USDA Hardiness Zone 9b
Frost Dates for 85745 — Tucson, Arizona
NOAA 1991–2020 normals from Tucson U Of A #1, AZ (2,315 ft), 1 miles northeast.
Updated
In Tucson, the last spring frost (32°F) is around February 11 in half of years and has passed by March 7 in nine years out of ten. The first fall frost comes around December 2, as early as November 16 one year in ten, leaving a typical freeze-free season of 293 days (NOAA, Tucson U Of A #1, AZ).
- Last spring frost
- February 11
- First fall frost
- December 2
- Growing season
- 293 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
- 5%
- Snow per year
- 0"
median, 1991–2020
median, 1991–2020
1 of 22 observed
NOAA normal
Frost risk by date in Tucson
Half of springs at Tucson U Of A #1, AZ see their last 32°F night by February 11; only one in ten is past it by January 16, and one in ten still has one after March 7. Planting tender crops after February 22 leaves a 30% risk of a frost on them, after February 28 20%, and after March 7 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 2 in half of years, as early as November 16 one year in ten, and holds off past December 20 one year in ten. A hard freeze of 28°F follows 13 days later, around December 15; in spring the one-in-ten date for 28°F is February 17, 18 days before the 32°F one. The freeze-free season lasts 293 days in a typical year, longer than at 68% of the 98 Arizona stations; it reaches 326 days one year in ten and falls short of 263 one year in ten. On average 21 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 6, and return around November 22. A 24°F night is unusual: 38% of winters had one.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Feb 12 | Feb 20 | Feb 25 | Mar 2 | Mar 6 | Mar 10 | Mar 16 | Mar 22 | Mar 30 |
| 32°F | Jan 16 | Jan 27 | Feb 2 | Feb 6 | Feb 11 | Feb 16 | Feb 22 | Feb 28 | Mar 7 |
| 28°F91% of yrs | Dec 21 | Dec 30 | Jan 5 | Jan 11 | Jan 18 | Jan 27 | Feb 2 | Feb 8 | Feb 17 |
| 24°F38% of yrs | too rare for a date | ||||||||
| 20°F2% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Nov 4 | Nov 11 | Nov 16 | Nov 18 | Nov 22 | Nov 24 | Nov 27 | Dec 1 | Dec 6 |
| 32°F | Nov 16 | Nov 22 | Nov 26 | Nov 29 | Dec 2 | Dec 5 | Dec 8 | Dec 13 | Dec 20 |
| 28°F91% of yrs | Nov 29 | Dec 3 | Dec 8 | Dec 11 | Dec 15 | Dec 21 | Dec 26 | Jan 2 | Jan 17 |
| 24°F38% of yrs | too rare for a date | ||||||||
| 20°F2% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Tucson U Of A #1, 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 85745 →Compare Tucson with another place →
Weather by month in Tucson
July is the warmest month at Tucson U Of A #1, AZ, averaging 101°F by day and 75°F at night; December is the coldest at 67°F and 39°F. A freezing night is all but certain in every month from December to January (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 67% of years and March still brings one in 20% of years.
Warmth for growing adds up to 7,536 growing degree days a year (base 50°F), more than at 68% of the 102 Arizona stations. 41% of them (3,080) have built up by the end of June, and July adds the most, 1,186. Precipitation totals 10.7 inches a year, most in July (2.0") and least in May (0.2"); May to September bring 51% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 67 | 39 | 1.0 | 95% | 7 | 134 |
| Feb | 71 | 42 | 0.9 | 67% | 3 | 184 |
| Mar | 77 | 46 | 0.6 | 20% | 1 | 363 |
| Apr | 84 | 51 | 0.3 | 0% | 0 | 531 |
| May | 93 | 60 | 0.2 | 0% | 0 | 809 |
| Jun | 102 | 69 | 0.3 | 0% | 0 | 1059 |
| Jul | 101 | 75 | 2.0 | 0% | 0 | 1186 |
| Aug | 100 | 74 | 2.0 | 0% | 0 | 1145 |
| Sep | 96 | 69 | 1.0 | 0% | 0 | 978 |
| Oct | 87 | 57 | 0.7 | 1% | 0 | 685 |
| Nov | 76 | 45 | 0.6 | 44% | 2 | 333 |
| Dec | 67 | 39 | 1.1 | 92% | 9 | 129 |
Monthly normals 1991–2020 at Tucson U Of A #1, AZ (2,315 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, Tucson WFO, AZ, 4 miles east of Tucson, has a last frost 22 days earlier (January 20), a first frost 15 days later (December 17), a season 39 days longer.
When it snows in Tucson, Arizona
Measurable snow is rare here: only 1 of 22 winters from 1991 to 2020 recorded 0.1 inch or more at Tucson U Of A #1, AZ, 1.4 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 85745
| When | What to do |
|---|---|
| December 3 – December 17 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| December 17 – December 31 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| January 14 – January 28 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| February 11 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by September 9 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by November 18 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| December 2 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 85745 is 1 mile from Tucson U Of A #1, AZ, which stands at 2,315 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station; its figures are presented in full for 85705 (Tucson). The 2023 USDA Plant Hardiness Zone Map lists ZIP 85745 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.