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

Planting zone for 93099 — Simi Valley, CA

ZIP code 93099 (Simi Valley, Ventura County) is in USDA zone 10a: the coldest winter night averages 30 to 35 °F. The median last spring frost is January 24 and the first fall frost December 15.

Where ZIP 93099 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.

Zone10a30 to 35 °F
Coldest night−1.1 to 1.7 °C
Last frostJan 24
First frostDec 15
2012 zone10a

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 10a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Simi Valley, 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 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 — 13 miles away, 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 93099

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 93099 came on Jan 16 — 6 days earlier than the 1991–2020 average (Jan 22).

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 93099 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 93099; 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

30°40°50°60°70°80°90°100°110°32 °FJanuary: average high 70 °F, low 43 °F 70°43° JanFebruary: average high 70 °F, low 44 °F 70°44° FebMarch: average high 74 °F, low 46 °F 74°46° MarApril: average high 78 °F, low 48 °F 78°48° AprMay: average high 82 °F, low 53 °F 82°53° MayJune: average high 89 °F, low 57 °F 89°57° JunJuly: average high 95 °F, low 61 °F 95°61° JulAugust: average high 97 °F, low 61 °F 97°61° AugSeptember: average high 94 °F, low 59 °F 94°59° SepOctober: average high 85 °F, low 53 °F 85°53° OctNovember: average high 76 °F, low 46 °F 76°46° NovDecember: average high 69 °F, low 42 °F 69°42° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 3.73 in precipitation 3.7 JanFebruary: 4.14 in precipitation 4.1 FebMarch: 2.58 in precipitation 2.6 MarApril: 0.79 in precipitation 0.8 AprMay: 0.36 in precipitation 0.4 MayJune: 0.08 in precipitation 0.1 JunJuly: 0.05 in precipitation 0.1 JulAugust: 0.01 in precipitation 0.0 AugSeptember: 0.10 in precipitation 0.1 SepOctober: 0.74 in precipitation 0.7 OctNovember: 0.92 in precipitation 0.9 NovDecember: 2.60 in precipitation 2.6 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Woodland Hills Pierce College, CA (13 mi away); precipitation: Thousand Oaks 2.1 Wsw, CA (9 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

9306210a
Simi Valley, CA · <1 mi
9309410a
Simi Valley, CA · <1 mi
9306510a
Simi Valley, CA · <1 mi
9306410a
Brandeis, CA · 5 mi
9136210b
Thousand Oaks, CA · 6 mi
9302010a
Moorpark, CA · 6 mi
9137710b
Oak Park, CA · 6 mi
9306310a
Simi Valley, CA · 6 mi

All 5 ZIP codes in Simi Valley → · California planting zones →

Questions about 93099

What planting zone is ZIP code 93099?

ZIP code 93099 (Simi Valley, 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 Simi Valley, CA?

The median last spring frost (32 °F) near 93099 is January 24; after March 5 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Woodland Hills Pierce College station.

When is the first frost in Simi Valley, CA?

The median first fall frost near 93099 is December 15, giving a median frost-free growing season of 329 days.

When should I plant tomatoes in 93099?

Start tomato seeds indoors around Nov 29 – Dec 13 and set transplants outside around Jan 31 – Feb 14, one to three weeks after the median last frost.

How much rain and snow does 93099 get?

About 16.1 inches of precipitation a year (NOAA 1991–2020 normals, Thousand Oaks 2.1 Wsw station).

How hot do summers get in Simi Valley, CA?

The average high peaks at 97 °F in August, with about 115 days a year at 90 °F or more.

What kind of soil does 93099 have?

The USDA soil survey maps Mocho at the center of ZIP 93099: loam, well drained, pH about 8.0 (alkaline).

Did spring come early in Simi Valley, CA in 2026?

Spring leaf-out near 93099 came on Jan 16 in 2026, 6 days earlier than the 1991–2020 average (Jan 22), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Simi Valley, CA?

Intermediate onions: the longest day near 93099 is 14 h 27 min, so day-neutral types bulb best; long-day varieties may not bulb fully.