Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 29, 2026

Planting zone for Simi Valley, CA

Simi Valley, CA is in USDA zone 10a across its 5 ZIP codes. The median last spring frost is January 24 and the first fall frost December 15.

Simi Valley on the zone map

Outlined: its 2 ZIP code areas · 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

ZIP codes5

Last frostJan 24

First frostDec 15

Growing season329 days

10a 5 ZIPs

Frost forecast — next 7 nights

live from the National Weather Service

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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 Simi Valley, CA

JanFebMarAprMayJunJulAugSepOctNovDec

Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free

Last spring frostJanuary 24median — 50% chance of a later frost

Safe for tender plantsMarch 5only 10% chance of frost after

First fall frostDecember 15median — 10% chance by Nov 27

Growing season329 daysfrost-free, median

A hard freeze (28 °F) usually ends around December 31 and returns around December 26.

From the NOAA station Woodland Hills Pierce College, CA, elevation 791 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 Simi Valley

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Dec 13 – Dec 27

SpinachSow outdoors · Dec 13 – Jan 3

Broccoli, cabbageStart indoors · Nov 15 – Nov 29

Broccoli, cabbageTransplant · Jan 3 – Jan 17

Onion setsPlant outdoors · Dec 27 – Jan 10

PotatoesPlant outdoors · Jan 3 – Jan 17

LettuceSow outdoors · Dec 27 – Jan 10

Carrots, beetsSow outdoors · Jan 3 – Jan 17

TomatoesStart indoors · Nov 29 – Dec 13

TomatoesTransplant · Jan 31 – Feb 14

Peppers, eggplantStart indoors · Nov 15 – Nov 29

Peppers, eggplantTransplant · Feb 7 – Feb 21

BeansSow outdoors · Jan 31 – Feb 14

Sweet cornSow outdoors · Jan 31 – Feb 14

Cucumbers, squashSow outdoors · Jan 31 – Feb 14

Fall lettuce, spinachSow outdoors · Oct 20 – Nov 3

GarlicPlant cloves · Dec 1 – Jan 5

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jan 24) and first fall frost (Dec 15) 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 93065 came on Jan 16 — 6 days earlier than the 1991–2020 average (Jan 22).

average
Jan 222026
Jan 16

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 Simi Valley, CA

The soil mapped at the center of ZIP 93065 is Mocho — loam, well drained.

TextureLoama good balance for most vegetables

pH8.0alkaline; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter3%moderate

Hydrologic groupBwater soaks in moderately

Farmland classPrime farmland if irrigatedUSDA classification

Map unit: Mocho loam, 0 to 2 percent slopes, warm MAAT, MLRA 19.

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 93065; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Simi Valley, CA

Summer high97 °Faverage high, August

Winter low42 °Faverage low, December

Hot days115days a year at 90 °F or more

Freezing nights11nights a year at 32 °F or less

Growing degree days6,002base 50 °F — the season’s usable heat

Longest day14 h 27 mindaylight on June 21

Shortest day9 h 52 mindaylight on December 21

Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully

Precipitation16.1 inper year, rain and melted snow

Average high and low, by month

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Woodland Hills Pierce College, CA (12 mi away); precipitation: Thousand Oaks 2.1 Wsw, CA (9 mi away). Daylight is calculated from latitude.

ZIP codes in Simi Valley

California planting zones →

Questions about Simi Valley

What planting zone is Simi Valley, CA?

Simi Valley, CA is in USDA hardiness zone 10a on the 2023 map (10a: 30 to 35 °F).

When is the last frost in Simi Valley, CA?

The median last spring frost is January 24 and the median first fall frost is December 15 (NOAA 1991–2020 normals, Woodland Hills Pierce College station).

When can I plant a garden in Simi Valley, CA?

Cool-season crops like peas and spinach go in around Dec 13 – Jan 3; tomatoes, peppers, beans and squash after about Jan 31, once frost risk has passed.

What kind of onions grow in Simi Valley, CA?

Intermediate onions: the longest day is 14 h 27 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

How much rain and snow does Simi Valley, CA get?

About 16.1 inches of precipitation a year (NOAA 1991–2020 normals).