327 days on a mild site in a kind year. That marks the hard freeze, not the last light frost, so tender transplants usually wait another 2-3 weeks.
When to start the seed
Those dates are when radicchio goes out, not when it starts. It is sown under cover about 4 weeks ahead, so counting back from California's late-side last freeze of Mar 19 is what fixes your sowing date — and a yard that clears frost earlier than the state's late date starts earlier still.
Winter standing
California runs as cold as USDA zone 4, and no sourced winter-hardiness floor is on record for radicchio, so this page does not state whether it overwinters here — and gives no fall establishment date on the strength of a guess. Whether radicchio is a permanent planting or a replant-every-spring crop for you turns on your own zone within California; check its hardiness range against that before treating it as long-lived ground.
Frost window: NOAA Climate Normals 1991-2020. Plant timing fields: Growable Ground Plant Database — frost-free days from FAO ECOCROP, days to harvest from university Extension production guides, and growing-degree-day and chill-hour minimums that are compilation estimates rather than published figures. Your site's own frost dates can run earlier or later than the state range — a parcel report pins them down.
Growing Season Fit
The zone check says radicchio survives winter in part of California, not across all of it. Whether the season is long enough — and warm enough — is a different question.
Frost-free days
Radicchio wants 90+ frost-free days; a typical California site sees ~317 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves comfortable headroom for succession planting.
Growing degree days
Radicchio needs ~1300 GDD (base 50°F) to ripen. The state median runs ~4290 GDD (from PRISM 1991-2020 climate normals), so California's typical season clears that easily.
GDD and chill-hour figures are computed from PRISM 1991-2020 monthly climate normals; frost-free days from NOAA Regional Climate Centers ACIS, 1991-2020. Each is the state median across its counties (P25/P75 span the within-state spread). Hardiness-zone range is USDA PHZM 2023.
Soil + Drainage Fit
Radicchio tolerates a wide pH range (pH 4.5-8.3) — 3.8 units, acid ground through alkaline — so soil acidity is rarely what limits it in California. A soil test is still worth having, but for what else it tells you about this site, not to clear this plant. It will grow across that whole span, but it does best between pH 6 and 7.5 — worth knowing before you decide whether a California soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your California site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
Plant pH requirements: FAO ECOCROP and USDA PLANTS, with the remaining rows from other published sources or Growable Ground compilation. Drainage: FAO ECOCROP, with the remaining rows from other published sources or Growable Ground compilation. California soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Before you plant radicchio for food
Anything you grow to eat takes up what is in the ground it grows in, so what is on record near you is worth knowing before radicchio goes in. What follows is California’s documented federal record at state scale — a screening signal, not a soil test, and not a statement about any one lot.
Safe to Grow Here?
What the federal record shows across California — and how to grow with it.
We checked the federal record across California — 254,277 documented sites across 8 of the 9 source types we track.
The most significant on record: 1073 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
California 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.
Severity Distribution
across California
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around California, Brownfields runs higher than the national average — 196,551 sites across California. 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.
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.
What Else to Consider for Radicchio in California
Zone compatibility tells you about winter cold survival — but California growers also need to think about:
Drought is a persistent challenge — irrigation is essential in most regions
Wildfire risk affects rural and foothill properties
Adobe clay soils in valleys drain poorly without amendment
Wide climate variation means plant selection is highly location-specific
What to actually do about these — and the constraints that apply to every California grower, not just radicchio — is covered on the California growing guide.
Timing shifts within California
Radicchio needs about 90 days of frost-free season to complete its cycle. Even Mono County — California’s shortest season at 108 frost-free days — clears that by 18 days, so season length isn’t the constraint anywhere in California. What varies is your own parcel.
Across California’s 57 counties the frost-free season runs from 108 days in Mono County to 365 days in Ventura County — a spread of 257 days, which is why a single statewide planting date misleads. The median California county sees 317 frost-free days, leaving radicchio about 227 days of slack on a typical parcel — room for a second sowing where the season runs long.
County last-freeze dates and frost-free day counts: NOAA Regional Climate Centers ACIS (1991-2020), county 28°F freeze (earlier than the folk 32°F "last frost"). Radicchio's 90-day requirement: USDA PLANTS / Growable Ground plant database (minimum frost-free days). A parcel report resolves your address's own frost dates.
Pollinator + Wildlife Value
Radicchio draws honeybees and native bees (moderate value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, radicchio can only work that bloom inside California's frost window — roughly 317 days, opening after the last 28°F freeze (Jan 19 - Mar 19) and closing at the first (Nov 29 - Dec 12), per NOAA Regional Climate Centers ACIS, 1991-2020.
California Cooperative Extension
For California-specific cultivar recommendations, planting calendars, and pest pressure for radicchio, the canonical source is UC Agriculture and Natural Resources. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Radicchio native to California?
No — the USDA PLANTS Database lists Radicchio as introduced rather than native in the Lower 48, so it is not part of California's native flora. It grows here as a garden plant; pairing it with a few California natives keeps local pollinators fed too.
Looking for plants that belong here? The California growing guide lists USDA-documented natives for the state.
Native-range data: USDA PLANTS Database state-distribution records, accessed 2026-07-01.
Common Questions About Growing Radicchio in California
When can I plant Radicchio in California?
California's last spring hard freeze (28°F) clears between Jan 19 and Mar 19, and the first fall hard freeze lands between Nov 29 and Dec 12 (NOAA Regional Climate Centers ACIS, 1991-2020). No sourced winter-hardiness floor is on record for Radicchio, so this page does not state whether it overwinters in California and publishes no fall establishment date for it — check its hardiness range against your own zone before treating it as a permanent planting.
What hardiness zone is Radicchio grown in across California?
California spans USDA hardiness zones 4b-11a (USDA ARS PHZM 2023). Radicchio carries a range of zones 3-10, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical California site have?
A typical California site sees ~317 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Radicchio needs 90+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date.
Is Radicchio native to California?
No — the USDA PLANTS Database lists Radicchio as introduced rather than native in the Lower 48, so it is not part of California's native flora. It grows here as a garden plant; pairing it with a few California natives keeps local pollinators fed too.
How should I amend the soil for Radicchio in California?
Radicchio tolerates pH 4.5-8.3 and well (dry spells) drainage (FAO ECOCROP). That is a 3.8-unit span, acid ground through alkaline, so pH is rarely what limits this plant on a California site — amend for drainage and organic matter first.
Will Radicchio actually grow on my specific land in California?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores radicchio against your address's exact soil pH, drainage, sun, and frost-date data drawn from USDA SSURGO, NOAA, and PRISM — not state averages.
Check your specific parcel in California
State-level data is a sketch. Your Growable Ground report scores radicchio against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that California radicchio averages can't show:
We read public map data around California — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the California radicchio average
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Growing guides for radicchio
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