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

Planting zone for 91943 — La Mesa, CA

ZIP code 91943 (La Mesa, San Diego County) is in USDA zone 10b: the coldest winter night averages 35 to 40 °F.

Where ZIP 91943 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.

Zone10b35 to 40 °F
Coldest night1.7 to 4.4 °C
Last frostrare
First frostrare
2012 zone10a

Was 10a on the 2012 map — half a zone warmer now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 10b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for La Mesa, 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 El Cajon, CA — 6 miles away, elevation 495 ft) the median growing season is 350 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 91943 came on Jan 17 — 4 days earlier than the 1991–2020 average (Jan 21).

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 La Mesa, CA

The soil mapped at the center of ZIP 91943 is Redding — gravelly loam, well drained.

TextureGravelly loama good balance for most vegetables
pH5.6moderately acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter1.25%low — add compost
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Redding-Urban land complex, 2 to 9 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 91943; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in La Mesa, CA

Summer high89 °Faverage high, August
Winter low42 °Faverage low, December
Hot days57days a year at 90 °F or more
Freezing nights3nights a year at 32 °F or less
Growing degree days5,564base 50 °F — the season’s usable heat
Longest day14 h 19 mindaylight on June 21
Shortest day9 h 59 mindaylight on December 21
Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully
Precipitation12 inper year, rain and melted snow

Average high and low, by month

30°40°50°60°70°80°90°100°32 °FJanuary: average high 69 °F, low 43 °F 69°43° JanFebruary: average high 69 °F, low 44 °F 69°44° FebMarch: average high 71 °F, low 48 °F 71°48° MarApril: average high 75 °F, low 51 °F 75°51° AprMay: average high 76 °F, low 56 °F 76°56° MayJune: average high 81 °F, low 59 °F 81°59° JunJuly: average high 86 °F, low 63 °F 86°63° JulAugust: average high 89 °F, low 65 °F 89°65° AugSeptember: average high 87 °F, low 62 °F 87°62° SepOctober: average high 81 °F, low 56 °F 81°56° OctNovember: average high 75 °F, low 47 °F 75°47° NovDecember: average high 69 °F, low 42 °F 69°42° Dec

Precipitation by month inches

0″1″2″3″January: 2.62 in precipitation 2.6 JanFebruary: 2.83 in precipitation 2.8 FebMarch: 1.79 in precipitation 1.8 MarApril: 0.68 in precipitation 0.7 AprMay: 0.29 in precipitation 0.3 MayJune: 0.07 in precipitation 0.1 JunJuly: 0.11 in precipitation 0.1 JulAugust: 0.04 in precipitation 0.0 AugSeptember: 0.19 in precipitation 0.2 SepOctober: 0.57 in precipitation 0.6 OctNovember: 0.87 in precipitation 0.9 NovDecember: 1.90 in precipitation 1.9 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: El Cajon, CA (6 mi away); precipitation: La Mesa 0.9 Sw, CA (within 1 mile). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 10b.

9194410b
La Mesa, CA · <1 mi
9194210b
La Mesa, CA · <1 mi
9194110b
La Mesa, CA · 2 mi
9194610b
Lemon Grove, CA · 2 mi
9197610b
Spring Valley, CA · 2 mi
9197910b
Spring Valley, CA · 2 mi
9194510b
Lemon Grove, CA · 2 mi
9211510b
San Diego, CA · 3 mi

All 4 ZIP codes in La Mesa → · California planting zones →

Questions about 91943

What planting zone is ZIP code 91943?

ZIP code 91943 (La Mesa, CA) is in USDA hardiness zone 10b on the 2023 map: the coldest night of an average winter reaches 35 to 40 °F (1.7 to 4.4 °C).

How much rain and snow does 91943 get?

About 12 inches of precipitation a year (NOAA 1991–2020 normals, La Mesa 0.9 Sw station).

How hot do summers get in La Mesa, CA?

The average high peaks at 89 °F in August, with about 57 days a year at 90 °F or more.

What kind of soil does 91943 have?

The USDA soil survey maps Redding at the center of ZIP 91943: gravelly loam, well drained, pH about 5.6 (moderately acidic).

Did spring come early in La Mesa, CA in 2026?

Spring leaf-out near 91943 came on Jan 17 in 2026, 4 days earlier than the 1991–2020 average (Jan 21), according to the USA National Phenology Network Spring Index.

What kind of onions grow in La Mesa, CA?

Intermediate onions: the longest day near 91943 is 14 h 19 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 91943 change?

Yes. The 2012 USDA map put 91943 in zone 10a; the 2023 map puts it in zone 10b. The newer map uses 1991–2020 data and more weather stations.