When is the last frost in Monrovia, CA?

The average last spring frost (50% probability of 32°F) in Monrovia is around April 28, based on NOAA/NCEI 1991–2020 normals at the Mt Wilson Cbs, CA station (6.7 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 Monrovia?

The average first fall frost in Monrovia, CA is around November 15, giving roughly a 199-day frost-free growing season.

What planting zone is Monrovia, CA?

Monrovia 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 Monrovia?

In Monrovia, CA the warmest month is August (avg high 87.6°F) and the coldest is December (avg low 45.3°F). It averages about 15.7″ of precipitation a year.

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Monrovia, CA Planting Calendar & Frost Dates

USDA hardiness zone 10a · ZIP 91016 · elevation 111′ · NOAA & USDA data

Monrovia is in USDA hardiness zone 10a (winters can dip to 30 to 35°F), with a growing season of about 199 days between the average last spring frost (April 28) and first fall frost (November 15). The warmest month is August (avg high 87.6°F); the coldest is December (avg low 45.3°F). It averages 15.7″ 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

April 28

avg (50% prob, 32°F)

First fall frost

November 15

avg (50% prob, 32°F)

Growing season

199 days

frost-free window

Warmest month

August

avg high 87.6°F

Month-by-month typical weather in Monrovia

Average conditions from the NOAA/NCEI 1991–2020 U.S. Climate Normals at San Gabriel Fire Dept, CA (7.4 mi away). Temperatures °F, precipitation & snow in inches.

Month	Avg high	Avg low	Mean	Precip (in)
January	68.6	46.1	57.4	3.6
February	68.2	47.1	57.7	4.2
March	70.9	50.5	60.7	2.5
April	73.8	52.7	63.2	0.6
May	75.6	57.6	66.6	0.5
June	80.8	61.5	71.2	0.1
July	85.5	65.2	75.4	0
August	87.6	65.5	76.6	0
September	86.7	63.6	75.1	0.1
October	80.7	57.4	69	0.6
November	74	50.6	62.3	0.9
December	67.8	45.3	56.6	2.4

What to plant when in Monrovia

Crop	Season	What to do & when
Tomatoes	warm	Start seeds indoors: March 17 · Transplant out: May 5
Peppers	warm	Start seeds indoors: March 3 · Transplant out: May 12
Cucumbers	warm	Direct sow: May 5
Zucchini / squash	warm	Direct sow: May 5
Bush beans	warm	Direct sow: May 5
Sweet corn	warm	Direct sow: May 5
Basil	warm	Transplant out: May 5
Peas	cool	Sow (spring): March 24 · Sow (fall): September 20
Spinach	cool	Sow (spring): March 17 · Sow (fall): September 20
Lettuce	cool	Sow (spring): March 31 · Sow (fall): September 20
Kale	cool	Transplant (spring): April 7 · Sow (fall): September 6
Broccoli	cool	Transplant (spring): April 14
Carrots	cool	Sow (spring): April 7 · Sow (fall): September 6
Onions	cool	Transplant (spring): March 31
Potatoes	cool	Plant seed potatoes: April 14
Radishes	cool	Sow (spring): March 31 · Sow (fall): October 4

Dates are computed from Monrovia'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 Wilson Cbs, CA, 6.7 mi (confidence: high). Monthly weather normals: San Gabriel Fire Dept, CA, 7.4 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.