Seibert, CO Frost Dates & Growing Season

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

Last spring frost
May 4
~50% chance of frost after
First fall frost
Oct 11
~50% chance of frost before
Growing season
160 days
frost-free stretch
USDA zone
≈ 6a
estimated from nearby reference
Risky (1 year in 10)MedianSafe (9 years in 10)
Last spring frost Apr 22 May 4 May 17
First fall frost Oct 22 Oct 11 Sep 25
Hard freeze (28°F), median last Apr 25 · first Oct 19

Computed from NOAA 1991–2020 climate normals at the SEIBERT 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 Seibert

Computed from Seibert's own frost dates. Click any crop for the full zone-6 growing guide — varieties, spacing, fall plantings, and more.

CropStart seeds indoorsTransplantDirect sow
🍅 Tomatoes Mar 9 – Mar 23 May 11 – May 18
🫑 Peppers Feb 23 – Mar 9 May 18 – May 25
🥬 Lettuce Mar 23 – Apr 6 Apr 6 – Apr 20 Apr 6 – May 4
🫛 Peas Mar 23 – Apr 6
🥕 Carrots Apr 13 – May 4
🥦 Broccoli Mar 16 – Mar 30 Apr 13 – Apr 27
🥬 Kale Mar 23 – Apr 6 Apr 6 – Apr 20 Apr 6 – Apr 20
🥒 Cucumbers Apr 6 – Apr 13 May 11 – May 18 May 11 – May 18
🥒 Zucchini Apr 6 – Apr 13 May 11 – May 18 May 11 – May 18
🫘 Green Beans (Bush) May 11 – May 18
🌽 Sweet Corn May 11 – May 18
🌿 Basil Mar 23 – Apr 6 May 11 – May 18 May 18 – May 25
🧄 Garlic Fall: Aug 30 – Sep 27

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 Seibert's dates automatically after a lookup.

Reading the season in Seibert

Roughly 160 frost-free days gives Seibert gardeners room for nearly every common vegetable. Warm-season crops go out after May 4; a fall garden sown in late summer matures comfortably before the Oct 11 frost.

Frequently asked questions

When is the last frost in Seibert, CO?

The average last spring frost in Seibert is around May 4, 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 Seibert, CO?

The average first fall frost in Seibert arrives around Oct 11. 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 Seibert?

About 160 frost-free days on average, from May 4 to Oct 11. That fits nearly all common vegetables, though the longest-season melons and sweet potatoes benefit from transplants.

What USDA zone is Seibert in?

USDA zone 6a 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.