Frost Dates for Idaho Falls, ID 83401

Last spring frost June 12 · First fall frost September 5 · 85 frost-free days · USDA Zone 5b

Frost probability for 83401

Frost10%50%90%
Spring (last frost)July 6June 12May 19
Fall (first frost)August 16September 5September 25

Dates come from NOAA 1971–2000 freeze probabilities at the nearest reporting station (49.0 km away); the 50% date is the median year.

Frost dates by ZIP code in Idaho Falls, ID

ZIPLast spring frost (50%)First fall frost (50%)Zone
83401June 12September 55b
83402May 28September 185b
83404May 28September 185b
83406May 28September 185b

Month by month in Idaho Falls

MonthWhat to do
JanuaryPlan your garden layout and order seeds. Research varieties suited to your frost dates.
FebruaryStart the slowest-growing crops indoors: onions, leeks, and celery (10–12 weeks before last frost).
MarchOrganize planting supplies and seed-starting mix. Check stored garden tools.
AprilStart peppers and eggplant indoors 8–10 weeks before your last frost (around June 12). Start tomatoes about two weeks later, 6–8 weeks before last frost.
MayStart herbs, basil, and squash indoors (4–6 weeks before frost). Direct sow peas, spinach, and lettuce if soil is workable.
JuneLast frost around June 12. Transplant cold-hardy crops (broccoli, kale, cabbage). Harden off tomato and pepper seedlings.
JulyFrost has passed. Transplant tomatoes, peppers, and basil outdoors. Direct sow beans, cucumbers, squash, and zucchini.
AugustFirst fall frost approaching (around September 5). Transplant fall brassicas. Sow spinach, arugula, and radishes.
SeptemberFirst frost around September 5. Harvest tomatoes and peppers before frost. Cover cold-hardy crops with row covers to extend the season.
OctoberHarvest remaining cold-hardy crops: kale, carrots, and beets. Plant garlic bulbs for next year.
NovemberClean up spent plants. Add compost to beds. Rest, review, and plan next year's garden.
DecemberClean up spent plants. Add compost to beds. Rest, review, and plan next year's garden.

What grows in a 85-day season

Frequently Asked Questions

What is the last frost date for Idaho Falls, ID (ZIP 83401)?

The median last spring frost date for Idaho Falls, ID (ZIP code 83401) is around June 12. This is the 50th-percentile date — meaning half of all years see frost end before this date. Use the 10% and 90% dates to understand the full range of risk in your area.

What is the first fall frost date in Idaho Falls, ID?

The median first fall frost date for Idaho Falls, ID is around September 5. Plan to harvest or protect frost-sensitive crops like tomatoes and peppers at least a week before this date to avoid losses.

How long is the growing season in Idaho Falls, ID?

The frost-free growing season in Idaho Falls is about 85 days. This window — from your last spring frost to your first fall frost — is when warm-season vegetables thrive. Cold-hardy crops like kale, spinach, and peas can extend your season by weeks on either side.

What USDA hardiness zone is Idaho Falls, ID?

Based on frost date patterns, Idaho Falls falls approximately in 5b. USDA hardiness zones are determined by average annual minimum winter temperatures and guide both plant selection and planting timing for your location.

When should I start tomatoes indoors in Idaho Falls, ID?

Start tomato seeds indoors 6–8 weeks before your last frost date (around June 12). For Idaho Falls, that's roughly April 17 to May 1. Transplant outdoors 1–2 weeks after your last frost.

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