Alder 17 S, MT Frost Dates & Growing Season

The two dates every Alder 17 S garden is planned around, plus ready-computed planting windows for the most popular crops.

Last spring frost
Jun 6
~50% chance of frost after
First fall frost
Sep 14
~50% chance of frost before
Growing season
100 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 20 Jun 6 Jun 25
First fall frost Sep 27 Sep 14 Aug 31
Hard freeze (28°F), median last May 16 · first Sep 26

Computed from NOAA 1991–2020 climate normals at the ALDER 17 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 Alder 17 S

Computed from Alder 17 S'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 11 – Apr 25 Jun 13 – Jun 20
🫑 Peppers Mar 28 – Apr 11 Jun 20 – Jun 27
🥬 Lettuce Apr 25 – May 9 May 9 – May 23 May 9 – Jun 6
🫛 Peas Apr 25 – May 9
🥕 Carrots May 16 – Jun 6
🥦 Broccoli Apr 18 – May 2 May 16 – May 30
🥬 Kale Apr 25 – May 9 May 9 – May 23 May 9 – May 23
🥒 Cucumbers May 9 – May 16 Jun 13 – Jun 20 Jun 13 – Jun 20
🥒 Zucchini May 9 – May 16 Jun 13 – Jun 20 Jun 13 – Jun 20
🫘 Green Beans (Bush) Jun 13 – Jun 20
🌽 Sweet Corn Jun 13 – Jun 20
🌿 Basil Apr 25 – May 9 Jun 13 – Jun 20 Jun 20 – Jun 27
🧄 Garlic Fall: Aug 3 – Aug 31

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 Alder 17 S's dates automatically after a lookup.

Reading the season in Alder 17 S

At about 100 frost-free days, Alder 17 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 Alder 17 S, MT?

The average last spring frost in Alder 17 S is around Jun 6, 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 Alder 17 S, MT?

The average first fall frost in Alder 17 S arrives around Sep 14. 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 Alder 17 S?

About 100 frost-free days on average, from Jun 6 to Sep 14. 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 Alder 17 S 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.