St. Helena, California, sits in USDA hardiness zone 9b — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
Well-matched crops include okra, meyer lemon, california poppy, and artichoke, and the gap between "grows in the area" and "grows in your yard" is closed by soil, sun, and drainage.
Even in St. Helena, no two yards are alike.
A low spot, a south-facing slope, or a stand of trees moves the frost date and sun across a single St. Helena lot. 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 St. Helena — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
St. Helena — the short answer
St. Helena, California: USDA zone 9b, about 327 days between hard freezes, across 3K acres of city.
- USDA zone
- 9b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Jan 23
- Napa County normal — NOAA 1991–2020, nearest to this town
- First hard freeze (28°F)
- Dec 16
- Napa County normal — NOAA 1991–2020, nearest to this town
- Days between freezes
- ~327
- Napa County normal — NOAA 1991–2020, nearest to this town
- City area
- 3K acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. No 30-year normal resolves at this town’s own centroid, so the hard-freeze dates are Napa County’s — the closest measured record, labelled as such rather than passed off as local.
Hardiness Zone Range
Zone 9b is St. Helena's average, not your lot's — a low corner or a tree line moves it. Against St. Helena's 327-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in St. Helena
Each reading below is measured for St. Helena itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
From county recordsSt. Helena runs about 327 days between hard freezes (read from Napa County, the closest normal to St. Helena) — 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
MeasuredSt. Helena 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 St. Helena is in
St. Helena sits in the Central California Foothills and Coastal Mountains — EPA Level III, inside the wider Mediterranean California. That is read at St. Helena's own centroid rather than borrowed from Napa County.
What Grows in St. Helena
Every plant below cleared St. Helena's own zone 9b and its 327-day season. Each card opens that plant's California profile. How we score.
Is it too late to plant in St. Helena?
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 23 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Dec 16 — long-season crops need about 90 days of runway, quick greens only 30. In a climate this gentle, “too late” hardly applies — the question becomes which crops prefer the cooler months ahead.
What's on the federal record near St. Helena
Closest first, within ~10 miles of St. Helena. Listing isn't leaking, and distance isn't exposure.
- ETS LABORATORIES INCBrownfields · 1700 ft
- JIM WHEELER PAINTINGBrownfields · 2000 ft
- GREGORY S MINNICK DBA FULTON AUTO BODYBrownfields · 2000 ft
- NAPA COUNTY - ENVIRONMENTAL MGMTBrownfields · 2100 ft
- BERINGER VINEYARDSBrownfields · 2400 ft
- SAFEWAY STORE #2605Brownfields · 0.5 mi
- USPSBrownfields · 0.5 mi
- STEVES HARDWARE INCBrownfields · 0.5 mi
- NAPA VALLEY PETROLEUM INC DBA ST HELENA CHEVRONBrownfields · 0.5 mi
- ST HELENA CHEVRONUnderground Storage Tanks · 0.5 mi
- NAPA RTE 29 DRAINAGE IMPROVEMENTBrownfields · 0.5 mi
- KISSICK WIND MACHINES, LLCBrownfields · 0.5 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from St. Helena'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 St. Helena.
Total Sites
367
within ~10 miles of St. Helena
Risk Level
High
Highest-severity
3 Superfund sites (none NPL-listed)
Sources Checked
within ~10 miles of St. Helena
Severity Distribution
within ~10 miles of St. Helena
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around St. Helena, two things run higher than the national average within ~10 miles of St. Helena — Mining (55 sites) and Brownfields (232 sites). That's not a problem with your land — it's information about it.
Mining: Mining sites — both historic and active — can leach heavy metals (arsenic, lead, cadmium, mercury) into soil and water for centuries after operations cease.
Brownfields: Brownfield sites are former commercial or industrial properties where legacy soil contamination (heavy metals, PAHs, petroleum compounds) may persist.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Check EPA brownfield remediation status — many sites have completed cleanup with institutional controls.
Check your specific parcel in St. Helena
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 St. Helena average
Your land is one point inside St. Helena
Everything above resolves to St. Helena as a whole — one PHZM band, read across 3K acres, with hard-freeze dates borrowed from Napa County’s record because no 30-year normal resolves at this city’s own centroid. 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 city 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 local average.
Your Lot vs the St. Helena Average
St. Helena Average
- ●USDA Zones 9b, averaged across St. Helena
- ●One soil character for all of St. Helena
- ●Frost dates read at St. Helena's scale: Jan 23 to Dec 16
YOUR Parcel
- ✓Your exact zone, not St. Helena's 9b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in St. Helena
Pull a site-specific report for your exact address in St. Helena, California — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that St. Helena averages can't show:
We read public map data around St. Helena — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the St. Helena average
How we know this about St. Helena
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this city’s own centroid; hard-freeze dates from NOAA 1991–2020 28°F normals at Napa County’s record, because none resolves here; boundaries and acreage from US Census TIGER/Line 2025; the contamination records from the federal sources named in their beats above. Soil is not read at city grain anywhere on this page — there is no city-resolution survey in our data, which is why you will find no soil grid here rather than a statewide one wearing a local label. The resolution ledger below names every figure this page inherited.
Common questions about St. Helena
When does frost risk typically end in St. Helena?
The last hard freeze (28°F) in St. Helena typically lands around Jan 23, 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 13.
When is the first frost in St. Helena?
The first hard freeze (28°F) in St. Helena typically arrives around Dec 16, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Dec 2, so the watching starts about Nov 16 — about 327 days after the spring freeze cleared.
How long is the growing season in St. Helena?
Measured between 28°F hard freezes, St. Helena sees about 327 frost-free days — roughly Jan 23 through Dec 16, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Feb 13 to Dec 2, about 292 days.
Is the soil safe to grow vegetables in St. Helena?
The federal record around St. Helena runs heavier than most — 367 documented sites, mostly Brownfields entries (232), the nearest Brownfields record about 0.3 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.
How do I protect my plants from frost in St. Helena?
From about Nov 16 the job here turns from planting to protecting — the last start even a 30-day crop can finish. As the season closes around the first 28°F hard freeze near Dec 16 (NOAA 1991–2020 climate normals), three moves buy time: row cover or an old sheet over tender plants on still, clear nights; water the soil the afternoon before a freeze, so it holds warmth overnight; and harvest tomatoes, peppers and basil before Dec 16. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at St. Helena's scale — its 9b band and its 327-day season. Your yard writes its own version of St. Helena's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
What this page reads at St. Helena’s own scale
5 of the readings below were taken at St. Helena's own scale — the 3,175 acres it covers and 367 documented sites around it; 5 are borrowed from a wider read, named and linked below.
Measured here
- St. Helena's own USDA hardiness band, zones 9bUSDA PHZM 2023
- 367 documented contamination sites on the federal record near St. Helena, the closest Brownfields record about 0.3 miles out from the town centreFederal environmental registers
- St. Helena's boundary and the 3,175 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 9b and a ~327-day seasonGrowable Ground crop-matching engine
- The ecoregion at St. Helena's own centroid, the Central California Foothills and Coastal MountainsUS EPA Level III Ecoregions
Inherited from a wider read
- The 28°F hard-freeze dates — St. Helena has no normal of its own, so its county's is the closest measured readfrom Napa County
- Soil character — no town-scale survey exists, so St. Helena's 3,175 acres read through its county's SSURGO summaryfrom Napa County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Napa County
- The growing challenges every California grower plans around — written at state scale, so they stay on the state guidefrom California
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Napa County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among St. Helena's 3,175 acreswhy one lot differs from the next →
- Which side of St. Helena you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 3,175 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Brownfields record about 0.3 miles out, measured from the town centrehow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — measured at your address, and averaged away by any St. Helena-wide figureread your own land →
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