Frost dates Arizona Phoenix

Frost dates in Phoenix, Arizona

Last spring frost Jan 5 First freeze of winter Jan 3 NOAA 1991-2020

The average last spring frost in Phoenix is Jan 5 and the average first freeze of winter is Jan 3, measured at PHOENIX SKY HARBOR INTL AP, about 4 miles from the city centre. Below: how sure those dates are, and what to start, sow and set out each week.

Average last spring frostJan 532°F, 50% probability
Average first freeze of winterJan 332°F, 50% probability

Winters are mild here: the first freeze of the cold season usually comes after New Year (Jan 3), close to the last one (Jan 5), so there is no frost-free season to count. Frost matters for a few weeks in midwinter only.

How sure is that date? NOAA probability levels for a 32°F freeze
ProbabilityFreeze still comes after (spring)First freeze has come by (winter)
90%Dec 19Jan 21
50%Jan 5Jan 3
10%Jan 22Dec 18

Read it like this: in half of years the last 32°F freeze of spring comes after Jan 5, and in 1 year in 10 there is still a freeze after Jan 22. In 1 year in 10 the first freeze of the cold season arrives before Dec 18.

Measured at: PHOENIX SKY HARBOR INTL AP, AZ (NOAA station USW00023183), about 4 miles away at 1,107 ft, 29 years of record in 1991-2020.

Other stations nearby, for comparison:

  • SOUTH PHOENIX, AZ (NOAA station USC00028112), about 5 miles away at 1,155 ft, 17 years of record in 1991-2020: last spring frost Jan 21, first fall frost Dec 16
  • LAVEEN 3 SSE, AZ (NOAA station USC00024829), about 9 miles away at 1,135 ft, 22 years of record in 1991-2020: last spring frost Jan 14, first fall frost Dec 22

Seed-starting schedule for Phoenix, AZ

Counted from a last frost date of Jan 5 (the average: a freeze comes later than this in half of years).

  1. Week of Sep 2914 weeks before last frost
    • Start seeds indoorsLeekSep 29 to Oct 13
    • Start seeds indoorsOnionSep 29 to Oct 13
  2. Week of Oct 613 weeks before last frost
    • Start seeds indoorsParsleyOct 6 to Oct 13
  3. Week of Oct 1312 weeks before last frost
    • Start seeds indoorsCeleryOct 13 to Oct 27
    • Start seeds indoorsSpinachOct 13 to Oct 27
  4. Week of Oct 2710 weeks before last frost
    • Start seeds indoorsBroccoliOct 27 to Nov 10
    • Start seeds indoorsBrussels sproutOct 27 to Nov 10
    • Start seeds indoorsCabbageOct 27 to Nov 10
    • Start seeds indoorsKaleOct 27 to Nov 10
    • Start seeds indoorsKohlrabiOct 27 to Nov 10
  5. Week of Nov 39 weeks before last frost
    • Start seeds indoorsLettuceNov 3 to Nov 10
  6. Week of Nov 108 weeks before last frost
    • Start seeds indoorsCauliflowerNov 10 to Nov 24
    • Start seeds indoorsEggplantNov 10 to Nov 24
    • Start seeds indoorsPepperNov 10 to Nov 24
    • Start seeds indoorsSwiss chardNov 10 to Nov 24
  7. Week of Nov 177 weeks before last frost
    • Start seeds indoorsTomatoNov 17 to Dec 1
  8. Week of Nov 246 weeks before last frost
    • Start seeds indoorsBasilNov 24 to Dec 8
    • Set transplants outSpinachNov 24 to Dec 15
  9. Week of Dec 84 weeks before last frost
    • Sow seed outdoorsRadishDec 8 to Dec 22
    • Sow seed outdoorsSwiss chardfrom Dec 8
    • Sow seed outdoorsTurnipDec 8 to Dec 22
    • Set transplants outBroccoliDec 8 to Dec 22
    • Set transplants outBrussels sproutDec 8 to Dec 22
    • Set transplants outCabbagefrom Dec 8
    • Set transplants outKalefrom Dec 8
    • Set transplants outKohlrabifrom Dec 8
    • Set transplants outLeekfrom Dec 8
    • Set transplants outLettuceDec 8 to Dec 15
    • Set transplants outOnionfrom Dec 8
  10. Week of Dec 153 weeks before last frost
    • Start seeds indoorsCucumberDec 15 to Dec 22
    • Set transplants outParsleyDec 15 to Dec 22
  11. Week of Dec 222 weeks before last frost
    • Start seeds indoorsMelonDec 22 to Dec 29
    • Start seeds indoorsPumpkinDec 22 to Dec 29
    • Start seeds indoorsSummer squashDec 22 to Dec 29
    • Start seeds indoorsWinter squashDec 22 to Dec 29
    • Start seeds indoorsZucchiniDec 22 to Dec 29
    • Plant seed potatoes outdoorsPotatoDec 22 to Dec 29
    • Set transplants outCauliflowerfrom Dec 22
    • Set transplants outSwiss chardfrom Dec 22
  12. Week of Jan 5Last frost week
    • Sow seed outdoorsBeanfrom Jan 5
    • Sow seed outdoorsParsnipfrom Jan 5
    • Set transplants outCeleryfrom Jan 5
  13. Week of Jan 121 week after last frost
    • Plant slips outdoorsSweet potatoJan 12 to Jan 19
    • Set transplants outCucumberJan 12 to Jan 19
    • Set transplants outTomatoJan 12 to Jan 19
  14. Week of Jan 192 weeks after last frost
    • Set transplants outBasilfrom Jan 19
    • Set transplants outEggplantJan 19 to Jan 26
    • Set transplants outMelonfrom Jan 19
    • Set transplants outPepperfrom Jan 19
    • Set transplants outPumpkinfrom Jan 19
    • Set transplants outSummer squashfrom Jan 19
    • Set transplants outWinter squashfrom Jan 19
    • Set transplants outZucchinifrom Jan 19

Not in the city centre? Look up your own ZIP code

More in Arizona

Where the numbers come from

Sources and method

Frost dates. U.S. Climate Normals 2020: U.S. Annual/Seasonal Climate Normals (1991-2020), NOAA National Centers for Environmental Information (Palecki, Durre, Applequist, Arguez and Lawrimore, 2021). These are 30-year station statistics for 1991 to 2020. "Frost" here means an air temperature of 32°F or lower at the station. We use 6,539 stations that have at least 10 years of record and a published date; 176 more are stations where a freeze is too rare for NOAA to date, and 180 are stations cold enough to have frost risk all year.

Probability level. The headline dates are NOAA's 50% level: in half of years the last spring freeze comes later than that date, and in half of years the first fall freeze comes earlier. The 10% and 90% levels are shown next to them. For tender plants, the 10% spring date is the safer one to plan from: a freeze follows it in only 1 year in 10.

Which station. Your ZIP code is matched to the nearest of those stations by straight-line distance from the ZIP code's centre point (GeoNames, geonames.org, CC BY 4.0; 40,979 ZIP codes in the 50 states and DC). Nearest is not always most alike: a station on a hill, in a valley or by the water can differ from your garden by a week or more. That is why the station's name, distance and elevation are shown with every result, along with two more stations nearby. NOAA makes the same point: the normals are limited between stations as distance grows horizontally and vertically.

Seed-starting offsets. Growing Vegetables: When to Plant Your Vegetable Garden, a fact sheet from University of New Hampshire Extension. It gives each crop's weeks from seed to transplant and when it is safe to set out or sow relative to the last frost. The method is theirs too: take the planting date and count back the seed-to-transplant weeks. Where the fact sheet gives a range of planting dates, the start-indoors dates count back from the earliest one. The figures used, as the fact sheet states them:

  • Basil: Seed to transplant 6-8 weeks; set out 2 weeks after last frost.
  • Bean: Plant seed in garden after last frost.
  • Broccoli: Seed to transplant 4-6 weeks; set out 2-4 weeks before last frost.
  • Brussels sprout: Seed to transplant 4-6 weeks; set out 2-4 weeks before last frost.
  • Cabbage: Seed to transplant 4-6 weeks; set out 4 weeks before last frost.
  • Cauliflower: Seed to transplant 4-6 weeks; set out 2 weeks before last frost.
  • Celery: Seed to transplant 10-12 weeks; set out after last frost.
  • Cucumber: Seed to transplant 3-4 weeks; set out 1-2 weeks after last frost.
  • Eggplant: Seed to transplant 8-10 weeks; set out 2-3 weeks after last frost.
  • Kale: Seed to transplant 4-6 weeks; set out 4 weeks before last frost.
  • Kohlrabi: Seed to transplant 4-6 weeks; set out 4 weeks before last frost.
  • Leek: Seed to transplant 8-10 weeks; set out 4 weeks before last frost.
  • Lettuce: Seed to transplant 4-5 weeks; set out 3-4 weeks before last frost.
  • Melon: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.
  • Onion: Seed to transplant 8-10 weeks; set out 4 weeks before last frost.
  • Parsley: Seed to transplant 9-10 weeks; set out 2-3 weeks before last frost.
  • Parsnip: Plant seed in garden after last frost.
  • Pepper: Seed to transplant 8-10 weeks; set out 2 weeks after last frost.
  • Potato: Plant seed potatoes in garden 1-2 weeks before last frost.
  • Pumpkin: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.
  • Radish: Plant seed in garden 2-4 weeks before last frost.
  • Spinach: Seed to transplant 4-6 weeks; set out 3-6 weeks before last frost.
  • Summer squash: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.
  • Sweet potato: Plant slips in garden 1-2 weeks after last frost.
  • Swiss chard: Seed to transplant 4-6 weeks; set out 2 weeks before last frost; or plant seed in garden 4 weeks before last frost.
  • Tomato: Seed to transplant 6-8 weeks; set out 1-2 weeks after last frost.
  • Turnip: Plant seed in garden 2-4 weeks before last frost.
  • Winter squash: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.
  • Zucchini: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.

Not on the calendar. The same fact sheet times these by soil temperature, not by frost date, so they get no date here:

  • Pea: as soon as the soil thaws.
  • Beet: when the soil warms to 45°F.
  • Carrot: when the soil warms to 60°F.
  • Corn: when the soil warms to 60°F.
  • Cucumber, pumpkin, summer squash, winter squash, zucchini: direct-sow when the soil warms to 70°F.

Rutabaga is left out: the fact sheet gives it New Hampshire calendar dates, not a frost offset.

The fact sheet was written for New Hampshire. The offsets are relative to the last frost, so they carry to other places with a spring frost, but where winters are mild many cool-season crops are grown in fall and winter instead. Your state's extension service has the local calendar. Dates are 30-year statistics, not a forecast: check the forecast before setting tender plants out.

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