Lewistown 42 WSW, MT Frost Dates & Growing Season

The two dates every Lewistown 42 WSW garden is planned around, plus ready-computed planting windows for the most popular crops.

Last spring frost
Jun 15
~50% chance of frost after
First fall frost
Sep 4
~50% chance of frost before
Growing season
81 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 31 Jun 15 Jul 8
First fall frost Sep 18 Sep 4 Aug 19
Hard freeze (28°F), median last May 25 · first Sep 18

Computed from NOAA 1991–2020 climate normals at the LEWISTOWN 42 WSW 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 Lewistown 42 WSW

Computed from Lewistown 42 WSW'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 Apr 20 – May 4 Jun 22 – Jun 29
🫑 Peppers Apr 6 – Apr 20 Jun 29 – Jul 6
🥬 Lettuce May 4 – May 18 May 18 – Jun 1 May 18 – Jun 15
🫛 Peas May 4 – May 18
🥕 Carrots May 25 – Jun 15
🥦 Broccoli Apr 27 – May 11 May 25 – Jun 8
🥬 Kale May 4 – May 18 May 18 – Jun 1 May 18 – Jun 1
🥒 Cucumbers May 18 – May 25 Jun 22 – Jun 29 Jun 22 – Jun 29
🥒 Zucchini May 18 – May 25 Jun 22 – Jun 29 Jun 22 – Jun 29
🫘 Green Beans (Bush) Jun 22 – Jun 29
🌽 Sweet Corn Jun 22 – Jun 29
🌿 Basil May 4 – May 18 Jun 22 – Jun 29 Jun 29 – Jul 6
🧄 Garlic Fall: Jul 24 – Aug 21

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 Lewistown 42 WSW's dates automatically after a lookup.

Reading the season in Lewistown 42 WSW

At about 81 frost-free days, Lewistown 42 WSW 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 Lewistown 42 WSW, MT?

The average last spring frost in Lewistown 42 WSW is around Jun 15, 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 Lewistown 42 WSW, MT?

The average first fall frost in Lewistown 42 WSW arrives around Sep 4. 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 Lewistown 42 WSW?

About 81 frost-free days on average, from Jun 15 to Sep 4. 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 Lewistown 42 WSW 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.