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

Planting zone for 91931 — Guatay, CA

ZIP code 91931 (Guatay, San Diego County) is in USDA zone 8b: the coldest winter night averages 15 to 20 °F. The median last spring frost is April 22 and the first fall frost November 8.

Where ZIP 91931 is

Outlined: the ZIP code area · 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.

Zone8b15 to 20 °F
Coldest night−9.4 to −6.7 °C
Last frostApr 22
First frostNov 8
2012 zone8b

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 8b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Guatay, 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 in Guatay, CA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 22median — 50% chance of a later frost
Safe for tender plantsMay 21only 10% chance of frost after
First fall frostNovember 8median — 10% chance by Oct 10
Growing season197 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 2 and returns around December 1.

From the NOAA station Mt Laguna #3, CA — 9 miles away, elevation 5,919 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 91931

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 11 – Mar 25
SpinachSow outdoors · Mar 11 – Apr 1
Broccoli, cabbageStart indoors · Feb 11 – Feb 25
Broccoli, cabbageTransplant · Apr 1 – Apr 15
Onion setsPlant outdoors · Mar 25 – Apr 8
PotatoesPlant outdoors · Apr 1 – Apr 15
LettuceSow outdoors · Mar 25 – Apr 8
Carrots, beetsSow outdoors · Apr 1 – Apr 15
TomatoesStart indoors · Feb 25 – Mar 11
TomatoesTransplant · Apr 29 – May 13
Peppers, eggplantStart indoors · Feb 11 – Feb 25
Peppers, eggplantTransplant · May 6 – May 20
BeansSow outdoors · Apr 29 – May 13
Sweet cornSow outdoors · Apr 29 – May 13
Cucumbers, squashSow outdoors · Apr 29 – May 13
Fall lettuce, spinachSow outdoors · Sep 13 – Sep 27
GarlicPlant cloves · Oct 25 – Nov 29
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 22) and first fall frost (Nov 8) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 91931 came on Jan 23 — 12 days earlier than the 1991–2020 average (Feb 4).

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 Guatay, CA

The soil mapped at the center of ZIP 91931 is Las Posas — loam, well drained.

TextureLoama good balance for most vegetables
pH6.2slightly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter1.2%low — add compost
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Las Posas loam, 30 to 65 percent slopes, stony.

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 91931; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Guatay, CA

Summer high83 °Faverage high, July
Winter low33 °Faverage low, January
Hot days4days a year at 90 °F or more
Freezing nights63nights a year at 32 °F or less
Growing degree days2,908base 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
Precipitation22.5 inper year, rain and melted snow

Average high and low, by month

20°30°40°50°60°70°80°90°32 °FJanuary: average high 50 °F, low 33 °F 50°33° JanFebruary: average high 50 °F, low 34 °F 50°34° FebMarch: average high 54 °F, low 36 °F 54°36° MarApril: average high 61 °F, low 40 °F 61°40° AprMay: average high 68 °F, low 46 °F 68°46° MayJune: average high 78 °F, low 53 °F 78°53° JunJuly: average high 83 °F, low 60 °F 83°60° JulAugust: average high 82 °F, low 58 °F 82°58° AugSeptember: average high 76 °F, low 54 °F 76°54° SepOctober: average high 67 °F, low 45 °F 67°45° OctNovember: average high 57 °F, low 38 °F 57°38° NovDecember: average high 51 °F, low 34 °F 51°34° Dec

Precipitation by month inches

0″1″2″3″4″5″6″January: 3.91 in precipitation 3.9 JanFebruary: 5.12 in precipitation 5.1 FebMarch: 3.77 in precipitation 3.8 MarApril: 1.68 in precipitation 1.7 AprMay: 0.64 in precipitation 0.6 MayJune: 0.10 in precipitation 0.1 JunJuly: 0.34 in precipitation 0.3 JulAugust: 0.29 in precipitation 0.3 AugSeptember: 0.42 in precipitation 0.4 SepOctober: 0.80 in precipitation 0.8 OctNovember: 1.93 in precipitation 1.9 NovDecember: 3.52 in precipitation 3.5 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Mt Laguna #3, CA (9 mi away); precipitation: Descanso 0.3 Wnw, CA (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

919628b
Pine Valley, CA · 4 mi
919169b
Descanso, CA · 6 mi
919488a
Mount Laguna, CA · 7 mi
919019b
Alpine, CA · 9 mi
919039b
Alpine, CA · 11 mi
919639a
Potrero, CA · 13 mi
919069a
Campo, CA · 14 mi
9193510a
Jamul, CA · 15 mi

California planting zones →

Questions about 91931

What planting zone is ZIP code 91931?

ZIP code 91931 (Guatay, CA) is in USDA hardiness zone 8b on the 2023 map: the coldest night of an average winter reaches 15 to 20 °F (−9.4 to −6.7 °C).

When is the last frost in Guatay, CA?

The median last spring frost (32 °F) near 91931 is April 22; after May 21 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Mt Laguna #3 station.

When is the first frost in Guatay, CA?

The median first fall frost near 91931 is November 8, giving a median frost-free growing season of 197 days.

When should I plant tomatoes in 91931?

Start tomato seeds indoors around Feb 25 – Mar 11 and set transplants outside around Apr 29 – May 13, one to three weeks after the median last frost.

How much rain and snow does 91931 get?

About 22.5 inches of precipitation a year (NOAA 1991–2020 normals, Descanso 0.3 Wnw station).

How hot do summers get in Guatay, CA?

The average high peaks at 83 °F in July, with about 4 days a year at 90 °F or more.

What kind of soil does 91931 have?

The USDA soil survey maps Las Posas at the center of ZIP 91931: loam, well drained, pH about 6.2 (slightly acidic).

Did spring come early in Guatay, CA in 2026?

Spring leaf-out near 91931 came on Jan 23 in 2026, 12 days earlier than the 1991–2020 average (Feb 4), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Guatay, CA?

Intermediate onions: the longest day near 91931 is 14 h 19 min, so day-neutral types bulb best; long-day varieties may not bulb fully.