Twin Bridges, MT Frost Dates & Growing Season

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

Last spring frost
Jun 8
~50% chance of frost after
First fall frost
Sep 2
~50% chance of frost before
Growing season
86 days
frost-free stretch
USDA zone
≈ 5b
estimated from nearby reference
Risky (1 year in 10)MedianSafe (9 years in 10)
Last spring frost May 22 Jun 8 Jul 1
First fall frost Sep 15 Sep 2 Aug 16
Hard freeze (28°F), median last May 20 · first Sep 15

Computed from NOAA 1991–2020 climate normals at the TWIN BRIDGES 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 Twin Bridges

Computed from Twin Bridges'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 Apr 13 – Apr 27 Jun 15 – Jun 22
🫑 Peppers Mar 30 – Apr 13 Jun 22 – Jun 29
🥬 Lettuce Apr 27 – May 11 May 11 – May 25 May 11 – Jun 8
🫛 Peas Apr 27 – May 11
🥕 Carrots May 18 – Jun 8
🥦 Broccoli Apr 20 – May 4 May 18 – Jun 1
🥬 Kale Apr 27 – May 11 May 11 – May 25 May 11 – May 25
🥒 Cucumbers May 11 – May 18 Jun 15 – Jun 22 Jun 15 – Jun 22
🥒 Zucchini May 11 – May 18 Jun 15 – Jun 22 Jun 15 – Jun 22
🫘 Green Beans (Bush) Jun 15 – Jun 22
🌽 Sweet Corn Jun 15 – Jun 22
🌿 Basil Apr 27 – May 11 Jun 15 – Jun 22 Jun 22 – Jun 29
🧄 Garlic Fall: Jul 22 – Aug 19

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 Twin Bridges's dates automatically after a lookup.

Reading the season in Twin Bridges

At about 86 frost-free days, Twin Bridges 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 Twin Bridges, MT?

The average last spring frost in Twin Bridges is around Jun 8, 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 Twin Bridges, MT?

The average first fall frost in Twin Bridges arrives around Sep 2. 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 Twin Bridges?

About 86 frost-free days on average, from Jun 8 to Sep 2. 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 Twin Bridges in?

USDA zone 5b 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.