When is the last frost in Fort Collins, CO?

The average last spring frost (50% probability of 32°F) in Fort Collins is around May 2, based on NOAA/NCEI 1991–2020 normals at the Ft Collins, CO station (2.5 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 Fort Collins?

The average first fall frost in Fort Collins, CO is around October 7, giving roughly a 157-day frost-free growing season.

What planting zone is Fort Collins, CO?

Fort Collins is in USDA plant hardiness zone 5b (average annual extreme minimum temperature -15 to -10°F), from the 2023 USDA Plant Hardiness Zone Map.

What is the weather like in Fort Collins?

In Fort Collins, CO the warmest month is July (avg high 87.4°F) and the coldest is January (avg low 18.3°F). It averages about 15.9″ of precipitation a year and 51.4″ of snow.

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Fort Collins, CO Planting Calendar & Frost Dates

USDA hardiness zone 5b · ZIP 80521 · elevation 1525′ · NOAA & USDA data

Fort Collins is in USDA hardiness zone 5b (winters can dip to -15 to -10°F), with a growing season of about 157 days between the average last spring frost (May 2) and first fall frost (October 7). The warmest month is July (avg high 87.4°F); the coldest is January (avg low 18.3°F). It averages 15.9″ of precipitation a year and 51.4″ 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 -15 to -10°F

Last spring frost

May 2

avg (50% prob, 32°F)

First fall frost

October 7

avg (50% prob, 32°F)

Growing season

157 days

frost-free window

Warmest month

July

avg high 87.4°F

Month-by-month typical weather in Fort Collins

Average conditions from the NOAA/NCEI 1991–2020 U.S. Climate Normals at Ft Collins, CO (2.5 mi away). Temperatures °F, precipitation & snow in inches.

Month	Avg high	Avg low	Mean	Precip (in)	Snow (in)
January	45	18.3	31.6	0.4	6.7
February	46.8	20.7	33.8	0.5	7.6
March	56.4	28.5	42.4	1.3	9.4
April	62.5	35.4	49	2.1	6.2
May	70.9	44.1	57.5	2.7	1.6
June	81.8	52.8	67.3	1.9	0
July	87.4	58.7	73.1	1.6	0
August	85	56.5	70.7	1.5	0
September	77.4	48	62.7	1.4	0.7
October	64.3	36.1	50.2	1.3	4.1
November	52.5	26.1	39.3	0.7	7.6
December	44	18.3	31.1	0.5	7.5

What to plant when in Fort Collins

Crop	Season	What to do & when
Tomatoes	warm	Start seeds indoors: March 21 · Transplant out: May 9
Peppers	warm	Start seeds indoors: March 7 · Transplant out: May 16
Cucumbers	warm	Direct sow: May 9
Zucchini / squash	warm	Direct sow: May 9
Bush beans	warm	Direct sow: May 9
Sweet corn	warm	Direct sow: May 9
Basil	warm	Transplant out: May 9
Peas	cool	Sow (spring): March 28 · Sow (fall): August 12
Spinach	cool	Sow (spring): March 21 · Sow (fall): August 12
Lettuce	cool	Sow (spring): April 4 · Sow (fall): August 12
Kale	cool	Transplant (spring): April 11 · Sow (fall): July 29
Broccoli	cool	Transplant (spring): April 18
Carrots	cool	Sow (spring): April 11 · Sow (fall): July 29
Onions	cool	Transplant (spring): April 4
Potatoes	cool	Plant seed potatoes: April 18
Radishes	cool	Sow (spring): April 4 · Sow (fall): August 26

Dates are computed from Fort Collins'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 Colorado

Loveland, CO Greeley, CO Longmont, CO Boulder, CO Broomfield, CO Thornton, CO Westminster, CO Commerce City, CO

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 — Ft Collins, CO, 2.5 mi (confidence: high). Monthly weather normals: Ft Collins, CO, 2.5 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.