Garden Climate for Alpine, CA 91901

Zone 9b · Last frost ~Feb 12 · Soil 65.2°F today (modeled) · See your place on the 2023 USDA zone map

Public NOAA/USDA data, updated 2026-10-16 19:24 UTC.

USDA Plant Hardiness Zone Map · Alpine focus

2023 USDA Plant Hardiness Zone Map around ZIP 91901, marker at Alpine, CA
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USDA Plant Hardiness Zone Map, 2023. Agricultural Research Service, U.S. Department of Agriculture. Accessed from https://planthardiness.ars.usda.gov/. Rendered unaltered from the PRISM Group, Oregon State University GIS data (https://prism.oregonstate.edu, accessed 15 Oct 2026) with official zone colors. Roads (TIGER/Line 2023 primary roads), place names (2023 Gazetteer) and state lines (2023 cartographic boundaries 1:500k) are drawn on top. Source: U.S. Census Bureau.

Zone
9b
USDA 2023 · 25 to 30°F
Last frost
Feb 12
avg last frost (50%)
Soil temp Modeled
65.2°F
↓ 11.6° in 7 days
Chill hours
—
starts Nov 1
Rain
3.08″
since Oct 1 · normal 0.26″

Frost dates for 91901

Last spring frost
Feb 12
50% odds
First fall frost
Dec 24
50% odds
Safer spring date
Mar 20
10% chance of later frost
Growing season
317
days (50%)

Earliest-risk fall date (10%): Dec 2.

NOAA NCEI U.S. Climate Normals 1991-2020, annual/seasonal freeze probabilities (32F) · CA ALPINE (USC00040136) 2.3 km away 21 yrs of record · 364 ft lower than this ZIP

Newsletter · 91901

Frost alerts and planting reminders for 91901. Coming soon.

Ad strip · leaderboard 970×90 / 728×90

7-day forecast · High / Low / Rain / Frost / Wind

High wind: 2 day(s) with gusts ≥40 mph. Stake and protect transplants.
Fri 16
82° 67° gust 62 mph 💧11%
High wind
Sat 17
79° 60° gust 51 mph 💧11%
High wind
Sun 18
80° 60° gust 22 mph 💧0%
Clear
Mon 19
78° 57° gust 16 mph 💧7%
Clear
Tue 20
68° 53° gust 32 mph 💧64% · 0.02″
Rain
Wed 21
63° 50° gust 25 mph 💧69% · 0.56″
Rain
Thu 22
63° 50° gust 20 mph 💧30% · 0.08″
Clear

NOAA NWS api.weather.gov (SGX). Frost = low ≤32°F · High wind = gust ≥40 mph · 💧 = chance of precipitation and expected amount (NWS quantitative precipitation forecast; blank when NWS gives none) · Rain = chance ≥50%.

What to grow when · 91901

Calendar: San Diego County, inland valleys (guide Regions 3-4). Planting months from UC Master Gardeners of San Diego County; Master Gardener Association of San Diego County. Harvest months add typical days-to-harvest. This month also checks live soil temperature and the 7-day frost forecast. The harvest planner uses the same calendar. Rules: methodology.

Affiliate links (disclosed). Placeholders, no partners yet:Frost clothSoil thermometer

Questions about 91901

What USDA hardiness zone is 91901?

ZIP 91901 (Alpine, CA) is in USDA zone 9b (25 to 30°F average annual extreme minimum), per the 2023 USDA Plant Hardiness Zone Map.

When is the last frost in 91901?

Based on NOAA 1991–2020 normals at Ca Alpine (2.3 km away), the median last 32°F freeze is Feb 12. In 1 of 10 years it is after Mar 20. The median first fall freeze is Dec 24.

Nearby ZIP codes

91931 Guatay 91916 Descanso 92021 El Cajon 91935 Jamul 92019 El Cajon 92040 Lakeside

Sources for this page

  • Location: US Census Bureau 2023 Gazetteer, ZCTA internal point
  • Zone: USDA Plant Hardiness Zone Map 2023, ZIP datasets (USDA ARS + PRISM Climate Group, Oregon State University)
  • Frost: NOAA NCEI U.S. Climate Normals 1991-2020, annual/seasonal freeze probabilities (32F) CA ALPINE (USC00040136) 2.3 km away 21 yrs of record · 364 ft lower than this ZIP
  • Forecast: NOAA National Weather Service api.weather.gov (7-day forecast + gridpoint wind gusts)
  • Soil: Open-Meteo forecast API soil model (non-commercial terms)
  • Chill: Iowa Environmental Mesonet ASOS archive (NWS/FAA METAR routine + special obs; one value per clock hour)
  • Raw data: /data/zip/91901.json