Biddle 8 SW, MT Frost Dates & Growing Season

The two dates every Biddle 8 SW garden is planned around, plus ready-computed planting windows for the most popular crops.

Last spring frost
May 14
~50% chance of frost after
First fall frost
Sep 28
~50% chance of frost before
Growing season
137 days
frost-free stretch
USDA zone
≈ 5a
estimated from nearby reference
Risky (1 year in 10)MedianSafe (9 years in 10)
Last spring frost May 2 May 14 May 27
First fall frost Oct 12 Sep 28 Sep 13
Hard freeze (28°F), median last May 3 · first Oct 5

Computed from NOAA 1991–2020 climate normals at the BIDDLE 8 SW 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 Biddle 8 SW

Computed from Biddle 8 SW's own frost dates. Click any crop for the full zone-5 growing guide — varieties, spacing, fall plantings, and more.

CropStart seeds indoorsTransplantDirect sow
🍅 Tomatoes Mar 19 – Apr 2 May 21 – May 28
🫑 Peppers Mar 5 – Mar 19 May 28 – Jun 4
🥬 Lettuce Apr 2 – Apr 16 Apr 16 – Apr 30 Apr 16 – May 14
🫛 Peas Apr 2 – Apr 16
🥕 Carrots Apr 23 – May 14
🥦 Broccoli Mar 26 – Apr 9 Apr 23 – May 7
🥬 Kale Apr 2 – Apr 16 Apr 16 – Apr 30 Apr 16 – Apr 30
🥒 Cucumbers Apr 16 – Apr 23 May 21 – May 28 May 21 – May 28
🥒 Zucchini Apr 16 – Apr 23 May 21 – May 28 May 21 – May 28
🫘 Green Beans (Bush) May 21 – May 28
🌽 Sweet Corn May 21 – May 28
🌿 Basil Apr 2 – Apr 16 May 21 – May 28 May 28 – Jun 4
🧄 Garlic Fall: Aug 17 – Sep 14

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 Biddle 8 SW's dates automatically after a lookup.

Reading the season in Biddle 8 SW

At about 137 frost-free days, Biddle 8 SW 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 Biddle 8 SW, MT?

The average last spring frost in Biddle 8 SW is around May 14, 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 Biddle 8 SW, MT?

The average first fall frost in Biddle 8 SW arrives around Sep 28. 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 Biddle 8 SW?

About 137 frost-free days on average, from May 14 to Sep 28. 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 Biddle 8 SW in?

USDA zone 5a 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.