Opheim 10 N, MT Frost Dates & Growing Season

The two dates every Opheim 10 N garden is planned around, plus ready-computed planting windows for the most popular crops.

Last spring frost
Jun 1
~50% chance of frost after
First fall frost
Sep 7
~50% chance of frost before
Growing season
98 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 20 Jun 1 Jun 18
First fall frost Sep 21 Sep 7 Aug 24
Hard freeze (28°F), median last May 21 · first Sep 19

Computed from NOAA 1991–2020 climate normals at the OPHEIM 10 N 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 Opheim 10 N

Computed from Opheim 10 N'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 6 – Apr 20 Jun 8 – Jun 15
🫑 Peppers Mar 23 – Apr 6 Jun 15 – Jun 22
🥬 Lettuce Apr 20 – May 4 May 4 – May 18 May 4 – Jun 1
🫛 Peas Apr 20 – May 4
🥕 Carrots May 11 – Jun 1
🥦 Broccoli Apr 13 – Apr 27 May 11 – May 25
🥬 Kale Apr 20 – May 4 May 4 – May 18 May 4 – May 18
🥒 Cucumbers May 4 – May 11 Jun 8 – Jun 15 Jun 8 – Jun 15
🥒 Zucchini May 4 – May 11 Jun 8 – Jun 15 Jun 8 – Jun 15
🫘 Green Beans (Bush) Jun 8 – Jun 15
🌽 Sweet Corn Jun 8 – Jun 15
🌿 Basil Apr 20 – May 4 Jun 8 – Jun 15 Jun 15 – Jun 22
🧄 Garlic Fall: Jul 27 – Aug 24

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 Opheim 10 N's dates automatically after a lookup.

Reading the season in Opheim 10 N

At about 98 frost-free days, Opheim 10 N 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 Opheim 10 N, MT?

The average last spring frost in Opheim 10 N is around Jun 1, 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 Opheim 10 N, MT?

The average first fall frost in Opheim 10 N arrives around Sep 7. 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 Opheim 10 N?

About 98 frost-free days on average, from Jun 1 to Sep 7. 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 Opheim 10 N 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.