When is the last frost in San Luis Obispo, CA?

The average last spring frost (50% probability of 32°F) in San Luis Obispo is around January 16, based on NOAA/NCEI 1991–2020 normals at the San Luis Obispo Poly, CA station (4.1 mi away). Half of years it falls outside that date, so wait 1–2 weeks past it before setting out frost-tender plants.

When is the first fall frost in San Luis Obispo?

The average first fall frost in San Luis Obispo, CA is around December 25, giving roughly a 349-day frost-free growing season.

What planting zone is San Luis Obispo, CA?

San Luis Obispo is in USDA plant hardiness zone 9b (average annual extreme minimum temperature 25 to 30°F), from the 2023 USDA Plant Hardiness Zone Map.

What is the weather like in San Luis Obispo?

In San Luis Obispo, CA the warmest month is September (avg high 80.1°F) and the coldest is December (avg low 43.7°F). It averages about 22.4″ of precipitation a year.

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San Luis Obispo, CA Planting Calendar & Frost Dates

USDA hardiness zone 9b · ZIP 93405 · elevation 94′ · NOAA & USDA data

San Luis Obispo is in USDA hardiness zone 9b (winters can dip to 25 to 30°F), with a growing season of about 349 days between the average last spring frost (January 16) and first fall frost (December 25). The warmest month is September (avg high 80.1°F); the coldest is December (avg low 43.7°F). It averages 22.4″ of precipitation a year. Start cool-season crops several weeks before the last frost; wait until after it for tomatoes, peppers and other tender crops.

Hardiness zone

min temp 25 to 30°F

Last spring frost

January 16

avg (50% prob, 32°F)

First fall frost

December 25

avg (50% prob, 32°F)

Growing season

349 days

frost-free window

Warmest month

September

avg high 80.1°F

Month-by-month typical weather in San Luis Obispo

Average conditions from the NOAA/NCEI 1991–2020 U.S. Climate Normals at San Luis Obispo Poly, CA (4.1 mi away). Temperatures °F, precipitation & snow in inches.

Month	Avg high	Avg low	Mean	Precip (in)
January	64.9	44	54.4	5.1
February	65.2	44.4	54.8	4.9
March	67.3	46.1	56.7	3.9
April	69.3	46.8	58	1.4
May	71.9	49.3	60.6	0.5
June	75.7	51.8	63.8	0.1
July	78.3	54.2	66.3	0.1
August	79.7	54.8	67.3	0
September	80.1	53.8	67	0.1
October	77.8	51.5	64.7	0.8
November	70.8	47.4	59.1	2
December	64.4	43.7	54	3.6

What to plant when in San Luis Obispo

Crop	Season	What to do & when
Tomatoes	warm	Start seeds indoors: December 5 · Transplant out: January 23
Peppers	warm	Start seeds indoors: November 21 · Transplant out: January 30
Cucumbers	warm	Direct sow: January 23
Zucchini / squash	warm	Direct sow: January 23
Bush beans	warm	Direct sow: January 23
Sweet corn	warm	Direct sow: January 23
Basil	warm	Transplant out: January 23
Peas	cool	Sow (spring): December 12 · Sow (fall): October 30
Spinach	cool	Sow (spring): December 5 · Sow (fall): October 30
Lettuce	cool	Sow (spring): December 19 · Sow (fall): October 30
Kale	cool	Transplant (spring): December 26 · Sow (fall): October 16
Broccoli	cool	Transplant (spring): January 2
Carrots	cool	Sow (spring): December 26 · Sow (fall): October 16
Onions	cool	Transplant (spring): December 19
Potatoes	cool	Plant seed potatoes: January 2
Radishes	cool	Sow (spring): December 19 · Sow (fall): November 13

Dates are computed from San Luis Obispo's average frost dates using standard cool-/warm-season timing. They're a starting point — a cold spring, a warm microclimate, or a fast-maturing variety can shift them by a week or two.

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Gear that helps you plant on time

Some links below are Amazon affiliate links (tag theboringthin-20). If you buy through them we may earn a small commission at no extra cost to you — it keeps this almanac free. We only list generic, genuinely-useful categories.

Soil thermometer →Know when the ground is warm enough to sow — the honest signal, not the calendar.Seed-starting trays + dome →Start tomatoes & peppers indoors on the schedule below.Seedling heat mat →Warms the soil for faster, more even germination indoors.Floating row cover / frost cloth →Buys you 4–8°F to beat an early or late frost.Raised garden bed kit →Warms and drains faster in spring than in-ground soil.Garden gloves →Basic kit for transplant day.

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Sources & method. Hardiness zone: 2023 USDA Plant Hardiness Zone Map (PRISM Climate Group, Oregon State University). Frost dates & growing season: NOAA/NCEI 1991–2020 U.S. Climate Normals, nearest station with published freeze normals — San Luis Obispo Poly, CA, 4.1 mi (confidence: high). Monthly weather normals: San Luis Obispo Poly, CA, 4.1 mi (confidence: high). ZIP centroid from U.S. Census 2023 ZCTA data. Frost dates are the 50%-probability date — half of years frost occurs outside the stated date. Nothing here is invented; where the nearest station is far, we say so. Last updated 2026-07-22.