When is the last frost in Walnut Creek, CA?

The average last spring frost (50% probability of 32°F) in Walnut Creek is around March 8, based on NOAA/NCEI 1991–2020 normals at the Mt Diablo Junction, CA station (5.8 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 Walnut Creek?

The average first fall frost in Walnut Creek, CA is around December 22, giving roughly a 282-day frost-free growing season.

What planting zone is Walnut Creek, CA?

Walnut Creek 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 Walnut Creek?

In Walnut Creek, CA the warmest month is August (avg high 82.8°F) and the coldest is December (avg low 41.3°F). It averages about 26.1″ of precipitation a year and 0.7″ of snow.

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Walnut Creek, CA Planting Calendar & Frost Dates

USDA hardiness zone 9b · ZIP 94596 · elevation 661′ · NOAA & USDA data

Walnut Creek is in USDA hardiness zone 9b (winters can dip to 25 to 30°F), with a growing season of about 282 days between the average last spring frost (March 8) and first fall frost (December 22). The warmest month is August (avg high 82.8°F); the coldest is December (avg low 41.3°F). It averages 26.1″ of precipitation a year and 0.7″ of snow, mostly mid-winter. 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

March 8

avg (50% prob, 32°F)

First fall frost

December 22

avg (50% prob, 32°F)

Growing season

282 days

frost-free window

Warmest month

August

avg high 82.8°F

Month-by-month typical weather in Walnut Creek

Average conditions from the NOAA/NCEI 1991–2020 U.S. Climate Normals at Mt Diablo Junction, CA (5.8 mi away). Temperatures °F, precipitation & snow in inches.

Month	Avg high	Avg low	Mean	Precip (in)	Snow (in)
January	53.7	41.7	47.7	5.1	0.1
February	54.6	41.7	48.2	4.9	0.5
March	57.9	42.9	50.4	3.7	0.1
April	62	44.4	53.2	1.9	0
May	67.8	49.3	58.6	1.1	0
June	75.9	55.4	65.6	0.3	0
July	82.5	61.5	72	0	0
August	82.8	61	71.9	0	0
September	80	59.7	69.9	0.1	0
October	71.7	54	62.9	1.2	0
November	60.4	46.2	53.3	2.7	0
December	53.4	41.3	47.4	5.1	0

What to plant when in Walnut Creek

Crop	Season	What to do & when
Tomatoes	warm	Start seeds indoors: January 25 · Transplant out: March 15
Peppers	warm	Start seeds indoors: January 11 · Transplant out: March 22
Cucumbers	warm	Direct sow: March 15
Zucchini / squash	warm	Direct sow: March 15
Bush beans	warm	Direct sow: March 15
Sweet corn	warm	Direct sow: March 15
Basil	warm	Transplant out: March 15
Peas	cool	Sow (spring): February 1 · Sow (fall): October 27
Spinach	cool	Sow (spring): January 25 · Sow (fall): October 27
Lettuce	cool	Sow (spring): February 8 · Sow (fall): October 27
Kale	cool	Transplant (spring): February 15 · Sow (fall): October 13
Broccoli	cool	Transplant (spring): February 22
Carrots	cool	Sow (spring): February 15 · Sow (fall): October 13
Onions	cool	Transplant (spring): February 8
Potatoes	cool	Plant seed potatoes: February 22
Radishes	cool	Sow (spring): February 8 · Sow (fall): November 10

Dates are computed from Walnut Creek'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

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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 — Mt Diablo Junction, CA, 5.8 mi (confidence: high). Monthly weather normals: Mt Diablo Junction, CA, 5.8 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.