Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated

Planting zone for 94574 — Saint Helena, CA

ZIP code 94574 (Saint Helena, Napa County) is in USDA zone 9b: the coldest winter night averages 25 to 30 °F. The median last spring frost is April 7 and the first fall frost December 5.

Where ZIP 94574 is

Outlined: the ZIP code area · tap the map for the zone at any spot · scroll or pinch to zoom

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.

Zone9b25 to 30 °F
Coldest night−3.9 to −1.1 °C
Last frostApr 7
First frostDec 5
2012 zone9b

Same zone as on the 2012 map. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 9b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Saint Helena, CA…

Forecast data: National Weather Service (api.weather.gov), public domain. This is not a warning service — for official frost and freeze warnings see weather.gov.

Frost dates in Saint Helena, CA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 7median — 50% chance of a later frost
Safe for tender plantsApril 30only 10% chance of frost after
First fall frostDecember 5median — 10% chance by Nov 14
Growing season245 daysfrost-free, median

A hard freeze (28 °F) usually ends around February 18 and returns around December 30.

From the NOAA station Angwin Pacific Union College, CA — 2 miles away, elevation 1,716 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 94574

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Feb 24 – Mar 10
SpinachSow outdoors · Feb 24 – Mar 17
Broccoli, cabbageStart indoors · Jan 27 – Feb 10
Broccoli, cabbageTransplant · Mar 17 – Mar 31
Onion setsPlant outdoors · Mar 10 – Mar 24
PotatoesPlant outdoors · Mar 17 – Mar 31
LettuceSow outdoors · Mar 10 – Mar 24
Carrots, beetsSow outdoors · Mar 17 – Mar 31
TomatoesStart indoors · Feb 10 – Feb 24
TomatoesTransplant · Apr 14 – Apr 28
Peppers, eggplantStart indoors · Jan 27 – Feb 10
Peppers, eggplantTransplant · Apr 21 – May 5
BeansSow outdoors · Apr 14 – Apr 28
Sweet cornSow outdoors · Apr 14 – Apr 28
Cucumbers, squashSow outdoors · Apr 14 – Apr 28
Fall lettuce, spinachSow outdoors · Oct 10 – Oct 24
GarlicPlant cloves · Nov 21 – Dec 26
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 7) and first fall frost (Dec 5) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 94574 came on Jan 23 — 9 days earlier than the 1991–2020 average (Feb 1).

JanFebMarAprMayJun

The Spring Index marks the day when accumulated warmth is enough for lilac and honeysuckle to leaf out — a widely used signal that the growing season has started. Source: USA National Phenology Network, www.usanpn.org — Spring Indices, first leaf, 2026 (data as of 2026-09-08) and 30-year average 1991–2020 (CC BY 4.0).

Soil in Saint Helena, CA

The soil mapped at the center of ZIP 94574 is Forward — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer
pH5.5moderately acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter70%high
Hydrologic groupCwater soaks in slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Forward silt loam, 12 to 57 percent slopes, MLRA 15.

Soil Survey Staff, Natural Resources Conservation Service, USDA. Soil Survey Geographic (SSURGO) Database, via Soil Data Access, accessed 2026-10-29. The soil at the center point of ZIP 94574; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Saint Helena, CA

Summer high85 °Faverage high, July
Winter low39 °Faverage low, January
Hot days27days a year at 90 °F or more
Freezing nights15nights a year at 32 °F or less
Growing degree days3,278base 50 °F — the season’s usable heat
Longest day14 h 52 mindaylight on June 21
Shortest day9 h 28 mindaylight on December 21
Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully
Precipitation39.7 inper year, rain and melted snow

Average high and low, by month

30°40°50°60°70°80°90°100°32 °FJanuary: average high 54 °F, low 39 °F 54°39° JanFebruary: average high 56 °F, low 40 °F 56°40° FebMarch: average high 60 °F, low 41 °F 60°41° MarApril: average high 66 °F, low 42 °F 66°42° AprMay: average high 73 °F, low 47 °F 73°47° MayJune: average high 80 °F, low 51 °F 80°51° JunJuly: average high 85 °F, low 54 °F 85°54° JulAugust: average high 84 °F, low 54 °F 84°54° AugSeptember: average high 81 °F, low 53 °F 81°53° SepOctober: average high 72 °F, low 50 °F 72°50° OctNovember: average high 60 °F, low 43 °F 60°43° NovDecember: average high 53 °F, low 39 °F 53°39° Dec

Precipitation by month inches

0″2″4″6″8″January: 7.80 in precipitation 7.8 JanFebruary: 7.59 in precipitation 7.6 FebMarch: 5.50 in precipitation 5.5 MarApril: 2.37 in precipitation 2.4 AprMay: 1.56 in precipitation 1.6 MayJune: 0.36 in precipitation 0.4 JunJuly: 0.01 in precipitation 0.0 JulAugust: 0.04 in precipitation 0.0 AugSeptember: 0.17 in precipitation 0.2 SepOctober: 1.92 in precipitation 1.9 OctNovember: 4.09 in precipitation 4.1 NovDecember: 8.30 in precipitation 8.3 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Angwin Pacific Union College, CA (2 mi away); precipitation: Angwin Pacific Union College, CA (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

1 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

945769b
Deer Park, CA · 3 mi
945089b
Angwin, CA · 3 mi
945739b
Rutherford, CA · 6 mi
945629b
Oakville, CA · 8 mi
945679a
Pope Valley, CA · 9 mi
954529b
Kenwood, CA · 10 mi
945999b
Yountville, CA · 10 mi
954099b
Santa Rosa, CA · 10 mi

California planting zones →

Questions about 94574

What planting zone is ZIP code 94574?

ZIP code 94574 (Saint Helena, CA) is in USDA hardiness zone 9b on the 2023 map: the coldest night of an average winter reaches 25 to 30 °F (−3.9 to −1.1 °C).

When is the last frost in Saint Helena, CA?

The median last spring frost (32 °F) near 94574 is April 7; after April 30 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Angwin Pacific Union College station.

When is the first frost in Saint Helena, CA?

The median first fall frost near 94574 is December 5, giving a median frost-free growing season of 245 days.

When should I plant tomatoes in 94574?

Start tomato seeds indoors around Feb 10 – Feb 24 and set transplants outside around Apr 14 – Apr 28, one to three weeks after the median last frost.

How much rain and snow does 94574 get?

About 39.7 inches of precipitation a year (NOAA 1991–2020 normals, Angwin Pacific Union College station).

How hot do summers get in Saint Helena, CA?

The average high peaks at 85 °F in July, with about 27 days a year at 90 °F or more.

What kind of soil does 94574 have?

The USDA soil survey maps Forward at the center of ZIP 94574: slightly decomposed plant material, well drained, pH about 5.5 (moderately acidic).

Did spring come early in Saint Helena, CA in 2026?

Spring leaf-out near 94574 came on Jan 23 in 2026, 9 days earlier than the 1991–2020 average (Feb 1), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Saint Helena, CA?

Intermediate onions: the longest day near 94574 is 14 h 52 min, so day-neutral types bulb best; long-day varieties may not bulb fully.