USDA Hardiness Zone 9a
Frost Dates for 85755 — Oro Valley, Arizona
NOAA 1991–2020 normals from Catalina Sp, AZ (2,707 ft), 4 miles southeast.
Updated
In Oro Valley, the last spring frost (32°F) is around April 2 in half of years and has passed by April 18 in nine years out of ten. The first fall frost comes around November 11, as early as October 26 one year in ten, leaving a typical freeze-free season of 222 days (NOAA, Catalina Sp, AZ).
- Last spring frost
- April 2
- First fall frost
- November 11
- Growing season
- 222 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
- 0%
- Snow per year
- 0"
median, 1991–2020
median, 1991–2020
0 of 20 observed
NOAA normal
Frost risk by date in Oro Valley
Half of springs at Catalina Sp, AZ see their last 32°F night by April 2; only one in ten is past it by March 16, and one in ten still has one after April 18. Planting tender crops after April 8 leaves a 30% risk of a frost on them, after April 12 20%, and after April 18 10%. The 16 days between the even-odds date and the one-in-ten date is narrower than at 88% of the 98 Arizona stations behind this site's ZIP pages.
In fall the first 32°F night comes by November 11 in half of years, as early as October 26 one year in ten, and holds off past November 29 one year in ten. A hard freeze of 28°F follows 10 days later, around November 21; in spring the one-in-ten date for 28°F is April 1, 17 days before the 32°F one. The freeze-free season lasts 222 days in a typical year, shorter than at 56% of the 98 Arizona stations; it reaches 245 days one year in ten and falls short of 196 one year in ten. On average 67 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 16 days longer, to about April 18, and return around November 1. Nights of 24°F, cold enough to damage hardier plants, come in 100% of winters and 16°F in 34%.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 4 | Apr 8 | Apr 11 | Apr 15 | Apr 18 | Apr 21 | Apr 25 | Apr 30 | May 5 |
| 32°F | Mar 16 | Mar 21 | Mar 26 | Mar 31 | Apr 2 | Apr 5 | Apr 8 | Apr 12 | Apr 18 |
| 28°F | Feb 22 | Mar 2 | Mar 5 | Mar 9 | Mar 12 | Mar 16 | Mar 21 | Mar 27 | Apr 1 |
| 24°F | Jan 24 | Feb 4 | Feb 10 | Feb 15 | Feb 21 | Feb 27 | Mar 3 | Mar 7 | Mar 12 |
| 20°F86% of yrs | Dec 21 | Jan 2 | Jan 10 | Jan 19 | Jan 27 | Feb 2 | Feb 8 | Feb 16 | Feb 26 |
| 16°F34% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 18 | Oct 23 | Oct 27 | Oct 29 | Nov 1 | Nov 4 | Nov 7 | Nov 11 | Nov 17 |
| 32°F | Oct 26 | Oct 31 | Nov 4 | Nov 7 | Nov 11 | Nov 15 | Nov 18 | Nov 23 | Nov 29 |
| 28°F | Nov 3 | Nov 9 | Nov 14 | Nov 18 | Nov 21 | Nov 25 | Nov 30 | Dec 4 | Dec 10 |
| 24°F | Nov 13 | Nov 20 | Nov 25 | Nov 29 | Dec 4 | Dec 9 | Dec 12 | Dec 17 | Dec 25 |
| 20°F86% of yrs | Nov 24 | Dec 1 | Dec 8 | Dec 14 | Dec 19 | Dec 26 | Jan 2 | Jan 16 | Jan 29 |
| 16°F34% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Catalina Sp, 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 85755 →Compare Oro Valley with another place →
Weather by month in Oro Valley
July is the warmest month at Catalina Sp, AZ, averaging 100°F by day and 71°F at night; December is the coldest at 66°F and 31°F. A freezing night is all but certain in every month from November to March (a 90% chance or more). From May to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 53% of years.
Warmth for growing adds up to 6,057 growing degree days a year (base 50°F), more than at 53% of the 102 Arizona stations. 37% of them (2,241) have built up by the end of June, and July adds the most, 1,091.
| Month | High °F | Low °F | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|
| Jan | 67 | 31 | 100% | 20 | 52 |
| Feb | 68 | 32 | 100% | 15 | 77 |
| Mar | 75 | 36 | 98% | 7 | 195 |
| Apr | 82 | 43 | 53% | 2 | 374 |
| May | 91 | 51 | 3% | <1 | 640 |
| Jun | 101 | 60 | 0% | 0 | 904 |
| Jul | 100 | 71 | 0% | 0 | 1091 |
| Aug | 98 | 69 | 0% | 0 | 1038 |
| Sep | 96 | 62 | 0% | 0 | 859 |
| Oct | 87 | 48 | 21% | 1 | 543 |
| Nov | 76 | 38 | 90% | 7 | 225 |
| Dec | 66 | 31 | 100% | 17 | 59 |
Monthly normals 1991–2020 at Catalina Sp, AZ (2,707 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, Tohono Chul, AZ, 8 miles south of Oro Valley and 180 feet lower, has a last frost 35 days earlier (February 26), a first frost 23 days later (December 4), a season 57 days longer.
When it snows in Oro Valley, Arizona
Measurable snow is rare here: only 0 of 20 winters from 1991 to 2020 recorded 0.1 inch or more at Tucson Camp Ave Exp, AZ, 12.4 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 85755
| When | What to do |
|---|---|
| January 22 – February 5 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 5 – February 19 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 5 – March 19 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 2 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by August 19 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by October 28 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| November 11 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 85755 is 4 miles from Catalina Sp, AZ, which stands at 2,707 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 3 other ZIP codes share the station; its figures are presented in full for 85737 (Oro Valley). The 2023 USDA Plant Hardiness Zone Map lists ZIP 85755 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.