Great Falls, MT Frost Dates & Growing Season

The two dates every Great Falls garden is planned around, plus ready-computed planting windows for the most popular crops.

Last spring frost
May 6
~50% chance of frost after
First fall frost
Oct 1
~50% chance of frost before
Growing season
148 days
frost-free stretch
USDA zone
4b
2023 hardiness map
Risky (1 year in 10)MedianSafe (9 years in 10)
Last spring frost Apr 23 May 6 May 19
First fall frost Oct 16 Oct 1 Sep 17
Hard freeze (28°F), median last Apr 24 · first Oct 11

Computed from NOAA 1991–2020 climate normals at the Great Falls 16ST station (3 km from central Great Falls). "Safe" means frost past that date happens only about one year in ten. Your exact garden can still run days either way with elevation and terrain — check your own ZIP with the frost date lookup.

Planting windows for Great Falls

Computed from Great Falls's own frost dates. Click any crop for the full zone-4 growing guide — varieties, spacing, fall plantings, and more.

CropStart seeds indoorsTransplantDirect sow
🍅 Tomatoes Mar 11 – Mar 25 May 13 – May 20
🫑 Peppers Feb 25 – Mar 11 May 20 – May 27
🥬 Lettuce Mar 25 – Apr 8 Apr 8 – Apr 22 Apr 8 – May 6
🫛 Peas Mar 25 – Apr 8
🥕 Carrots Apr 15 – May 6
🥦 Broccoli Mar 18 – Apr 1 Apr 15 – Apr 29
🥬 Kale Mar 25 – Apr 8 Apr 8 – Apr 22 Apr 8 – Apr 22
🥒 Cucumbers Apr 8 – Apr 15 May 13 – May 20 May 13 – May 20
🥒 Zucchini Apr 8 – Apr 15 May 13 – May 20 May 13 – May 20
🫘 Green Beans (Bush) May 13 – May 20
🌽 Sweet Corn May 13 – May 20
🌿 Basil Mar 25 – Apr 8 May 13 – May 20 May 20 – May 27
🧄 Garlic Fall: Aug 20 – Sep 17

Want this for all 50 crops, or as a printable seed-shelf schedule? Use the planting calendar and the seed starting scheduler — both can use Great Falls's dates automatically after a lookup.

Reading the season in Great Falls

At about 148 frost-free days, Great Falls rewards efficiency: start warm-season crops indoors, favor short-season varieties, and lean on cold-tolerant crops — peas, kale, roots — that shrug off the shoulder-season frosts on either end.

Frequently asked questions

When is the last frost in Great Falls, MT?

The average last spring frost in Great Falls is around May 6, based on 1991–2020 climate normals. That's a median — about half of years see a later frost, so tender crops are safest going out a week or two after this date.

When is the first frost in Great Falls, MT?

The average first fall frost in Great Falls arrives around Oct 1. Crops still in the garden need to mature before then, and frost-tender plants need harvesting or protection as the date approaches.

How long is the growing season in Great Falls?

About 148 frost-free days on average, from May 6 to Oct 1. That favors short-season varieties and transplants for warm-season crops, with cool-season vegetables doing the heavy lifting in spring and fall.

What USDA zone is Great Falls in?

USDA zone 4b on the 2023 Plant Hardiness Zone Map. Note that zones describe winter cold, not frost timing — these frost dates are the numbers to plan plantings around.