USDA Hardiness Zone 9b
Frost Dates for 85251 — Scottsdale, Arizona
NOAA 1991–2020 normals from Tempe Asu, AZ (1,167 ft), 5 miles south.
Updated
In Scottsdale, the last spring frost (32°F) is around February 13 in half of years and has passed by March 9 in nine years out of ten. The first fall frost comes around December 5, as early as November 18 one year in ten, leaving a typical freeze-free season of 298 days (NOAA, Tempe Asu, AZ).
- Last spring frost
- February 13
- First fall frost
- December 5
- Growing season
- 298 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
- 0%
- Snow per year
- 0"
median, 1991–2020
median, 1991–2020
0 of 30 observed
NOAA normal
Frost risk by date in Scottsdale
Half of springs at Tempe Asu, AZ see their last 32°F night by February 13; only one in ten is past it by January 12, and one in ten still has one after March 9. Planting tender crops after February 24 leaves a 30% risk of a frost on them, after March 1 20%, and after March 9 10%. The 24 days between the even-odds date and the one-in-ten date is wider than at 58% 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 5 in half of years, as early as November 18 one year in ten, and holds off past December 24 one year in ten. A hard freeze of 28°F follows 14 days later, around December 19; in spring the one-in-ten date for 28°F is February 19, 18 days before the 32°F one. The freeze-free season lasts 298 days in a typical year, longer than at 69% of the 98 Arizona stations; it reaches 331 days one year in ten and falls short of 266 one year in ten. On average 10 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 23 days longer, to about March 8, and return around November 26. A 24°F night is unusual: 32% of winters had one.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Feb 14 | Feb 21 | Feb 27 | Mar 3 | Mar 8 | Mar 12 | Mar 20 | Mar 28 | Apr 7 |
| 32°F | Jan 12 | Jan 23 | Feb 1 | Feb 6 | Feb 13 | Feb 18 | Feb 24 | Mar 1 | Mar 9 |
| 28°F87% of yrs | Dec 19 | Dec 30 | Jan 4 | Jan 10 | Jan 16 | Jan 24 | Feb 1 | Feb 7 | Feb 19 |
| 24°F32% of yrs | too rare for a date | ||||||||
| 20°F3% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Nov 7 | Nov 14 | Nov 18 | Nov 22 | Nov 26 | Nov 29 | Dec 1 | Dec 4 | Dec 9 |
| 32°F | Nov 18 | Nov 24 | Nov 29 | Dec 1 | Dec 5 | Dec 9 | Dec 12 | Dec 16 | Dec 24 |
| 28°F87% of yrs | Nov 27 | Dec 4 | Dec 10 | Dec 14 | Dec 19 | Dec 24 | Dec 30 | Jan 4 | Jan 19 |
| 24°F32% of yrs | too rare for a date | ||||||||
| 20°F3% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Tempe Asu, 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 85251 →Compare Scottsdale with another place →
Weather by month in Scottsdale
July is the warmest month at Tempe Asu, AZ, averaging 106°F by day and 76°F at night; December is the coldest at 69°F and 38°F. A freezing night is all but certain in December (a 90% chance or more). From April to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 64% of years and March still brings one in 20% of years.
Warmth for growing adds up to 8,036 growing degree days a year (base 50°F), more than at 76% of the 102 Arizona stations. 40% of them (3,250) have built up by the end of June, and July adds the most, 1,266. Precipitation totals 8.9 inches a year, most in August (1.3") and least in June (0.1"); May to September bring 37% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 71 | 39 | 1.0 | 87% | 3 | 162 |
| Feb | 74 | 41 | 1.1 | 64% | 2 | 214 |
| Mar | 80 | 46 | 1.0 | 20% | <1 | 408 |
| Apr | 87 | 51 | 0.2 | 2% | 0 | 567 |
| May | 95 | 59 | 0.2 | 0% | 0 | 839 |
| Jun | 104 | 67 | 0.1 | 0% | 0 | 1061 |
| Jul | 106 | 76 | 1.0 | 0% | 0 | 1266 |
| Aug | 105 | 75 | 1.3 | 0% | 0 | 1238 |
| Sep | 101 | 69 | 0.7 | 0% | 0 | 1045 |
| Oct | 91 | 56 | 0.6 | 0% | 0 | 733 |
| Nov | 79 | 45 | 0.7 | 34% | 1 | 365 |
| Dec | 69 | 38 | 1.0 | 92% | 4 | 138 |
Monthly normals 1991–2020 at Tempe Asu, AZ (1,167 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 southwest of Scottsdale, has a 32°F night in 18% of winters against 100% here, and a coolest-month low 7°F warmer (45°F).
When it snows in Scottsdale, Arizona
Measurable snow is rare here: only 0 of 30 winters from 1991 to 2020 recorded 0.1 inch or more at Tempe Asu, AZ, 4.7 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 85251
| When | What to do |
|---|---|
| December 5 – December 19 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| December 19 – January 2 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| January 16 – January 30 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| February 13 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by September 12 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by November 21 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| December 5 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 85251 is 5 miles from Tempe Asu, AZ, which stands at 1,167 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 16 other ZIP codes share the station; its figures are presented in full for 85225 (Chandler). The 2023 USDA Plant Hardiness Zone Map lists ZIP 85251 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.