Frost Dates for Missoula, MT 59801

Last spring frost May 26 · First fall frost September 18 · 115 frost-free days · USDA Zone 5b

Frost probability for 59801

Frost10%50%90%
Spring (last frost)June 15May 26May 6
Fall (first frost)September 4September 18October 2

Dates come from NOAA 1971–2000 freeze probabilities at the nearest reporting station (9.7 km away); the 50% date is the median year.

Frost dates by ZIP code in Missoula, MT

ZIPLast spring frost (50%)First fall frost (50%)Zone
59801May 26September 185b
59808May 23September 195b
59802May 26September 185b
59803May 26September 185b
59804May 26September 185b
59812May 26September 185b

Month by month in Missoula

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 26). 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 26. 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 18). Transplant fall brassicas. Sow spinach, arugula, and radishes.
SeptemberFirst frost around September 18. 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 115-day season

Frequently Asked Questions

What is the last frost date for Missoula, MT (ZIP 59801)?

The median last spring frost date for Missoula, MT (ZIP code 59801) is around May 26. 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 Missoula, MT?

The median first fall frost date for Missoula, MT is around September 18. 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 Missoula, MT?

The frost-free growing season in Missoula is about 115 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 Missoula, MT?

Based on frost date patterns, Missoula 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 Missoula, MT?

Start tomato seeds indoors 6–8 weeks before your last frost date (around May 26). For Missoula, that's roughly March 31 to April 14. Transplant outdoors 1–2 weeks after your last frost.

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