When is the last frost in Idaho Falls, ID?

The average last spring frost (50% probability of 32°F) in Idaho Falls is around May 9, based on NOAA/NCEI 1991–2020 normals at the Idaho Falls - Kifi, ID station (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 Idaho Falls?

The average first fall frost in Idaho Falls, ID is around October 1, giving roughly a 142-day frost-free growing season.

What planting zone is Idaho Falls, ID?

Idaho Falls 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 Idaho Falls?

In Idaho Falls, ID the warmest month is July (avg high 86.3°F) and the coldest is January (avg low 16.1°F). It averages about 13.5″ of precipitation a year.

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Idaho Falls, ID Planting Calendar & Frost Dates

USDA hardiness zone 5b · ZIP 83404 · elevation 1445′ · NOAA & USDA data

Idaho Falls is in USDA hardiness zone 5b (winters can dip to -15 to -10°F), with a growing season of about 142 days between the average last spring frost (May 9) and first fall frost (October 1). The warmest month is July (avg high 86.3°F); the coldest is January (avg low 16.1°F). It averages 13.5″ 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

min temp -15 to -10°F

Last spring frost

May 9

avg (50% prob, 32°F)

First fall frost

October 1

avg (50% prob, 32°F)

Growing season

142 days

frost-free window

Warmest month

July

avg high 86.3°F

Month-by-month typical weather in Idaho Falls

Average conditions from the NOAA/NCEI 1991–2020 U.S. Climate Normals at Idaho Falls - Kifi, ID (6 mi away). Temperatures °F, precipitation & snow in inches.

Month	Avg high	Avg low	Mean	Precip (in)	Snow (in)
January	30.2	16.1	23.2	1.1	–
February	35.7	20	27.9	1	–
March	48.2	28.5	38.4	1.3	–
April	57.8	34.3	46	1.4	–
May	67.2	42.4	54.8	1.9	–
June	76.6	48.7	62.6	1.3	–
July	86.3	55.2	70.8	0.5	–
August	85.5	53.6	69.5	0.7	–
September	74.9	45.3	60.1	1.1	–
October	59.4	34.8	47.1	1.2	–
November	43	25.1	34.1	1	–
December	30.8	17.2	24	1.1	–

What to plant when in Idaho Falls

Crop	Season	What to do & when
Tomatoes	warm	Start seeds indoors: March 28 · Transplant out: May 16
Peppers	warm	Start seeds indoors: March 14 · Transplant out: May 23
Cucumbers	warm	Direct sow: May 16
Zucchini / squash	warm	Direct sow: May 16
Bush beans	warm	Direct sow: May 16
Sweet corn	warm	Direct sow: May 16
Basil	warm	Transplant out: May 16
Peas	cool	Sow (spring): April 4 · Sow (fall): August 6
Spinach	cool	Sow (spring): March 28 · Sow (fall): August 6
Lettuce	cool	Sow (spring): April 11 · Sow (fall): August 6
Kale	cool	Transplant (spring): April 18 · Sow (fall): July 23
Broccoli	cool	Transplant (spring): April 25
Carrots	cool	Sow (spring): April 18 · Sow (fall): July 23
Onions	cool	Transplant (spring): April 11
Potatoes	cool	Plant seed potatoes: April 25
Radishes	cool	Sow (spring): April 11 · Sow (fall): August 20

Dates are computed from Idaho 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 Idaho

Pocatello, ID Twin Falls, ID Meridian, ID Nampa, ID Caldwell, ID

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 — Idaho Falls - Kifi, ID, 6 mi (confidence: high). Monthly weather normals: Idaho Falls - Kifi, ID, 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.