Monument 3S, CO Frost Dates & Growing Season

The two dates every Monument 3S garden is planned around, plus ready-computed planting windows for the most popular crops.

Last spring frost
May 17
~50% chance of frost after
First fall frost
Oct 1
~50% chance of frost before
Growing season
137 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 5 May 17 May 30
First fall frost Oct 12 Oct 1 Sep 19
Hard freeze (28°F), median last May 6 · first Oct 9

Computed from NOAA 1991–2020 climate normals at the MONUMENT 3S 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 Monument 3S

Computed from Monument 3S'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 22 – Apr 5 May 24 – May 31
🫑 Peppers Mar 8 – Mar 22 May 31 – Jun 7
🥬 Lettuce Apr 5 – Apr 19 Apr 19 – May 3 Apr 19 – May 17
🫛 Peas Apr 5 – Apr 19
🥕 Carrots Apr 26 – May 17
🥦 Broccoli Mar 29 – Apr 12 Apr 26 – May 10
🥬 Kale Apr 5 – Apr 19 Apr 19 – May 3 Apr 19 – May 3
🥒 Cucumbers Apr 19 – Apr 26 May 24 – May 31 May 24 – May 31
🥒 Zucchini Apr 19 – Apr 26 May 24 – May 31 May 24 – May 31
🫘 Green Beans (Bush) May 24 – May 31
🌽 Sweet Corn May 24 – May 31
🌿 Basil Apr 5 – Apr 19 May 24 – May 31 May 31 – Jun 7
🧄 Garlic Fall: Aug 20 – Sep 17

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 Monument 3S's dates automatically after a lookup.

Reading the season in Monument 3S

At about 137 frost-free days, Monument 3S 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 Monument 3S, CO?

The average last spring frost in Monument 3S is around May 17, 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 Monument 3S, CO?

The average first fall frost in Monument 3S arrives around Oct 1. 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 Monument 3S?

About 137 frost-free days on average, from May 17 to Oct 1. 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 Monument 3S 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.