Frost Dates for Flagstaff, AZ 86011

Flagstaff has 5 ZIP codes. The Flagstaff, AZ frost page lists all of them with their dates.

Last spring frost June 21 · First fall frost September 9 · 80 frost-free days · USDA Zone 3–4

Frost probability for 86011

Frost10%50%90%
Spring (last frost)July 2June 21June 11
Fall (first frost)August 20September 9September 28

Dates come from NOAA 1971–2000 freeze probabilities at the nearest reporting station (22.4 km away); the 50% date is the median year.

Month by month in Flagstaff

MonthWhat to do
JanuaryPlan your garden layout and order seeds. Research varieties suited to your frost dates.
FebruaryStart the slowest-growing crops indoors: onions, leeks, and celery (10–12 weeks before last frost).
MarchOrganize planting supplies and seed-starting mix. Check stored garden tools.
AprilStart peppers and eggplant indoors 8–10 weeks before your last frost (around June 21). Start tomatoes about two weeks later, 6–8 weeks before last frost.
MayStart herbs, basil, and squash indoors (4–6 weeks before frost). Direct sow peas, spinach, and lettuce if soil is workable.
JuneLast frost around June 21. Transplant cold-hardy crops (broccoli, kale, cabbage). Harden off tomato and pepper seedlings.
JulyFrost has passed. Transplant tomatoes, peppers, and basil outdoors. Direct sow beans, cucumbers, squash, and zucchini.
AugustFirst fall frost approaching (around September 9). Transplant fall brassicas. Sow spinach, arugula, and radishes.
SeptemberFirst frost around September 9. Harvest tomatoes and peppers before frost. Cover cold-hardy crops with row covers to extend the season.
OctoberHarvest remaining cold-hardy crops: kale, carrots, and beets. Plant garlic bulbs for next year.
NovemberClean up spent plants. Add compost to beds. Rest, review, and plan next year's garden.
DecemberClean up spent plants. Add compost to beds. Rest, review, and plan next year's garden.

What grows in a 80-day season

Frequently Asked Questions

What is the last frost date for Flagstaff, AZ (ZIP 86011)?

The median last spring frost date for Flagstaff, AZ (ZIP code 86011) is around June 21. This is the 50th-percentile date — meaning half of all years see frost end before this date. Use the 10% and 90% dates to understand the full range of risk in your area.

What is the first fall frost date in Flagstaff, AZ?

The median first fall frost date for Flagstaff, AZ is around September 9. Plan to harvest or protect frost-sensitive crops like tomatoes and peppers at least a week before this date to avoid losses.

How long is the growing season in Flagstaff, AZ?

The frost-free growing season in Flagstaff is about 80 days. This window — from your last spring frost to your first fall frost — is when warm-season vegetables thrive. Cold-hardy crops like kale, spinach, and peas can extend your season by weeks on either side.

What USDA hardiness zone is Flagstaff, AZ?

Based on frost date patterns, Flagstaff falls approximately in Zone 3–4. USDA hardiness zones are determined by average annual minimum winter temperatures and guide both plant selection and planting timing for your location.

When should I start tomatoes indoors in Flagstaff, AZ?

Start tomato seeds indoors 6–8 weeks before your last frost date (around June 21). For Flagstaff, that's roughly April 26 to May 10. Transplant outdoors 1–2 weeks after your last frost.

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