When is the last frost in Riverside, CA?

The average last spring frost (50% probability of 32°F) in Riverside is around January 9, based on NOAA/NCEI 1991–2020 normals at the Riverside Fire Stn 3, CA station (3 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 Riverside?

The average first fall frost in Riverside, CA is around December 25, giving roughly a 353-day frost-free growing season.

What planting zone is Riverside, CA?

Riverside 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 Riverside?

In Riverside, CA the warmest month is August (avg high 96.8°F) and the coldest is December (avg low 42.1°F). It averages about 10″ of precipitation a year.

Home › California › Riverside

Riverside, CA Planting Calendar & Frost Dates

USDA hardiness zone 10a · ZIP 92504 · elevation 256′ · NOAA & USDA data

Riverside is in USDA hardiness zone 10a (winters can dip to 30 to 35°F), with a growing season of about 353 days between the average last spring frost (January 9) and first fall frost (December 25). The warmest month is August (avg high 96.8°F); the coldest is December (avg low 42.1°F). It averages 10″ 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 9

avg (50% prob, 32°F)

First fall frost

December 25

avg (50% prob, 32°F)

Growing season

353 days

frost-free window

Warmest month

August

avg high 96.8°F

Month-by-month typical weather in Riverside

Average conditions from the NOAA/NCEI 1991–2020 U.S. Climate Normals at Riverside Fire Stn 3, CA (3 mi away). Temperatures °F, precipitation & snow in inches.

Month	Avg high	Avg low	Mean	Precip (in)
January	69.8	43	56.4	2.2
February	69.7	44.1	56.9	2.5
March	73.1	46.2	59.6	1.6
April	78.2	49.7	63.9	0.6
May	81.4	54.7	68	0.2
June	88.9	59.2	74.1	0.1
July	95.3	63.7	79.5	0.1
August	96.8	64.5	80.7	0.1
September	93	61.8	77.4	0.2
October	84.3	54.5	69.4	0.4
November	76.3	46.5	61.4	0.7
December	69.1	42.1	55.6	1.4

What to plant when in Riverside

Crop	Season	What to do & when
Tomatoes	warm	Start seeds indoors: November 28 · Transplant out: January 16
Peppers	warm	Start seeds indoors: November 14 · Transplant out: January 23
Cucumbers	warm	Direct sow: January 16
Zucchini / squash	warm	Direct sow: January 16
Bush beans	warm	Direct sow: January 16
Sweet corn	warm	Direct sow: January 16
Basil	warm	Transplant out: January 16
Peas	cool	Sow (spring): December 5 · Sow (fall): October 30
Spinach	cool	Sow (spring): November 28 · Sow (fall): October 30
Lettuce	cool	Sow (spring): December 12 · Sow (fall): October 30
Kale	cool	Transplant (spring): December 19 · Sow (fall): October 16
Broccoli	cool	Transplant (spring): December 26
Carrots	cool	Sow (spring): December 19 · Sow (fall): October 16
Onions	cool	Transplant (spring): December 12
Potatoes	cool	Plant seed potatoes: December 26
Radishes	cool	Sow (spring): December 12 · Sow (fall): November 13

Dates are computed from Riverside'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 — Riverside Fire Stn 3, CA, 3 mi (confidence: high). Monthly weather normals: Riverside Fire Stn 3, CA, 3 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.