Shonkin 7 S, MT Frost Dates & Growing Season

The two dates every Shonkin 7 S garden is planned around, plus ready-computed planting windows for the most popular crops.

Last spring frost
May 24
~50% chance of frost after
First fall frost
Sep 21
~50% chance of frost before
Growing season
120 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 6 May 24 Jun 10
First fall frost Oct 5 Sep 21 Aug 31
Hard freeze (28°F), median last May 7 · first Oct 1

Computed from NOAA 1991–2020 climate normals at the SHONKIN 7 S 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 Shonkin 7 S

Computed from Shonkin 7 S'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 29 – Apr 12 May 31 – Jun 7
🫑 Peppers Mar 15 – Mar 29 Jun 7 – Jun 14
🥬 Lettuce Apr 12 – Apr 26 Apr 26 – May 10 Apr 26 – May 24
🫛 Peas Apr 12 – Apr 26
🥕 Carrots May 3 – May 24
🥦 Broccoli Apr 5 – Apr 19 May 3 – May 17
🥬 Kale Apr 12 – Apr 26 Apr 26 – May 10 Apr 26 – May 10
🥒 Cucumbers Apr 26 – May 3 May 31 – Jun 7 May 31 – Jun 7
🥒 Zucchini Apr 26 – May 3 May 31 – Jun 7 May 31 – Jun 7
🫘 Green Beans (Bush) May 31 – Jun 7
🌽 Sweet Corn May 31 – Jun 7
🌿 Basil Apr 12 – Apr 26 May 31 – Jun 7 Jun 7 – Jun 14
🧄 Garlic Fall: Aug 10 – Sep 7

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 Shonkin 7 S's dates automatically after a lookup.

Reading the season in Shonkin 7 S

At about 120 frost-free days, Shonkin 7 S 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 Shonkin 7 S, MT?

The average last spring frost in Shonkin 7 S is around May 24, 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 Shonkin 7 S, MT?

The average first fall frost in Shonkin 7 S arrives around Sep 21. 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 Shonkin 7 S?

About 120 frost-free days on average, from May 24 to Sep 21. 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 Shonkin 7 S 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.