When is the last frost in San Mateo, CA?

The average last spring frost (50% probability of 32°F) in San Mateo is around January 17, based on NOAA/NCEI 1991–2020 normals at the Redwood City, CA station (5.6 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 Mateo?

The average first fall frost in San Mateo, CA is around December 12, giving roughly a 333-day frost-free growing season.

What planting zone is San Mateo, CA?

San Mateo is in USDA plant hardiness zone 10a (average annual extreme minimum temperature 30 to 35°F), from the 2023 USDA Plant Hardiness Zone Map.

What is the weather like in San Mateo?

In San Mateo, CA the warmest month is July (avg high 81°F) and the coldest is December (avg low 40.2°F). It averages about 19″ of precipitation a year.

Home › California › San Mateo

San Mateo, CA Planting Calendar & Frost Dates

USDA hardiness zone 10a · ZIP 94403 · elevation 9′ · NOAA & USDA data

San Mateo is in USDA hardiness zone 10a (winters can dip to 30 to 35°F), with a growing season of about 333 days between the average last spring frost (January 17) and first fall frost (December 12). The warmest month is July (avg high 81°F); the coldest is December (avg low 40.2°F). It averages 19″ 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

10a

min temp 30 to 35°F

Last spring frost

January 17

avg (50% prob, 32°F)

First fall frost

December 12

avg (50% prob, 32°F)

Growing season

333 days

frost-free window

Warmest month

July

avg high 81°F

Month-by-month typical weather in San Mateo

Average conditions from the NOAA/NCEI 1991–2020 U.S. Climate Normals at Redwood City, CA (5.6 mi away). Temperatures °F, precipitation & snow in inches.

Month	Avg high	Avg low	Mean	Precip (in)
January	58.9	40.5	49.7	3.8
February	61.9	42.5	52.2	3.7
March	65.3	44.6	54.9	3
April	68.5	46.5	57.5	1.2
May	72.9	50.4	61.6	0.5
June	78.8	53.6	66.2	0.2
July	81	56.6	68.8	0
August	80.8	56.5	68.7	0
September	79.3	54.3	66.8	0.1
October	74.6	49.8	62.2	0.9
November	64.7	43.9	54.3	1.9
December	58.6	40.2	49.4	3.9

What to plant when in San Mateo

Crop	Season	What to do & when
Tomatoes	warm	Start seeds indoors: December 6 · Transplant out: January 24
Peppers	warm	Start seeds indoors: November 22 · Transplant out: January 31
Cucumbers	warm	Direct sow: January 24
Zucchini / squash	warm	Direct sow: January 24
Bush beans	warm	Direct sow: January 24
Sweet corn	warm	Direct sow: January 24
Basil	warm	Transplant out: January 24
Peas	cool	Sow (spring): December 13 · Sow (fall): October 17
Spinach	cool	Sow (spring): December 6 · Sow (fall): October 17
Lettuce	cool	Sow (spring): December 20 · Sow (fall): October 17
Kale	cool	Transplant (spring): December 27 · Sow (fall): October 3
Broccoli	cool	Transplant (spring): January 3
Carrots	cool	Sow (spring): December 27 · Sow (fall): October 3
Onions	cool	Transplant (spring): December 20
Potatoes	cool	Plant seed potatoes: January 3
Radishes	cool	Sow (spring): December 20 · Sow (fall): October 31

Dates are computed from San Mateo'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.

Nearby cities in California

Redwood City, CA San Bruno, CA South San Francisco, CA Pacifica, CA Palo Alto, CA San Leandro, CA Union City, CA Daly City, CA

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 — Redwood City, CA, 5.6 mi (confidence: high). Monthly weather normals: Redwood City, CA, 5.6 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.