USDA Hardiness Zone 9a
Frost Dates for 85746 — Tucson, Arizona
NOAA 1991–2020 normals from Tucson International Airport, AZ (2,549 ft), 5 miles east.
Updated
In Tucson, the last spring frost (32°F) is around February 5 in half of years and has passed by March 2 in nine years out of ten. The first fall frost comes around December 9, as early as November 21 one year in ten, leaving a typical freeze-free season of 307 days (NOAA, Tucson International Airport, AZ).
- Last spring frost
- February 5
- First fall frost
- December 9
- Growing season
- 307 days
- Hardiness zone
- 9a
50% probability
50% probability
freeze-free, 50%
20 to 25°F (-6.7 to -3.9°C) coldest night
- First snow
- Rare
- Last snow
- Rare
- Winters with snow
- 13%
- Snow per year
- 0.1"
median, 1991–2020
median, 1991–2020
4 of 30 observed
NOAA normal
Frost risk by date in Tucson
Half of springs at Tucson International Airport, AZ see their last 32°F night by February 5; only one in ten is past it by January 4, and one in ten still has one after March 2. Planting tender crops after February 17 leaves a 30% risk of a frost on them, after February 23 20%, and after March 2 10%. The 25 days between the even-odds date and the one-in-ten date is wider than at 63% 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 9 in half of years, as early as November 21 one year in ten, and holds off past January 3 one year in ten. A hard freeze of 28°F follows 17 days later, around December 26; in spring the one-in-ten date for 28°F is February 17, 13 days before the 32°F one. The freeze-free season lasts 307 days in a typical year, longer than at 76% of the 98 Arizona stations; it reaches 344 days one year in ten and falls short of 274 one year in ten. On average 12 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 February 28, and return around November 26. A 24°F night is unusual: 19% of winters had one.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Feb 3 | Feb 13 | Feb 19 | Feb 25 | Feb 28 | Mar 3 | Mar 7 | Mar 12 | Mar 24 |
| 32°F99% of yrs | Jan 4 | Jan 14 | Jan 23 | Jan 31 | Feb 5 | Feb 11 | Feb 17 | Feb 23 | Mar 2 |
| 28°F70% of yrs | Dec 14 | Dec 24 | Jan 1 | Jan 5 | Jan 11 | Jan 19 | Jan 31 | Feb 6 | Feb 17 |
| 24°F19% 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 11 | Nov 17 | Nov 20 | Nov 23 | Nov 26 | Nov 30 | Dec 3 | Dec 8 | Dec 14 |
| 32°F99% of yrs | Nov 21 | Nov 26 | Nov 30 | Dec 5 | Dec 9 | Dec 13 | Dec 17 | Dec 24 | Jan 3 |
| 28°F70% of yrs | Nov 30 | Dec 9 | Dec 14 | Dec 20 | Dec 26 | Jan 1 | Jan 6 | Jan 18 | Feb 1 |
| 24°F19% of yrs | too rare for a date | ||||||||
| 20°F3% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Tucson International Airport, 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 85746 →Compare Tucson with another place →
Weather by month in Tucson
July is the warmest month at Tucson International Airport, AZ, averaging 100°F by day and 76°F at night; December is the coldest at 66°F and 41°F. From April to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 51% of years and March still brings one in 11% of years.
Warmth for growing adds up to 7,673 growing degree days a year (base 50°F), more than at 71% of the 102 Arizona stations. 41% of them (3,171) have built up by the end of June, and July adds the most, 1,186. Precipitation totals 10.6 inches a year, most in July (2.2") and least in April (0.2"); May to September bring 56% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 67 | 41 | 0.8 | 80% | 4 | 147 |
| Feb | 69 | 43 | 0.8 | 51% | 2 | 192 |
| Mar | 76 | 48 | 0.6 | 11% | <1 | 373 |
| Apr | 83 | 53 | 0.2 | 0% | 0 | 544 |
| May | 92 | 62 | 0.2 | 0% | 0 | 831 |
| Jun | 101 | 71 | 0.2 | 0% | 0 | 1084 |
| Jul | 100 | 76 | 2.2 | 0% | 0 | 1186 |
| Aug | 99 | 75 | 2.0 | 0% | 0 | 1144 |
| Sep | 95 | 70 | 1.3 | 0% | 0 | 982 |
| Oct | 86 | 59 | 0.7 | 0% | <1 | 702 |
| Nov | 75 | 48 | 0.6 | 30% | 1 | 352 |
| Dec | 66 | 41 | 1.0 | 82% | 5 | 136 |
Monthly normals 1991–2020 at Tucson International Airport, AZ (2,549 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, 9 miles northeast of Tucson, has a last frost 16 days earlier (January 20), a first frost 8 days later (December 17), a season 25 days longer.
When it snows in Tucson, Arizona
Measurable snow is rare here: only 4 of 30 winters from 1991 to 2020 recorded 0.1 inch or more at Tucson International Airport, AZ, 5.3 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 85746
| When | What to do |
|---|---|
| November 27 – December 11 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| December 11 – December 25 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| January 8 – January 22 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| February 5 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by September 16 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by November 25 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| December 9 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 85746 is 5 miles from Tucson International Airport, AZ, which stands at 2,549 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 5 other ZIP codes share the station; its figures are presented in full for 85706 (Tucson). The 2023 USDA Plant Hardiness Zone Map lists ZIP 85746 in zone 9a, the band where the coldest night of the year averaged 20 to 25°F (-6.7 to -3.9°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.