Bynum 4 SSE, MT Frost Dates & Growing Season

The two dates every Bynum 4 SSE garden is planned around, plus ready-computed planting windows for the most popular crops.

Last spring frost
May 16
~50% chance of frost after
First fall frost
Sep 27
~50% chance of frost before
Growing season
134 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 2 May 16 May 28
First fall frost Oct 9 Sep 27 Sep 16
Hard freeze (28°F), median last May 2 · first Oct 6

Computed from NOAA 1991–2020 climate normals at the BYNUM 4 SSE 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 Bynum 4 SSE

Computed from Bynum 4 SSE'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 21 – Apr 4 May 23 – May 30
🫑 Peppers Mar 7 – Mar 21 May 30 – Jun 6
🥬 Lettuce Apr 4 – Apr 18 Apr 18 – May 2 Apr 18 – May 16
🫛 Peas Apr 4 – Apr 18
🥕 Carrots Apr 25 – May 16
🥦 Broccoli Mar 28 – Apr 11 Apr 25 – May 9
🥬 Kale Apr 4 – Apr 18 Apr 18 – May 2 Apr 18 – May 2
🥒 Cucumbers Apr 18 – Apr 25 May 23 – May 30 May 23 – May 30
🥒 Zucchini Apr 18 – Apr 25 May 23 – May 30 May 23 – May 30
🫘 Green Beans (Bush) May 23 – May 30
🌽 Sweet Corn May 23 – May 30
🌿 Basil Apr 4 – Apr 18 May 23 – May 30 May 30 – Jun 6
🧄 Garlic Fall: Aug 16 – Sep 13

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 Bynum 4 SSE's dates automatically after a lookup.

Reading the season in Bynum 4 SSE

At about 134 frost-free days, Bynum 4 SSE 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 Bynum 4 SSE, MT?

The average last spring frost in Bynum 4 SSE is around May 16, 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 Bynum 4 SSE, MT?

The average first fall frost in Bynum 4 SSE arrives around Sep 27. 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 Bynum 4 SSE?

About 134 frost-free days on average, from May 16 to Sep 27. 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 Bynum 4 SSE 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.