When is the last frost in Flagstaff, AZ?

The average (50% probability) last spring frost in Flagstaff is June 4, based on NOAA 1991–2020 normals. A 1-in-10 risk remains until June 19.

When is the first frost in Flagstaff?

The average first fall frost in Flagstaff is September 28, with a growing season of about 115 days.

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Flagstaff, Arizona frost dates

Average last spring frost: June 4. Average first fall frost: September 28. That gives a growing season of about 115 days. For frost-tender plants, a safer planting date is June 19, after which a freeze happens in only 1 year in 10.

Last frost (50%)

Jun 4

1-in-10 risk after Jun 19

First frost (50%)

Sep 28

1-in-10 risk before Sep 16

Growing season

115 days

median frost-free days

Hard freeze (28°F)

May 20

median last 28°F in spring

Frost risk by date

Chance of frost	Spring: frost after	Fall: frost before
90%	May 21	October 9
70%	May 30	October 2
50%	June 4	September 28
30%	June 10	September 23
10%	June 19	September 16

Read the spring column like this: there is a 10% chance of a 32°F freeze after June 19. These are NOAA probabilities for the Flagstaff Pulliam Airport weather station (USW00003103, elevation 2135 m), 1991–2020.

Flagstaff vegetable planting calendar

Dates count from the 50% last-frost date (June 4). For tomatoes, peppers and other frost-tender crops, waiting until the 10% date (Jun 19) is the cautious choice.

Crop	Start seeds indoors	Plant out
Beans	May 14	Jun 11 (usually sown directly in the garden)
Broccoli	Mar 26	May 7
Brussels sprouts	Mar 26	May 7
Cabbage	Mar 19	Apr 30
Cauliflower	Apr 9	May 21
Sweet corn	May 7	Jun 4 (usually sown directly in the garden)
Cucumbers	May 21	Jun 11
Kale	Mar 19	Apr 30
Leeks	Feb 19	Apr 30
Lettuce	Apr 16	May 21
Melons	May 28	Jun 18
Onions	Feb 12	Apr 23 (from seed; sets and transplants go out at the same time)
Peas	Apr 9	May 7 (usually sown directly in the garden)
Peppers	Apr 23	Jun 18
Squash	May 28	Jun 18
Tomatoes	Apr 9	Jun 4

Offsets from Oregon State University Extension's seed-starting table. "Plant out" means transplant, or sow directly for crops usually grown from seed.

Fall frost and season extension

The first fall freeze usually arrives around September 28. There's a 1-in-10 chance it comes before September 16. Harvest tender crops such as basil, tomatoes, peppers and squash before then, or cover them on cold nights. Cool-season crops like kale, cabbage and Brussels sprouts handle light frost, and often taste sweeter after it. A hard freeze (28°F) typically comes around October 9.

Nearby cities

City	Last frost (50%)	First frost (50%)	Distance
Phoenix, AZ	Jan 5	Jan 3	~193 km
Las Vegas, NV	Jan 20	Dec 15	~334 km
Tucson, AZ	Feb 5	Dec 9	~341 km
Albuquerque, NM	Apr 6	Nov 3	~459 km
Santa Fe, NM	May 4	Oct 15	~509 km
Grand Junction, CO	Apr 28	Oct 16	~526 km

More: all Arizona frost dates