USDA Hardiness Zone 9a
Frost Dates for 85631 — San Manuel, Arizona
NOAA 1991–2020 normals from San Manuel, AZ (3,420 ft), 2 miles west.
Updated
In San Manuel, the last spring frost (32°F) is around February 4 in half of years and has passed by March 2 in nine years out of ten. The first fall frost comes around December 8, as early as November 20 one year in ten, leaving a typical freeze-free season of 306 days (NOAA, San Manuel, AZ).
- Last spring frost
- February 4
- First fall frost
- December 8
- Growing season
- 306 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
- 45%
- Snow per year
- 0.7"
median, 1991–2020
median, 1991–2020
9 of 20 observed
NOAA normal
Frost risk by date in San Manuel
Half of springs at San Manuel, AZ see their last 32°F night by February 4; only one in ten is past it by January 5, and one in ten still has one after March 2. Planting tender crops after February 16 leaves a 30% risk of a frost on them, after February 23 20%, and after March 2 10%. The 26 days between the even-odds date and the one-in-ten date is wider than at 67% 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 8 in half of years, as early as November 20 one year in ten, and holds off past December 28 one year in ten. A hard freeze of 28°F follows 14 days later, around December 22; in spring the one-in-ten date for 28°F is February 11, 19 days before the 32°F one. The freeze-free season lasts 306 days in a typical year, longer than at 73% of the 98 Arizona stations; it reaches 340 days one year in ten and falls short of 274 one year in ten. On average 14 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 March 1, and return around November 25. A 24°F night is unusual: 22% of winters had one.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Feb 2 | Feb 13 | Feb 19 | Feb 25 | Mar 1 | Mar 6 | Mar 10 | Mar 17 | Mar 30 |
| 32°F | Jan 5 | Jan 13 | Jan 23 | Feb 1 | Feb 4 | Feb 10 | Feb 16 | Feb 23 | Mar 2 |
| 28°F78% of yrs | Dec 17 | Dec 26 | Dec 31 | Jan 5 | Jan 10 | Jan 18 | Jan 29 | Feb 4 | Feb 11 |
| 24°F22% of yrs | too rare for a date | ||||||||
| 20°F1% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Nov 9 | Nov 15 | Nov 19 | Nov 22 | Nov 25 | Nov 29 | Dec 3 | Dec 7 | Dec 11 |
| 32°F | Nov 20 | Nov 26 | Dec 1 | Dec 5 | Dec 8 | Dec 12 | Dec 16 | Dec 20 | Dec 28 |
| 28°F78% of yrs | Dec 3 | Dec 9 | Dec 14 | Dec 18 | Dec 22 | Dec 27 | Jan 1 | Jan 8 | Jan 25 |
| 24°F22% of yrs | too rare for a date | ||||||||
| 20°F1% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at San Manuel, 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 85631 →Compare San Manuel with another place →
Compared with the next station
The nearest other station, Oracle Sp, AZ, 8 miles west of San Manuel and 1,175 feet higher, has a last frost 53 days later (March 29), a first frost 25 days earlier (November 13), a season 81 days shorter.
When it snows in San Manuel, Arizona
Measurable snow is rare here: only 9 of 20 winters from 1991 to 2020 recorded 0.1 inch or more at San Manuel, AZ, 1.6 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 85631
| When | What to do |
|---|---|
| November 26 – December 10 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| December 10 – December 24 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| January 7 – January 21 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| February 4 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by September 15 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by November 24 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| December 8 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 85631 is 2 miles from San Manuel, AZ, which stands at 3,420 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 85631 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.