When is the last frost in Great Falls, MT?

The average last spring frost (50% probability of 32°F) in Great Falls is around May 6, based on NOAA/NCEI 1991–2020 normals at the Great Falls 16st, MT station (1.6 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 Great Falls?

The average first fall frost in Great Falls, MT is around October 1, giving roughly a 147-day frost-free growing season.

What planting zone is Great Falls, MT?

Great Falls is in USDA plant hardiness zone 4b (average annual extreme minimum temperature -25 to -20°F), from the 2023 USDA Plant Hardiness Zone Map.

What is the weather like in Great Falls?

In Great Falls, MT the warmest month is July (avg high 84.3°F) and the coldest is January (avg low 15°F). It averages about 14.8″ of precipitation a year and 66.1″ of snow.

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Great Falls, MT Planting Calendar & Frost Dates

USDA hardiness zone 4b · ZIP 59401 · elevation 1117′ · NOAA & USDA data

Great Falls is in USDA hardiness zone 4b (winters can dip to -25 to -20°F), with a growing season of about 147 days between the average last spring frost (May 6) and first fall frost (October 1). The warmest month is July (avg high 84.3°F); the coldest is January (avg low 15°F). It averages 14.8″ of precipitation a year and 66.1″ 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 -20°F

Last spring frost

May 6

avg (50% prob, 32°F)

First fall frost

October 1

avg (50% prob, 32°F)

Growing season

147 days

frost-free window

Warmest month

July

avg high 84.3°F

Month-by-month typical weather in Great Falls

Average conditions from the NOAA/NCEI 1991–2020 U.S. Climate Normals at Great Falls Intl Ap, MT (5.6 mi away). Temperatures °F, precipitation & snow in inches.

Month	Avg high	Avg low	Mean	Precip (in)	Snow (in)
January	35.3	15	25.2	0.6	9.2
February	37.1	15.4	26.2	0.6	10.1
March	46.1	22.1	34.1	0.7	10.1
April	54.9	29.9	42.4	1.7	9.4
May	64.6	38.4	51.5	2.4	1.9
June	72.8	45.9	59.4	2.7	0.3
July	84.3	51.4	67.9	1.2	0
August	83.2	50.3	66.7	1.2	0.3
September	71.7	42.8	57.2	1.3	0.8
October	57	32.6	44.8	1.1	5.2
November	43.7	23.6	33.6	0.7	9.2
December	35.6	16.3	26	0.5	9.6

What to plant when in Great Falls

Crop	Season	What to do & when
Tomatoes	warm	Start seeds indoors: March 25 · Transplant out: May 13
Peppers	warm	Start seeds indoors: March 11 · Transplant out: May 20
Cucumbers	warm	Direct sow: May 13
Zucchini / squash	warm	Direct sow: May 13
Bush beans	warm	Direct sow: May 13
Sweet corn	warm	Direct sow: May 13
Basil	warm	Transplant out: May 13
Peas	cool	Sow (spring): April 1 · Sow (fall): August 6
Spinach	cool	Sow (spring): March 25 · Sow (fall): August 6
Lettuce	cool	Sow (spring): April 8 · Sow (fall): August 6
Kale	cool	Transplant (spring): April 15 · Sow (fall): July 23
Broccoli	cool	Transplant (spring): April 22
Carrots	cool	Sow (spring): April 15 · Sow (fall): July 23
Onions	cool	Transplant (spring): April 8
Potatoes	cool	Plant seed potatoes: April 22
Radishes	cool	Sow (spring): April 8 · Sow (fall): August 20

Dates are computed from Great Falls'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 Montana

Bozeman, MT Missoula, MT Billings, MT

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 — Great Falls 16st, MT, 1.6 mi (confidence: high). Monthly weather normals: Great Falls Intl Ap, MT, 5.6 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.