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

Planting zone for 91917 — Dulzura, CA

ZIP code 91917 (Dulzura, San Diego County) is in USDA zone 10a: the coldest winter night averages 30 to 35 °F. The median last spring frost is February 12 and the first fall frost December 24.

Where ZIP 91917 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.

Zone10a30 to 35 °F
Coldest night−1.1 to 1.7 °C
Last frostFeb 12
First frostDec 24
2012 zone9b

Was 9b 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 10a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Dulzura, 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 Dulzura, CA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostFebruary 12median — 50% chance of a later frost
Safe for tender plantsMarch 20only 10% chance of frost after
First fall frostDecember 24median — 10% chance by Dec 2
Growing season317 daysfrost-free, median

A hard freeze (28 °F) usually ends around January 22 and returns around January 4.

From the NOAA station Alpine, CA — 14 miles away, elevation 1,696 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 91917

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Jan 1 – Jan 15
SpinachSow outdoors · Jan 1 – Jan 22
Broccoli, cabbageStart indoors · Dec 4 – Dec 18
Broccoli, cabbageTransplant · Jan 22 – Feb 5
Onion setsPlant outdoors · Jan 15 – Jan 29
PotatoesPlant outdoors · Jan 22 – Feb 5
LettuceSow outdoors · Jan 15 – Jan 29
Carrots, beetsSow outdoors · Jan 22 – Feb 5
TomatoesStart indoors · Dec 18 – Jan 1
TomatoesTransplant · Feb 19 – Mar 5
Peppers, eggplantStart indoors · Dec 4 – Dec 18
Peppers, eggplantTransplant · Feb 26 – Mar 12
BeansSow outdoors · Feb 19 – Mar 5
Sweet cornSow outdoors · Feb 19 – Mar 5
Cucumbers, squashSow outdoors · Feb 19 – Mar 5
Fall lettuce, spinachSow outdoors · Oct 29 – Nov 12
GarlicPlant cloves · Dec 10 – Jan 14
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Feb 12) and first fall frost (Dec 24) 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 91917 came on Jan 17 — 9 days earlier than the 1991–2020 average (Jan 26).

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 Dulzura, CA

The soil mapped at the center of ZIP 91917 is Friant — fine sandy loam, well drained.

TextureFine sandy loamdrains and warms fast; dries out and needs more feeding
pH6.3slightly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter1.5%low — add compost
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Friant rocky fine sandy loam, 30 to 70 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 91917; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Dulzura, CA

Summer high89 °Faverage high, August
Winter low42 °Faverage low, February
Hot days55days a year at 90 °F or more
Freezing nights3nights a year at 32 °F or less
Growing degree days4,757base 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 growShort-daysummer days stay under about 14 h 20 min, so long-day varieties won’t bulb
Precipitation12.2 inper year, rain and melted snow

Average high and low, by month

30°40°50°60°70°80°90°100°32 °FJanuary: average high 64 °F, low 43 °F 64°43° JanFebruary: average high 64 °F, low 42 °F 64°42° FebMarch: average high 67 °F, low 44 °F 67°44° MarApril: average high 71 °F, low 47 °F 71°47° AprMay: average high 74 °F, low 51 °F 74°51° MayJune: average high 81 °F, low 54 °F 81°54° JunJuly: average high 87 °F, low 60 °F 87°60° JulAugust: average high 89 °F, low 62 °F 89°62° AugSeptember: average high 86 °F, low 60 °F 86°60° SepOctober: average high 78 °F, low 54 °F 78°54° OctNovember: average high 71 °F, low 48 °F 71°48° NovDecember: average high 63 °F, low 42 °F 63°42° Dec

Precipitation by month inches

0″1″2″3″January: 2.57 in precipitation 2.6 JanFebruary: 2.87 in precipitation 2.9 FebMarch: 1.85 in precipitation 1.9 MarApril: 0.79 in precipitation 0.8 AprMay: 0.37 in precipitation 0.4 MayJune: 0.08 in precipitation 0.1 JunJuly: 0.08 in precipitation 0.1 JulAugust: 0.03 in precipitation 0.0 AugSeptember: 0.17 in precipitation 0.2 SepOctober: 0.52 in precipitation 0.5 OctNovember: 1.04 in precipitation 1.0 NovDecember: 1.82 in precipitation 1.8 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Alpine, CA (14 mi away); precipitation: Chula Vista 6.3e, CA (13 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.

9193510a
Jamul, CA · 4 mi
919809b
Tecate, CA · 8 mi
919879b
Tecate, CA · 9 mi
919639a
Potrero, CA · 9 mi
9197810b
Spring Valley, CA · 11 mi
9217910b
San Diego, CA · 11 mi
9191510b
Chula Vista, CA · 11 mi
9201910b
El Cajon, CA · 12 mi

California planting zones →

Questions about 91917

What planting zone is ZIP code 91917?

ZIP code 91917 (Dulzura, CA) is in USDA hardiness zone 10a on the 2023 map: the coldest night of an average winter reaches 30 to 35 °F (−1.1 to 1.7 °C).

When is the last frost in Dulzura, CA?

The median last spring frost (32 °F) near 91917 is February 12; after March 20 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Alpine station.

When is the first frost in Dulzura, CA?

The median first fall frost near 91917 is December 24, giving a median frost-free growing season of 317 days.

When should I plant tomatoes in 91917?

Start tomato seeds indoors around Dec 18 – Jan 1 and set transplants outside around Feb 19 – Mar 5, one to three weeks after the median last frost.

How much rain and snow does 91917 get?

About 12.2 inches of precipitation a year (NOAA 1991–2020 normals, Chula Vista 6.3e station).

How hot do summers get in Dulzura, CA?

The average high peaks at 89 °F in August, with about 55 days a year at 90 °F or more.

What kind of soil does 91917 have?

The USDA soil survey maps Friant at the center of ZIP 91917: fine sandy loam, well drained, pH about 6.3 (slightly acidic).

Did spring come early in Dulzura, CA in 2026?

Spring leaf-out near 91917 came on Jan 17 in 2026, 9 days earlier than the 1991–2020 average (Jan 26), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Dulzura, CA?

Short-day onions: the longest day near 91917 is 14 h 18 min, so summer days stay under about 14 h 20 min, so long-day varieties won’t bulb.

Did the zone for 91917 change?

Yes. The 2012 USDA map put 91917 in zone 9b; the 2023 map puts it in zone 10a. The newer map uses 1991–2020 data and more weather stations.