USDA Hardiness Zone 10a
Frost Dates for 85009 — Phoenix, Arizona
NOAA 1991–2020 normals from South Phoenix, AZ (1,155 ft), 6 miles southeast.
Updated
In Phoenix, the last spring frost (32°F) is around January 21 in half of years and has passed by February 20 in nine years out of ten. The first fall frost comes around December 16, as early as November 29 one year in ten, leaving a typical freeze-free season of 331 days (NOAA, South Phoenix, AZ).
- Last spring frost
- January 21
- First fall frost
- December 16
- Growing season
- 331 days
- Hardiness zone
- 10a
50% probability
50% probability
freeze-free, 50%
30 to 35°F (-1.1 to 1.7°C) coldest night
- First snow
- Rare
- Last snow
- Rare
- Winters with snow
- 0%
- Snow per year
- 0"
median, 1991–2020
median, 1991–2020
0 of 17 observed
NOAA normal
Frost risk by date in Phoenix
Half of springs at South Phoenix, AZ see their last 32°F night by January 21; only one in ten is past it by December 24, and one in ten still has one after February 20. Planting tender crops after February 3 leaves a 30% risk of a frost on them, after February 11 20%, and after February 20 10%. The 30 days between the even-odds date and the one-in-ten date is wider than at 83% of the 98 Arizona stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.
In fall the first 32°F night comes by December 16 in half of years, as early as November 29 one year in ten, and holds off past January 9 one year in ten. A hard freeze of 28°F is less common: it came in 47% of winters. The freeze-free season lasts 331 days in a typical year, longer than at 86% of the 98 Arizona stations; it reaches 358 days one year in ten and falls short of 295 one year in ten. On average 9 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 25 days longer, to about February 15, and return around December 1. A 24°F night is unusual: 4% of winters had one.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jan 16 | Jan 28 | Feb 3 | Feb 10 | Feb 15 | Feb 20 | Feb 27 | Mar 1 | Mar 7 |
| 32°F94% of yrs | Dec 24 | Jan 2 | Jan 7 | Jan 14 | Jan 21 | Jan 29 | Feb 3 | Feb 11 | Feb 20 |
| 28°F47% of yrs | too rare for a date | ||||||||
| 24°F4% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Nov 16 | Nov 22 | Nov 25 | Nov 29 | Dec 1 | Dec 5 | Dec 8 | Dec 12 | Dec 17 |
| 32°F94% of yrs | Nov 29 | Dec 4 | Dec 8 | Dec 12 | Dec 16 | Dec 20 | Dec 25 | Dec 30 | Jan 9 |
| 28°F47% of yrs | too rare for a date | ||||||||
| 24°F4% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at South Phoenix, AZ, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 85009 →Compare Phoenix with another place →
Weather by month in Phoenix
July is the warmest month at South Phoenix, AZ, averaging 103°F by day and 77°F at night; December is the coldest at 65°F and 41°F. From March to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 31% of years.
Warmth for growing adds up to 7,882 growing degree days a year (base 50°F), more than at 74% of the 102 Arizona stations. 41% of them (3,243) have built up by the end of June, and July adds the most, 1,235. Precipitation totals 7.8 inches a year, most in February (1.0") and least in May (0.1"); May to September bring 31% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 67 | 42 | 0.9 | 66% | 3 | 152 |
| Feb | 71 | 44 | 1.0 | 31% | 1 | 215 |
| Mar | 78 | 48 | 1.0 | 3% | <1 | 404 |
| Apr | 85 | 54 | 0.3 | 0% | 0 | 582 |
| May | 93 | 62 | 0.1 | 0% | 0 | 837 |
| Jun | 101 | 69 | 0.1 | 0% | 0 | 1053 |
| Jul | 103 | 77 | 0.8 | 0% | 0 | 1235 |
| Aug | 101 | 78 | 0.8 | 0% | 0 | 1218 |
| Sep | 97 | 71 | 0.6 | 0% | 0 | 1024 |
| Oct | 87 | 59 | 0.7 | 0% | 0 | 711 |
| Nov | 74 | 48 | 0.7 | 12% | 1 | 332 |
| Dec | 65 | 41 | 0.8 | 73% | 5 | 118 |
Monthly normals 1991–2020 at South Phoenix, AZ (1,155 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, Phoenix Sky Harbor International Airport, AZ, 7 miles east of Phoenix, has a 32°F night in 18% of winters against 94% here, and a coolest-month low 4°F warmer (45°F).
When it snows in Phoenix, Arizona
Measurable snow is rare here: only 0 of 17 winters from 1991 to 2020 recorded 0.1 inch or more at South Phoenix, AZ, 6 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 85009
| When | What to do |
|---|---|
| November 12 – November 26 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| November 26 – December 10 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| December 24 – January 7 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| January 21 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by September 23 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by December 2 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| December 16 onward | Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter. |
The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.
Where these figures come from
ZIP 85009 is 6 miles from South Phoenix, AZ, which stands at 1,155 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 8 other ZIP codes share the station; its figures are presented in full for 85041 (Phoenix). The 2023 USDA Plant Hardiness Zone Map lists ZIP 85009 in zone 10a, the band where the coldest night of the year averaged 30 to 35°F (-1.1 to 1.7°C) over 1991–2020; a zone describes winter lows, not frost dates.
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.