Planting zone for 91801 — Alhambra, CA
ZIP code 91801 (Alhambra, Los Angeles County) is in USDA zone 10a: the coldest winter night averages 30 to 35 °F.
Where ZIP 91801 is
Outlined: the ZIP code area · tap the map for the zone at any spot · scroll or pinch to zoomNot 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.
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 10a means →
Frost forecast — next 7 nights
live from the National Weather ServiceLoading the forecast for Alhambra, 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 San Gabriel Fire Dept, CA — 2 miles away, elevation 364 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 91801 came on Jan 17 — 3 days earlier than the 1991–2020 average (Jan 20).
Jan 202026
Jan 17
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 Alhambra, CA
The soil mapped at the center of ZIP 91801 is Azuvina — loam, well drained. Much of the area is built over (urban land); this is the natural soil underneath.
Map unit: Urban land-Azuvina-Montebello complex, 0 to 5 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 91801; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.
Climate in Alhambra, CA
Average high and low, by month
Precipitation by month inches
NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: San Gabriel Fire Dept, CA (2 mi away); precipitation: San Gabriel Fire Dept, CA (2 mi away). Daylight is calculated from latitude.
Nearby ZIP codes
2 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.
Questions about 91801
What planting zone is ZIP code 91801?
ZIP code 91801 (Alhambra, CA) is in USDA hardiness zone 10a on the 2023 map: the coldest night of an average winter reaches 30 to 35 °F (−1.1 to 1.7 °C).
How much rain and snow does 91801 get?
About 15.7 inches of precipitation a year (NOAA 1991–2020 normals, San Gabriel Fire Dept station).
How hot do summers get in Alhambra, CA?
The average high peaks at 88 °F in August, with about 65 days a year at 90 °F or more.
What kind of soil does 91801 have?
The USDA soil survey maps Azuvina at the center of ZIP 91801: loam, well drained, pH about 7.9 (alkaline).
Did spring come early in Alhambra, CA in 2026?
Spring leaf-out near 91801 came on Jan 17 in 2026, 3 days earlier than the 1991–2020 average (Jan 20), according to the USA National Phenology Network Spring Index.
What kind of onions grow in Alhambra, CA?
Intermediate onions: the longest day near 91801 is 14 h 26 min, so day-neutral types bulb best; long-day varieties may not bulb fully.