Flagstaff, AZ Frost Dates & Growing Season

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

Last spring frost
Jun 4
~50% chance of frost after
First fall frost
Sep 28
~50% chance of frost before
Growing season
116 days
frost-free stretch
USDA zone
6a
2023 hardiness map
Risky (1 year in 10)MedianSafe (9 years in 10)
Last spring frost May 21 Jun 4 Jun 19
First fall frost Oct 9 Sep 28 Sep 16
Hard freeze (28°F), median last May 20 · first Oct 9

Computed from NOAA 1991–2020 climate normals at the Flagstaff Pulliam Airport station (6 km from central Flagstaff). "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 Flagstaff

Computed from Flagstaff'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 Apr 9 – Apr 23 Jun 11 – Jun 18
🫑 Peppers Mar 26 – Apr 9 Jun 18 – Jun 25
🥬 Lettuce Apr 23 – May 7 May 7 – May 21 May 7 – Jun 4
🫛 Peas Apr 23 – May 7
🥕 Carrots May 14 – Jun 4
🥦 Broccoli Apr 16 – Apr 30 May 14 – May 28
🥬 Kale Apr 23 – May 7 May 7 – May 21 May 7 – May 21
🥒 Cucumbers May 7 – May 14 Jun 11 – Jun 18 Jun 11 – Jun 18
🥒 Zucchini May 7 – May 14 Jun 11 – Jun 18 Jun 11 – Jun 18
🫘 Green Beans (Bush) Jun 11 – Jun 18
🌽 Sweet Corn Jun 11 – Jun 18
🌿 Basil Apr 23 – May 7 Jun 11 – Jun 18 Jun 18 – Jun 25
🧄 Garlic Fall: Aug 17 – Sep 14

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 Flagstaff's dates automatically after a lookup.

Reading the season in Flagstaff

At about 116 frost-free days, Flagstaff 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 Flagstaff, AZ?

The average last spring frost in Flagstaff is around Jun 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 Flagstaff, AZ?

The average first fall frost in Flagstaff arrives around Sep 28. 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 Flagstaff?

About 116 frost-free days on average, from Jun 4 to Sep 28. 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 Flagstaff 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.