When is the last frost in Palo Alto, CA?

The average last spring frost (50% probability of 32°F) in Palo Alto is around February 1, based on NOAA/NCEI 1991–2020 normals at the Palo Alto, CA station (2 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 Palo Alto?

The average first fall frost in Palo Alto, CA is around December 7, giving roughly a 310-day frost-free growing season.

What planting zone is Palo Alto, CA?

Palo Alto 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 Palo Alto?

In Palo Alto, CA the warmest month is September (avg high 79.6°F) and the coldest is December (avg low 38.6°F). It averages about 15.1″ of precipitation a year.

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Palo Alto, CA Planting Calendar & Frost Dates

USDA hardiness zone 9b · ZIP 94306 · elevation 8′ · NOAA & USDA data

Palo Alto is in USDA hardiness zone 9b (winters can dip to 25 to 30°F), with a growing season of about 310 days between the average last spring frost (February 1) and first fall frost (December 7). The warmest month is September (avg high 79.6°F); the coldest is December (avg low 38.6°F). It averages 15.1″ 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

February 1

avg (50% prob, 32°F)

First fall frost

December 7

avg (50% prob, 32°F)

Growing season

310 days

frost-free window

Warmest month

September

avg high 79.6°F

Month-by-month typical weather in Palo Alto

Average conditions from the NOAA/NCEI 1991–2020 U.S. Climate Normals at Palo Alto, CA (2 mi away). Temperatures °F, precipitation & snow in inches.

Month	Avg high	Avg low	Mean	Precip (in)
January	57.8	39	48.4	3
February	60.7	41.3	51	3.2
March	65.5	43.6	54.6	2.2
April	69.6	45.3	57.4	1
May	73.3	49.5	61.4	0.4
June	78.5	52.7	65.6	0.1
July	79.4	55.7	67.6	0
August	78.7	55.3	67	0
September	79.6	53	66.3	0.1
October	74	48.4	61.2	0.6
November	63.7	42.5	53.1	1.6
December	57.6	38.6	48.1	3

What to plant when in Palo Alto

Crop	Season	What to do & when
Tomatoes	warm	Start seeds indoors: December 21 · Transplant out: February 8
Peppers	warm	Start seeds indoors: December 7 · Transplant out: February 15
Cucumbers	warm	Direct sow: February 8
Zucchini / squash	warm	Direct sow: February 8
Bush beans	warm	Direct sow: February 8
Sweet corn	warm	Direct sow: February 8
Basil	warm	Transplant out: February 8
Peas	cool	Sow (spring): December 28 · Sow (fall): October 12
Spinach	cool	Sow (spring): December 21 · Sow (fall): October 12
Lettuce	cool	Sow (spring): January 4 · Sow (fall): October 12
Kale	cool	Transplant (spring): January 11 · Sow (fall): September 28
Broccoli	cool	Transplant (spring): January 18
Carrots	cool	Sow (spring): January 11 · Sow (fall): September 28
Onions	cool	Transplant (spring): January 4
Potatoes	cool	Plant seed potatoes: January 18
Radishes	cool	Sow (spring): January 4 · Sow (fall): October 26

Dates are computed from Palo Alto'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 — Palo Alto, CA, 2 mi (confidence: high). Monthly weather normals: Palo Alto, CA, 2 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.