USDA Hardiness Zone 9b
Frost Dates for 85140 — San Tan Valley, Arizona
NOAA 1991–2020 normals from Chandler Heights, AZ (1,425 ft), 7 miles west.
Updated
In San Tan Valley, the last spring frost (32°F) is around February 1 in half of years and has passed by February 27 in nine years out of ten. The first fall frost comes around December 11, as early as November 23 one year in ten, leaving a typical freeze-free season of 315 days (NOAA, Chandler Heights, AZ).
- Last spring frost
- February 1
- First fall frost
- December 11
- Growing season
- 315 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
- —
median, 1991–2020
median, 1991–2020
0 of 15 observed
NOAA normal
Frost risk by date in San Tan Valley
Half of springs at Chandler Heights, AZ see their last 32°F night by February 1; only one in ten is past it by January 2, and one in ten still has one after February 27. Planting tender crops after February 12 leaves a 30% risk of a frost on them, after February 18 20%, and after February 27 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 11 in half of years, as early as November 23 one year in ten, and holds off past January 1 one year in ten. A hard freeze of 28°F follows 15 days later, around December 26; in spring the one-in-ten date for 28°F is February 11, 16 days before the 32°F one. The freeze-free season lasts 315 days in a typical year, longer than at 80% of the 98 Arizona stations; it reaches 347 days one year in ten and falls short of 281 one year in ten. On average 11 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 20 days longer, to about February 21, and return around November 28. A 24°F night is unusual: 12% of winters had one.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jan 29 | Feb 5 | Feb 11 | Feb 16 | Feb 21 | Feb 26 | Mar 2 | Mar 6 | Mar 11 |
| 32°F99% of yrs | Jan 2 | Jan 8 | Jan 17 | Jan 24 | Feb 1 | Feb 5 | Feb 12 | Feb 18 | Feb 27 |
| 28°F70% of yrs | Dec 15 | Dec 24 | Dec 31 | Jan 3 | Jan 8 | Jan 15 | Jan 24 | Feb 2 | Feb 11 |
| 24°F12% of yrs | too rare for a date | ||||||||
| 20°F0% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Nov 12 | Nov 18 | Nov 22 | Nov 25 | Nov 28 | Dec 1 | Dec 5 | Dec 9 | Dec 14 |
| 32°F99% of yrs | Nov 23 | Nov 29 | Dec 3 | Dec 7 | Dec 11 | Dec 15 | Dec 19 | Dec 25 | Jan 1 |
| 28°F70% of yrs | Dec 4 | Dec 11 | Dec 16 | Dec 21 | Dec 26 | Dec 30 | Jan 2 | Jan 12 | Jan 29 |
| 24°F12% of yrs | too rare for a date | ||||||||
| 20°F0% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Chandler Heights, 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 85140 →Compare San Tan Valley with another place →
Weather by month in San Tan Valley
July is the warmest month at Chandler Heights, AZ, averaging 104°F by day and 79°F at night; December is the coldest at 64°F and 39°F. From March to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 46% of years.
Warmth for growing adds up to 7,921 growing degree days a year (base 50°F), more than at 75% of the 102 Arizona stations. 41% of them (3,234) have built up by the end of June, and July adds the most, 1,282.
| Month | High °F | Low °F | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|
| Jan | 66 | 41 | 81% | 3 | 128 |
| Feb | 70 | 43 | 46% | 1 | 185 |
| Mar | 77 | 48 | 8% | <1 | 384 |
| Apr | 85 | 53 | 0% | 0 | 570 |
| May | 93 | 62 | 0% | 0 | 859 |
| Jun | 103 | 71 | 0% | 0 | 1109 |
| Jul | 104 | 79 | 0% | 0 | 1282 |
| Aug | 103 | 78 | 0% | 0 | 1243 |
| Sep | 98 | 72 | 0% | 0 | 1042 |
| Oct | 87 | 59 | 0% | 0 | 705 |
| Nov | 74 | 47 | 21% | 1 | 319 |
| Dec | 64 | 39 | 86% | 5 | 96 |
Monthly normals 1991–2020 at Chandler Heights, AZ (1,425 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, Casa Grande Nm, AZ, 12 miles south of San Tan Valley, has a last frost 16 days later (February 17), a first frost 12 days earlier (November 29), a season 31 days shorter.
When it snows in San Tan Valley, Arizona
Measurable snow is rare here: only 0 of 15 winters from 1991 to 2020 recorded 0.1 inch or more at Chandler Heights, AZ, 6.9 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 85140
| When | What to do |
|---|---|
| November 23 – December 7 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| December 7 – December 21 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| January 4 – January 18 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| February 1 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by September 18 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by November 27 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| December 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 85140 is 7 miles from Chandler Heights, AZ, which stands at 1,425 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 9 other ZIP codes share the station; its figures are presented in full for 85142 (Queen Creek). The 2023 USDA Plant Hardiness Zone Map lists ZIP 85140 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.