Frost Dates for Great Falls, MT 59404

Last spring frost May 24 · First fall frost September 14 · 113 frost-free days · USDA Zone 4b

Frost probability for 59404

Frost10%50%90%
Spring (last frost)June 8May 24May 8
Fall (first frost)September 4September 14September 26

Dates come from NOAA 1971–2000 freeze probabilities at the nearest reporting station (53.4 km away); the 50% date is the median year.

Month by month in Great 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).
MarchStart peppers and eggplant indoors 8–10 weeks before your last frost (around May 24). Start tomatoes about two weeks later, 6–8 weeks before last frost.
AprilStart herbs, basil, and squash indoors (4–6 weeks before frost). Direct sow peas, spinach, and lettuce if soil is workable.
MayLast frost around May 24. Transplant cold-hardy crops (broccoli, kale, cabbage). Harden off tomato and pepper seedlings.
JuneFrost has passed. Transplant tomatoes, peppers, and basil outdoors. Direct sow beans, cucumbers, squash, and zucchini.
JulySuccession plant lettuce and greens. Keep beds weeded and watered consistently.
AugustFirst fall frost approaching (around September 14). Transplant fall brassicas. Sow spinach, arugula, and radishes.
SeptemberFirst frost around September 14. 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 113-day season

Frequently Asked Questions

What is the last frost date for Great Falls, MT (ZIP 59404)?

The median last spring frost date for Great Falls, MT (ZIP code 59404) is around May 24. 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 Great Falls, MT?

The median first fall frost date for Great Falls, MT is around September 14. 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 Great Falls, MT?

The frost-free growing season in Great Falls is about 113 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 Great Falls, MT?

Based on frost date patterns, Great Falls falls approximately in 4b. 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 Great Falls, MT?

Start tomato seeds indoors 6–8 weeks before your last frost date (around May 24). For Great Falls, that's roughly March 29 to April 12. Transplant outdoors 1–2 weeks after your last frost.

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