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

Planting zone for 93420 — Arroyo Grande, CA

ZIP code 93420 (Arroyo Grande, San Luis Obispo County) is in USDA zone 9b: the coldest winter night averages 25 to 30 °F. The median last spring frost is January 31 and the first fall frost December 11.

Where ZIP 93420 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.

Zone9b25 to 30 °F
Coldest night−3.9 to −1.1 °C
Last frostJan 31
First frostDec 11
2012 zone9b

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 9b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Arroyo Grande, 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 Arroyo Grande, CA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostJanuary 31median — 50% chance of a later frost
Safe for tender plantsMarch 7only 10% chance of frost after
First fall frostDecember 11median — 10% chance by Nov 20
Growing season319 daysfrost-free, median

A hard freeze (28 °F) usually ends around January 3 and returns around December 28.

From the NOAA station San Luis Obispo Airport, CA — 10 miles away, elevation 200 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 93420

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Dec 20 – Jan 3
SpinachSow outdoors · Dec 20 – Jan 10
Broccoli, cabbageStart indoors · Nov 22 – Dec 6
Broccoli, cabbageTransplant · Jan 10 – Jan 24
Onion setsPlant outdoors · Jan 3 – Jan 17
PotatoesPlant outdoors · Jan 10 – Jan 24
LettuceSow outdoors · Jan 3 – Jan 17
Carrots, beetsSow outdoors · Jan 10 – Jan 24
TomatoesStart indoors · Dec 6 – Dec 20
TomatoesTransplant · Feb 7 – Feb 21
Peppers, eggplantStart indoors · Nov 22 – Dec 6
Peppers, eggplantTransplant · Feb 14 – Feb 28
BeansSow outdoors · Feb 7 – Feb 21
Sweet cornSow outdoors · Feb 7 – Feb 21
Cucumbers, squashSow outdoors · Feb 7 – Feb 21
Fall lettuce, spinachSow outdoors · Oct 16 – Oct 30
GarlicPlant cloves · Nov 27 – Jan 1
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jan 31) and first fall frost (Dec 11) 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 93420 came on Jan 19 — 7 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 Arroyo Grande, CA

The soil mapped at the center of ZIP 93420 is Salinas — silty clay loam, well drained.

TextureSilty clay loamholds water and nutrients; slow to drain and warm up
pH8.2alkaline; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter2.5%moderate
Hydrologic groupCwater soaks in slowly
Farmland classPrime farmland if irrigatedUSDA classification

Map unit: Salinas silty clay loam, 2 to 9 percent slopes, MLRA 14.

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 93420; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Arroyo Grande, CA

Summer high80 °Faverage high, September
Winter low40 °Faverage low, December
Hot days15days a year at 90 °F or more
Freezing nights8nights a year at 32 °F or less
Growing degree days3,646base 50 °F — the season’s usable heat
Longest day14 h 32 mindaylight on June 21
Shortest day9 h 47 mindaylight on December 21
Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully
Precipitation17.9 inper year, rain and melted snow

Average high and low, by month

30°40°50°60°70°80°90°32 °FJanuary: average high 65 °F, low 41 °F 65°41° JanFebruary: average high 65 °F, low 42 °F 65°42° FebMarch: average high 67 °F, low 45 °F 67°45° MarApril: average high 69 °F, low 46 °F 69°46° AprMay: average high 72 °F, low 48 °F 72°48° MayJune: average high 75 °F, low 51 °F 75°51° JunJuly: average high 78 °F, low 54 °F 78°54° JulAugust: average high 79 °F, low 55 °F 79°55° AugSeptember: average high 80 °F, low 53 °F 80°53° SepOctober: average high 77 °F, low 50 °F 77°50° OctNovember: average high 71 °F, low 45 °F 71°45° NovDecember: average high 65 °F, low 40 °F 65°40° Dec

Precipitation by month inches

0″1″2″3″4″January: 3.86 in precipitation 3.9 JanFebruary: 3.54 in precipitation 3.5 FebMarch: 3.17 in precipitation 3.2 MarApril: 1.05 in precipitation 1.1 AprMay: 0.47 in precipitation 0.5 MayJune: 0.10 in precipitation 0.1 JunJuly: 0.08 in precipitation 0.1 JulAugust: 0.01 in precipitation 0.0 AugSeptember: 0.04 in precipitation 0.0 SepOctober: 0.92 in precipitation 0.9 OctNovember: 1.43 in precipitation 1.4 NovDecember: 3.27 in precipitation 3.3 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: San Luis Obispo Airport, CA (10 mi away); precipitation: San Luis Obispo Airport, CA (10 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

934019b
San Luis Obispo, CA · 9 mi
9343310a
Grover Beach, CA · 9 mi
9348310a
Grover Beach, CA · 9 mi
9347510a
Oceano, CA · 9 mi
9344810a
Pismo Beach, CA · 10 mi
934449b
Nipomo, CA · 10 mi
9344910a
Pismo Beach, CA · 10 mi
9344510a
Oceano, CA · 12 mi

California planting zones →

Questions about 93420

What planting zone is ZIP code 93420?

ZIP code 93420 (Arroyo Grande, CA) is in USDA hardiness zone 9b on the 2023 map: the coldest night of an average winter reaches 25 to 30 °F (−3.9 to −1.1 °C).

When is the last frost in Arroyo Grande, CA?

The median last spring frost (32 °F) near 93420 is January 31; after March 7 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, San Luis Obispo Airport station.

When is the first frost in Arroyo Grande, CA?

The median first fall frost near 93420 is December 11, giving a median frost-free growing season of 319 days.

When should I plant tomatoes in 93420?

Start tomato seeds indoors around Dec 6 – Dec 20 and set transplants outside around Feb 7 – Feb 21, one to three weeks after the median last frost.

How much rain and snow does 93420 get?

About 17.9 inches of precipitation a year (NOAA 1991–2020 normals, San Luis Obispo Airport station).

How hot do summers get in Arroyo Grande, CA?

The average high peaks at 80 °F in September, with about 15 days a year at 90 °F or more.

What kind of soil does 93420 have?

The USDA soil survey maps Salinas at the center of ZIP 93420: silty clay loam, well drained, pH about 8.2 (alkaline).

Did spring come early in Arroyo Grande, CA in 2026?

Spring leaf-out near 93420 came on Jan 19 in 2026, 7 days earlier than the 1991–2020 average (Jan 26), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Arroyo Grande, CA?

Intermediate onions: the longest day near 93420 is 14 h 32 min, so day-neutral types bulb best; long-day varieties may not bulb fully.