USDA Hardiness Zone 9b
Frost Dates for 85033 — Phoenix, Arizona
NOAA 1991–2020 normals from Youngtown, AZ (1,135 ft), 9 miles northwest.
Updated
In Phoenix, the last spring frost (32°F) is around January 20 in half of years and has passed by February 18 in nine years out of ten. The first fall frost comes around December 15, as early as November 28 one year in ten, leaving a typical freeze-free season of 331 days (NOAA, Youngtown, AZ).
- Last spring frost
- January 20
- First fall frost
- December 15
- Growing season
- 331 days
- Hardiness zone
- 9b
50% probability
50% probability
freeze-free, 50%
25 to 30°F (-3.9 to -1.1°C) coldest night
- First snow
- Rare
- Last snow
- Rare
- Winters with snow
- 26%
- Snow per year
- 0.2"
median, 1991–2020
median, 1991–2020
5 of 19 observed
NOAA normal
Frost risk by date in Phoenix
Half of springs at Youngtown, AZ see their last 32°F night by January 20; only one in ten is past it by December 23, and one in ten still has one after February 18. Planting tender crops after February 2 leaves a 30% risk of a frost on them, after February 9 20%, and after February 18 10%. The 29 days between the even-odds date and the one-in-ten date is wider than at 79% 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 15 in half of years, as early as November 28 one year in ten, and holds off past January 7 one year in ten. A hard freeze of 28°F is less common: it came in 49% 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 297 one year in ten. On average 4 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 14, and return around December 2. A 24°F night is unusual: 6% of winters had one.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jan 21 | Jan 31 | Feb 4 | Feb 9 | Feb 14 | Feb 18 | Feb 23 | Feb 28 | Mar 4 |
| 32°F95% of yrs | Dec 23 | Dec 31 | Jan 6 | Jan 13 | Jan 20 | Jan 28 | Feb 2 | Feb 9 | Feb 18 |
| 28°F49% of yrs | too rare for a date | ||||||||
| 24°F6% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Nov 17 | Nov 23 | Nov 26 | Nov 29 | Dec 2 | Dec 5 | Dec 8 | Dec 12 | Dec 18 |
| 32°F95% of yrs | Nov 28 | Dec 3 | Dec 8 | Dec 11 | Dec 15 | Dec 19 | Dec 23 | Dec 28 | Jan 7 |
| 28°F49% of yrs | too rare for a date | ||||||||
| 24°F6% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Youngtown, 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 85033 →Compare Phoenix with another place →
Weather by month in Phoenix
July is the warmest month at Youngtown, AZ, averaging 105°F by day and 80°F at night; December is the coldest at 64°F and 40°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 8,100 growing degree days a year (base 50°F), more than at 77% of the 102 Arizona stations. 41% of them (3,291) have built up by the end of June, and July adds the most, 1,311. Precipitation totals 8.3 inches a year, most in February (1.3") and least in June (0.0"); May to September bring 31% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 65 | 41 | 1.0 | 64% | 1 | 129 |
| Feb | 69 | 44 | 1.3 | 31% | 1 | 191 |
| Mar | 77 | 49 | 1.0 | 1% | 0 | 395 |
| Apr | 84 | 55 | 0.3 | 0% | 0 | 584 |
| May | 93 | 64 | 0.1 | 0% | 0 | 876 |
| Jun | 102 | 72 | 0.0 | 0% | 0 | 1116 |
| Jul | 105 | 80 | 0.8 | 0% | 0 | 1311 |
| Aug | 104 | 79 | 1.0 | 0% | 0 | 1283 |
| Sep | 98 | 73 | 0.7 | 0% | 0 | 1063 |
| Oct | 87 | 60 | 0.6 | 0% | 0 | 721 |
| Nov | 74 | 48 | 0.6 | 13% | <1 | 328 |
| Dec | 64 | 40 | 0.9 | 77% | 2 | 102 |
Monthly normals 1991–2020 at Youngtown, AZ (1,135 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, Litchfield Park, AZ, 9 miles west of Phoenix, has a last frost 13 days earlier (January 7), a first frost 9 days later (December 24), a season 20 days longer.
When it snows in Phoenix, Arizona
Measurable snow is rare here: only 5 of 19 winters from 1991 to 2020 recorded 0.1 inch or more at Tolleson 1 E, AZ, 3.5 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 85033
| When | What to do |
|---|---|
| November 11 – November 25 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| November 25 – December 9 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| December 23 – January 6 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| January 20 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by September 22 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by December 1 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| December 15 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 85033 is 9 miles from Youngtown, AZ, which stands at 1,135 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 18 other ZIP codes share the station; its figures are presented in full for 85383 (Peoria). The 2023 USDA Plant Hardiness Zone Map lists ZIP 85033 in zone 9b, the band where the coldest night of the year averaged 25 to 30°F (-3.9 to -1.1°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.