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

Planting zone for 91963 — Potrero, CA

ZIP code 91963 (Potrero, San Diego County) is in USDA zone 9a: the coldest winter night averages 20 to 25 °F. The median last spring frost is April 30 and the first fall frost October 26.

Where ZIP 91963 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.

Zone9a20 to 25 °F
Coldest night−6.7 to −3.9 °C
Last frostApr 30
First frostOct 26
2012 zone9a

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 9a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Potrero, 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 Potrero, CA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 30median — 50% chance of a later frost
Safe for tender plantsJune 1only 10% chance of frost after
First fall frostOctober 26median — 10% chance by Sep 30
Growing season174 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 2 and returns around November 14.

From the NOAA station Campo, CA — 7 miles away, elevation 2,631 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 91963

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 19 – Apr 2
SpinachSow outdoors · Mar 19 – Apr 9
Broccoli, cabbageStart indoors · Feb 19 – Mar 5
Broccoli, cabbageTransplant · Apr 9 – Apr 23
Onion setsPlant outdoors · Apr 2 – Apr 16
PotatoesPlant outdoors · Apr 9 – Apr 23
LettuceSow outdoors · Apr 2 – Apr 16
Carrots, beetsSow outdoors · Apr 9 – Apr 23
TomatoesStart indoors · Mar 5 – Mar 19
TomatoesTransplant · May 7 – May 21
Peppers, eggplantStart indoors · Feb 19 – Mar 5
Peppers, eggplantTransplant · May 14 – May 28
BeansSow outdoors · May 7 – May 21
Sweet cornSow outdoors · May 7 – May 21
Cucumbers, squashSow outdoors · May 7 – May 21
Fall lettuce, spinachSow outdoors · Aug 31 – Sep 14
GarlicPlant cloves · Oct 12 – Nov 16
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 30) and first fall frost (Oct 26) 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 91963 came on Jan 19 — 10 days earlier than the 1991–2020 average (Jan 29).

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 Potrero, CA

The soil mapped at the center of ZIP 91963 is La Posta — loamy coarse sand, somewhat excessively drained.

TextureLoamy coarse sanddrains and warms fast; dries out and needs more feeding
pH6.7neutral; most vegetables like 6.0–7.0
DrainageSomewhat excessively drainednatural drainage class
Organic matter2%moderate
Hydrologic groupAwater soaks in fast
Farmland classNot prime farmlandUSDA classification

Map unit: La Posta rocky loamy coarse sand, 5 to 30 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 91963; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Potrero, CA

Summer high95 °Faverage high, August
Winter low33 °Faverage low, December
Hot days97days a year at 90 °F or more
Freezing nights71nights a year at 32 °F or less
Growing degree days3,872base 50 °F — the season’s usable heat
Longest day14 h 18 mindaylight on June 21
Shortest day10 h 00 mindaylight on December 21
Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully
Precipitation15.6 inper year, rain and melted snow

Average high and low, by month

20°30°40°50°60°70°80°90°100°110°32 °FJanuary: average high 64 °F, low 35 °F 64°35° JanFebruary: average high 64 °F, low 35 °F 64°35° FebMarch: average high 68 °F, low 36 °F 68°36° MarApril: average high 73 °F, low 38 °F 73°38° AprMay: average high 79 °F, low 42 °F 79°42° MayJune: average high 88 °F, low 45 °F 88°45° JunJuly: average high 94 °F, low 53 °F 94°53° JulAugust: average high 95 °F, low 54 °F 95°54° AugSeptember: average high 90 °F, low 50 °F 90°50° SepOctober: average high 80 °F, low 43 °F 80°43° OctNovember: average high 71 °F, low 37 °F 71°37° NovDecember: average high 63 °F, low 33 °F 63°33° Dec

Precipitation by month inches

0″1″2″3″4″January: 3.09 in precipitation, 0.1 in snowfall 3.1 JanFebruary: 3.45 in precipitation 3.5 FebMarch: 2.28 in precipitation 2.3 MarApril: 1.04 in precipitation, 0.1 in snowfall 1.0 AprMay: 0.38 in precipitation 0.4 MayJune: 0.09 in precipitation 0.1 JunJuly: 0.29 in precipitation 0.3 JulAugust: 0.42 in precipitation 0.4 AugSeptember: 0.40 in precipitation 0.4 SepOctober: 0.67 in precipitation 0.7 OctNovember: 1.03 in precipitation 1.0 NovDecember: 2.44 in precipitation, 0.1 in snowfall 2.4 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Campo, CA (7 mi away); precipitation: Campo, CA (7 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.

919809b
Tecate, CA · 5 mi
919879b
Tecate, CA · 5 mi
919069a
Campo, CA · 7 mi
9191710a
Dulzura, CA · 9 mi
9193510a
Jamul, CA · 11 mi
919318b
Guatay, CA · 13 mi
919019b
Alpine, CA · 14 mi
919628b
Pine Valley, CA · 14 mi

California planting zones →

Questions about 91963

What planting zone is ZIP code 91963?

ZIP code 91963 (Potrero, CA) is in USDA hardiness zone 9a on the 2023 map: the coldest night of an average winter reaches 20 to 25 °F (−6.7 to −3.9 °C).

When is the last frost in Potrero, CA?

The median last spring frost (32 °F) near 91963 is April 30; after June 1 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Campo station.

When is the first frost in Potrero, CA?

The median first fall frost near 91963 is October 26, giving a median frost-free growing season of 174 days.

When should I plant tomatoes in 91963?

Start tomato seeds indoors around Mar 5 – Mar 19 and set transplants outside around May 7 – May 21, one to three weeks after the median last frost.

How much rain and snow does 91963 get?

About 15.6 inches of precipitation a year (NOAA 1991–2020 normals, Campo station).

How hot do summers get in Potrero, CA?

The average high peaks at 95 °F in August, with about 97 days a year at 90 °F or more.

What kind of soil does 91963 have?

The USDA soil survey maps La Posta at the center of ZIP 91963: loamy coarse sand, somewhat excessively drained, pH about 6.7 (neutral).

Did spring come early in Potrero, CA in 2026?

Spring leaf-out near 91963 came on Jan 19 in 2026, 10 days earlier than the 1991–2020 average (Jan 29), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Potrero, CA?

Intermediate onions: the longest day near 91963 is 14 h 18 min, so day-neutral types bulb best; long-day varieties may not bulb fully.