Garden Climate for El Cajon, La Mesa, Lakeside area: 91942, 91978, 92019, 92020, 92021, 92040, 92071, 92119

Zone 10b · Last frost ~Jan 6 · Soil 70.8°F today (modeled) · See your place on the 2023 USDA zone map

ZIPs in this area

What differs between these ZIPs: elevation, zone, soil temperature. Everything else on this page is the same for all of them. The page below shows 91942 (closest to the area's middle elevation).

ZIP	Town	Elevation	Zone	Last frost	First frost	Chill hrs last season	Soil now
91942	La Mesa	582 ft	10b	Jan 6	Dec 21	266	70.8°F
91978	Spring Valley	513 ft	10b	Jan 6	Dec 21	266	65.5°F
92019	El Cajon	671 ft	10b	Jan 6	Dec 21	266	71.1°F
92020	El Cajon	435 ft	10a	Jan 6	Dec 21	266	70.4°F
92021	El Cajon	735 ft	10a	Jan 6	Dec 21	266	69.0°F
92040	Lakeside	411 ft	10a	Jan 6	Dec 21	266	66.3°F
92071	Santee	338 ft	10a	Jan 6	Dec 21	266	70.5°F
92119	San Diego	659 ft	10b	Jan 6	Dec 21	266	67.8°F

Why grouped: these are urban and suburban lowland ZIPs (under about 1,500 ft and within 40 km of the ocean) whose numbers are close: median last frost dates within about two weeks of each other, last season's chill hours all in the 100-300 range, the same inland setting and the same 820 ft elevation band. Each ZIP still uses its own nearest suitable stations; see the table for exact values.

Public NOAA/USDA data, updated 2026-10-16 18:57 UTC.

USDA Plant Hardiness Zone Map · La Mesa focus

Zone

10b

USDA 2023 · 35 to 40°F

Last frost

Jan 6

avg last frost (50%)

Soil temp Modeled

70.8°F

↓ 6.8° in 7 days

Chill hours

—

starts Nov 1

Rain

1.31″

since Oct 1 · normal 0.19″

Frost dates for 91942

Last spring frost

Jan 6

50% odds

First fall frost

Dec 21

50% odds

Safer spring date

Feb 7

10% chance of later frost

Growing season

350

days (50%)

Earliest-risk fall date (10%): Dec 1.

NOAA NCEI U.S. Climate Normals 1991-2020, annual/seasonal freeze probabilities (32F) · CA EL CAJON (USC00042706) 8.7 km away 27 yrs of record · 85 ft lower than this ZIP

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

Fri 16

92° 71° gust 35 mph 💧6%

Clear

Sat 17

89° 64° gust 22 mph 💧6%

Clear

Sun 18

88° 64° gust 16 mph 💧0%

Clear

Mon 19

83° 62° gust 15 mph 💧8%

Clear

Tue 20

73° 59° gust 25 mph 💧68% · 0.05″

Rain

Wed 21

70° 57° gust 23 mph 💧68% · 0.45″

Rain

Thu 22

68° 57° gust 17 mph 💧31% · 0.11″

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 · 91942

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 cloth Soil thermometer

Harvest planner

Create an interactive chart of your garden plan to see estimated harvest times, harvest size, and get recommendations based on your unique growing plan!

Open planner for 91942 →

Soil temperature Modeled

Daily average 70.8°F on 2026-10-15, mean of 6 cm and 18 cm model layers (~4-5 in). Modeled

7-day trend: 77.6 → 76.0 → 71.3 → 68.4 → 67.2 → 67.4 → 70.8

Source: Open-Meteo forecast API soil model (non-commercial terms).

Why modeled: no operational USCRN within 60 km and 300 m elevation

Chill hours this season

This season

—

Counting starts Nov 1

Last year by today

—

Counting starts Nov 1

10-year average by today

—

Counting starts Nov 1

Last season's total

266

Nov 1–Apr 30 · 2025-26 · 98% of hours recorded

All values are hours between 32°F and 45°F. Observed at SAN DIEGO/GILLESPIE (SEE) 6.4 km away · 197 ft lower than this ZIP · Iowa Environmental Mesonet ASOS archive (NWS/FAA METAR routine + special obs; one value per clock hour). Chill hours = observed hours with 32F <= T <= 45F, counted from Nov 1. Missing hours are not filled. Past seasons use the same station and method; the average only includes seasons with >=80% hourly coverage.

Rainfall this season

This water year (since Oct 1)

1.31″

Oct 1–Oct 15 · 87% of days recorded · Oct 1–Oct 5 El Cajon (GHCN) + Oct 6–Oct 15 Gillespie (airport ASOS)

Last year by Oct 15

0.37″

Oct 1–Oct 15, 2025 · 100% of days recorded

30-yr normal by Oct 15

0.19″

Oct 1–Oct 15 · NOAA 1991–2020 normal · full water year 11.63″

Last water year total

10.88″

Oct 1 2025–Sep 30 2026 · 100% of days recorded

Rain and melted snow, inches. Observed at CA EL CAJON (USC00042706) 8.7 km away · 85 ft lower than this ZIP · NOAA NCEI GHCN-Daily (values with a quality flag are skipped; daily reports usually lag a few days to weeks, latest Oct 5). Normal: NOAA NCEI U.S. Climate Normals 1991–2020 (daily). Season starts Oct 1 (water year (Oct 1–Sep 30)). Days after Oct 5 come from SAN DIEGO/GILLESPIE (SEE) 6.4 km away · 197 ft lower than this ZIP: Iowa Environmental Mesonet ASOS daily summary (METAR precipitation; a reporting day with no precip group counts as 0.00). That station uses the same distance, elevation and coastal rules; only this water year is filled. Comparisons run through the last complete day.

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Zone border tip

The 2023 USDA map puts 91942's point in zone 10b. The nearest different zone (10a) is about 3.8 km away on the map. That's close, so if you garden on that side, base plant choices on your exact spot, not the ZIP average.

Recent from the blog

Posts are coming soon. Planned: "Are frost dates shifting? 1991–2020 vs 1981–2010", "Reading chill hours for fruit trees".

Blog →

Questions about 91942

What USDA hardiness zone is 91942?

ZIP 91942 (La Mesa, CA) is in USDA zone 10b (35 to 40°F average annual extreme minimum), per the 2023 USDA Plant Hardiness Zone Map.

When is the last frost in 91942?

Based on NOAA 1991–2020 normals at Ca El Cajon (8.7 km away), the median last 32°F freeze is Jan 6. In 1 of 10 years it is after Feb 7. The median first fall freeze is Dec 21.

Nearby ZIP codes

91941 La Mesa 92119 San Diego 92182 San Diego 92115 San Diego 91945 Lemon Grove 92020 El Cajon

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 EL CAJON (USC00042706) 8.7 km away 27 yrs of record · 85 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/91942.json

Garden Climate for El Cajon, La Mesa, Lakeside area: 91942, 91978, 92019, 92020, 92021, 92040, 92071, 92119

ZIPs in this area

USDA Plant Hardiness Zone Map · La Mesa focus

Frost dates for 91942

Newsletter · 91942

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

What to grow when · 91942

Questions about 91942

Nearby ZIP codes

Sources for this page