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

Planting zone for 94820 — El Sobrante, CA

ZIP code 94820 (El Sobrante, Contra Costa County) is in USDA zone 9b: the coldest winter night averages 25 to 30 °F.

Where ZIP 94820 is

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 frostrare
First frostrare
2012 zone10a

Was 10a on the 2012 map — half a zone colder now. 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 El Sobrante, 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

A 32 °F frost doesn't happen here in most winters. At the nearest station (NOAA station Richmond, CA — 6 miles away, elevation 20 ft) the median growing season is 365 days. When frost does come, it is a midwinter night or two; cover tender plants when a freeze is forecast.

Frost data: NOAA NCEI U.S. Climate Normals 1991–2020.

When spring arrived in 2026

In 2026, spring leaf-out near 94820 came on Jan 29 — about the same time as the 1991–2020 average (Jan 28).

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 El Sobrante, CA

The soil mapped at the center of ZIP 94820 is Los Osos — clay loam, well drained.

TextureClay loamholds water and nutrients; slow to drain and warm up
pH6.5neutral; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter3%moderate
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Cut and fill land-Los Osos complex, 9 to 30 percent slopes.

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 94820; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in El Sobrante, CA

Summer high75 °Faverage high, September
Winter low44 °Faverage low, January
Hot days5days a year at 90 °F or more
Freezing nights0nights a year at 32 °F or less
Growing degree days3,322base 50 °F — the season’s usable heat
Longest day14 h 48 mindaylight on June 21
Shortest day9 h 31 mindaylight on December 21
Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully
Precipitation24.2 inper year, rain and melted snow

Average high and low, by month

30°40°50°60°70°80°90°32 °FJanuary: average high 58 °F, low 44 °F 58°44° JanFebruary: average high 61 °F, low 46 °F 61°46° FebMarch: average high 64 °F, low 47 °F 64°47° MarApril: average high 67 °F, low 49 °F 67°49° AprMay: average high 69 °F, low 52 °F 69°52° MayJune: average high 72 °F, low 54 °F 72°54° JunJuly: average high 71 °F, low 55 °F 71°55° JulAugust: average high 72 °F, low 56 °F 72°56° AugSeptember: average high 75 °F, low 56 °F 75°56° SepOctober: average high 73 °F, low 54 °F 73°54° OctNovember: average high 65 °F, low 49 °F 65°49° NovDecember: average high 58 °F, low 44 °F 58°44° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 4.90 in precipitation 4.9 JanFebruary: 4.66 in precipitation 4.7 FebMarch: 3.40 in precipitation 3.4 MarApril: 1.66 in precipitation 1.7 AprMay: 0.83 in precipitation 0.8 MayJune: 0.23 in precipitation 0.2 JunJuly: 0.00 in precipitation 0.0 JulAugust: 0.04 in precipitation 0.0 AugSeptember: 0.11 in precipitation 0.1 SepOctober: 1.11 in precipitation 1.1 OctNovember: 2.50 in precipitation 2.5 NovDecember: 4.80 in precipitation 4.8 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Richmond, CA (6 mi away); precipitation: El Cerrito 1.3 Nw, CA (3 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

945649b
Pinole, CA · 2 mi
9480310a
El Sobrante, CA · 2 mi
9480610a
San Pablo, CA · 2 mi
9480510a
Richmond, CA · 3 mi
945479b
Hercules, CA · 3 mi
9453010a
El Cerrito, CA · 4 mi
9480210a
Richmond, CA · 4 mi
9480710a
Richmond, CA · 4 mi

All 2 ZIP codes in El Sobrante → · California planting zones →

Questions about 94820

What planting zone is ZIP code 94820?

ZIP code 94820 (El Sobrante, 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).

How much rain and snow does 94820 get?

About 24.2 inches of precipitation a year (NOAA 1991–2020 normals, El Cerrito 1.3 Nw station).

How hot do summers get in El Sobrante, CA?

The average high peaks at 75 °F in September, with about 5 days a year at 90 °F or more.

What kind of soil does 94820 have?

The USDA soil survey maps Los Osos at the center of ZIP 94820: clay loam, well drained, pH about 6.5 (neutral).

Did spring come early in El Sobrante, CA in 2026?

Spring leaf-out near 94820 came on Jan 29 in 2026, about the same as the 1991–2020 average (Jan 28), according to the USA National Phenology Network Spring Index.

What kind of onions grow in El Sobrante, CA?

Intermediate onions: the longest day near 94820 is 14 h 48 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 94820 change?

Yes. The 2012 USDA map put 94820 in zone 10a; the 2023 map puts it in zone 9b. The newer map uses 1991–2020 data and more weather stations.