Phoenix, Arizona Frost Dates, Growing Season & Hardiness Zone

When is the last frost in Phoenix?

A freeze isn't guaranteed every year. At Phoenix Deer Valley Municipal Airport, NOAA puts the yearly chance of a 32°F night at 70.2%. Every date on this page is conditional: it describes only the years that reach 32°F.

Counting only years with a freeze, half are past their last 32°F night by Jan 8, and 1 in 10 has one after Feb 12. NOAA puts the yearly chance of a 36°F night (frost possible on plants) at 99.1%, with the last one typically around Feb 1. The yearly chance of a 28°F hard freeze is 17.4%.

In Phoenix, late frosts can come well after the typical date. The safer 1-in-10 date (Feb 12) is 35 days after the typical date (Jan 8). Tender plants set out early will need cover on cold nights.

Cool nights hang on after the last freeze. In years with a freeze, the typical last 32°F night is around Jan 8, and the typical last 36°F night (frost possible on plants in low spots) comes 24 days later, around Feb 1. On clear, calm nights, frost can form on leaves while the thermometer still reads above freezing.

Is it too early to plant in Phoenix?

Before Jan 8 the odds of another 32°F night are better than even; after Feb 12 they are about 1 in 10 or less.

Today's risk is computed in your browser from the same NOAA probability table, shown as the range between the two nearest NOAA probability levels.

When is the first frost in Phoenix?

In the years that freeze, half have their first 32°F night by Dec 25, and 1 in 10 of them has one as early as Dec 5. The first 36°F night (frost possible on plants) typically comes around Dec 11. A 28°F hard freeze comes in 17.4% of years.

Fall plantings are timed backward from first frost: Dec 25 typically, or Dec 5 if you want a cushion. See the planting calendar for each crop's date.

How long is Phoenix's growing season?

Phoenix's frost-free season (32°F) typically runs 354 days. In about 1 year out of 10, it's shorter than 320 days.

This much frost-free time means many crops can go in twice, in spring and again for a fall harvest.

Each year the station logs an average of 8,306 growing degree days (base 50°F), a measure of the heat available for crop growth.

How does Phoenix's season compare?

At 354 days, the typical frost-free season in Phoenix is the longest among the 3 Arizona cities with frost dates on this site.

Among the 56 U.S. cities with frost dates on this site, the typical frost-free season here is longer than in 54 of them and shorter than in 1.

Growing degree days (base 50°F)

Annual normal: 8,306 GDD (NOAA flag R, 20 years). Running total by the end of each month (sum of NOAA daily GDD normals, so the year-end total can differ slightly from the annual normal):

What growing zone is Phoenix? (USDA 2023)

The 2023 USDA map puts Phoenix in zone 9b–10a (25 to 35°F average coldest winter night). On the 2012 map, most of the city was 9b. Comparing ZIPs listed in both tables, 27 of 63 moved up half a zone.

Zones: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed 2026-10-08. Shown as published in the ZIP tables; this page does not show a zone map. Not the official USDA Plant Hardiness Zone Map (official map: planthardiness.ars.usda.gov).

Does the new zone change Phoenix's frost dates?

No. A hardiness zone reflects only the average coldest winter temperature, not the timing of spring or fall frost. Phoenix's frost dates come from NOAA's 1991–2020 frost probabilities, and the 2023 zone map didn't change them. Pick perennials that survive winter by zone; time your planting by frost dates.

Why do Phoenix frost dates differ between websites?

You may see Jan 23 given as the last frost date for Phoenix. That's the 30%-risk date: in years with a freeze, about 3 in 10 have a 32°F night after it. We lead with Jan 8, the 50% (median) date.

Feb 12 is the 10%-risk, or 'safer', date: only about 1 in 10 years with a freeze has a 32°F night after it.

Feb 1 is the typical (50%) date for a 36°F night (frost possible on plants), not a 32°F freeze. Any site that draws the line at 36°F will show later dates.

Sites also pick different weather stations. Within 25 miles of the city center, the 9 stations that meet our quality rules put the typical (50%) last 32°F frost anywhere from Jan 5 to Feb 13 (table below).

Which weather station is this based on?

Station

Phoenix Deer Valley Municipal Airport (NOAA USW00003184, WBAN/ASOS-AWOS)

Distance

8.0 mi N of the city center

Elevation

1,455 ft; city center 1,242 ft (USGS), difference +213 ft

Record

NOAA completeness flag R, 21 of 30 years (1991–2020)

Confidence

High (rule)

Confidence: High. The station is 8.0 miles from the city center, only 213 ft different in elevation, and its frost statistics meet our completeness rule (NOAA flag R, 21 of 30 years).

Caveat: NOAA flags this station's frost statistics 'R' (representative). They rest on 21 of the 30 years in 1991–2020, with missing months filled in from surrounding stations. The nearest station with a full 'S' (standard) record is Phoenix Sky Harbor International Airport, 11.1 mi away; its typical last frost is Jan 5.

Phoenix planting dates at a glance

Balanced dates use the 30%-risk last-frost date as the anchor. The Phoenix planting calendar has typical and safe dates, fall planting and a month-by-month list for 26 vegetables.

When to plant tomatoes in Phoenix · Fall planting dates for Phoenix

Frost dates near Phoenix

All Arizona cities

Frequently asked questions

What is the average last frost date in Phoenix?

Counting only years with a freeze (70.2% of years, NOAA 1991–2020 normals at Phoenix Deer Valley Municipal Airport), the median last 32°F night is Jan 8. For a safer target, use Feb 12; after that, about 1 in 10 of those years still has a freeze.

When is the first frost in Phoenix?

Not every year has one: NOAA's yearly chance of a 32°F night at Phoenix Deer Valley Municipal Airport is 70.2%. In the years with a freeze, the first typically comes by Dec 25; in about 1 in 10 of them, by Dec 5.

What growing zone is Phoenix, Arizona?

Zone 9b–10a. Most of Phoenix was 9b on the 2012 map too, but 27 of 63 city ZIPs changed zone.

Is it too early to plant in Phoenix?

If you plant frost-tender crops before Jan 8, a 32°F night after planting is more likely than not in years with a freeze. For planting days from Jan 8 to Feb 12, that risk falls from 50% to 10% of those years. In any given year, NOAA puts the chance of a 32°F night at Phoenix Deer Valley Municipal Airport at 70.2%. Peas, lettuce and other cool-season crops can go in weeks earlier (see the planting calendar).

What temperature is a killing frost?

A light frost is enough to kill tender crops such as tomatoes. CSU Extension describes 28–32°F as a light frost and anything below 28°F as a heavy frost. We report NOAA odds at three thresholds: 36°F (frost possible on plants), 32°F (freeze, our headline) and 28°F (hard freeze).

Is first frost the same as first freeze?

Not exactly. A freeze is about the air reaching 32°F. Frost is ice on surfaces, which can form on calm, clear nights while the air is still a few degrees above freezing. The first 36°F night (frost possible on plants) in Phoenix typically comes around Dec 11. Freezes don't come every year here: NOAA puts the yearly chance of a 32°F night at 70.2%, and in years that have one, the first typically arrives around Dec 25.

Download & sources

• Add Phoenix frost & planting dates to your calendar (.ics, 2027)
• Printable planting calendar (PDF)
• How these numbers are calculated

Data: NOAA NCEI U.S. Climate Normals 1991–2020 (annual/seasonal and daily normals, station USW00003184); USDA Plant Hardiness Zone ZIP tables 2023 and 2012 by the PRISM Group, Oregon State University; Census 2020 ZIP/place relationship file; USGS elevation. Long-term odds, not a forecast. Figures and sentences are generated from these data by fixed rules; see the methodology. Last updated 2026-10-08.