St. Mary 1 SSW, MT Frost Dates & Growing Season

The two dates every St. Mary 1 SSW garden is planned around, plus ready-computed planting windows for the most popular crops.

Last spring frost
Jun 3
~50% chance of frost after
First fall frost
Sep 8
~50% chance of frost before
Growing season
97 days
frost-free stretch
USDA zone
≈ 4b
estimated from nearby reference
Risky (1 year in 10)MedianSafe (9 years in 10)
Last spring frost May 19 Jun 3 Jun 23
First fall frost Sep 26 Sep 8 Aug 22
Hard freeze (28°F), median last May 14 · first Sep 25

Computed from NOAA 1991–2020 climate normals at the ST. MARY 1 SSW station. "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 St. Mary 1 SSW

Computed from St. Mary 1 SSW'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 Apr 8 – Apr 22 Jun 10 – Jun 17
🫑 Peppers Mar 25 – Apr 8 Jun 17 – Jun 24
🥬 Lettuce Apr 22 – May 6 May 6 – May 20 May 6 – Jun 3
🫛 Peas Apr 22 – May 6
🥕 Carrots May 13 – Jun 3
🥦 Broccoli Apr 15 – Apr 29 May 13 – May 27
🥬 Kale Apr 22 – May 6 May 6 – May 20 May 6 – May 20
🥒 Cucumbers May 6 – May 13 Jun 10 – Jun 17 Jun 10 – Jun 17
🥒 Zucchini May 6 – May 13 Jun 10 – Jun 17 Jun 10 – Jun 17
🫘 Green Beans (Bush) Jun 10 – Jun 17
🌽 Sweet Corn Jun 10 – Jun 17
🌿 Basil Apr 22 – May 6 Jun 10 – Jun 17 Jun 17 – Jun 24
🧄 Garlic Fall: Jul 28 – Aug 25

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 St. Mary 1 SSW's dates automatically after a lookup.

Reading the season in St. Mary 1 SSW

At about 97 frost-free days, St. Mary 1 SSW 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 St. Mary 1 SSW, MT?

The average last spring frost in St. Mary 1 SSW is around Jun 3, 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 St. Mary 1 SSW, MT?

The average first fall frost in St. Mary 1 SSW arrives around Sep 8. 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 St. Mary 1 SSW?

About 97 frost-free days on average, from Jun 3 to Sep 8. 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 St. Mary 1 SSW 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.