USDA Hardiness Zone 9b
Frost Dates for 85121 — ZIP 85121
NOAA 1991–2020 normals from Casa Grande, AZ (1,400 ft), 7 miles south.
Updated
In ZIP 85121, the last spring frost (32°F) is around February 5 in half of years and has passed by February 28 in nine years out of ten. The first fall frost comes around December 6, as early as November 18 one year in ten, leaving a typical freeze-free season of 305 days (NOAA, Casa Grande, AZ).
- Last spring frost
- February 5
- First fall frost
- December 6
- Growing season
- 305 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
- 0"
median, 1991–2020
median, 1991–2020
0 of 18 observed
NOAA normal
Frost risk by date in ZIP 85121
Half of springs at Casa Grande, AZ see their last 32°F night by February 5; only one in ten is past it by January 5, and one in ten still has one after February 28. Planting tender crops after February 17 leaves a 30% risk of a frost on them, after February 23 20%, and after February 28 10%. The 23 days between the even-odds date and the one-in-ten date measure how much the end of the frost season moves from year to year, so a fixed calendar date is a gamble here.
In fall the first 32°F night comes by December 6 in half of years, as early as November 18 one year in ten, and holds off past December 29 one year in ten. A hard freeze of 28°F follows 16 days later, around December 22; in spring the one-in-ten date for 28°F is February 15, 13 days before the 32°F one. The freeze-free season lasts 305 days in a typical year; it reaches 340 days one year in ten and falls short of 273 one year in ten. On average 17 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 21 days longer, to about February 26, and return around November 24. A 24°F night is unusual: 28% of winters had one.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jan 31 | Feb 9 | Feb 16 | Feb 21 | Feb 26 | Mar 1 | Mar 4 | Mar 9 | Mar 16 |
| 32°F99% of yrs | Jan 5 | Jan 16 | Jan 26 | Jan 31 | Feb 5 | Feb 10 | Feb 17 | Feb 23 | Feb 28 |
| 28°F79% of yrs | Dec 16 | Dec 28 | Jan 1 | Jan 8 | Jan 14 | Jan 23 | Jan 31 | Feb 6 | Feb 15 |
| 24°F28% 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 7 | Nov 13 | Nov 17 | Nov 21 | Nov 24 | Nov 27 | Dec 1 | Dec 5 | Dec 11 |
| 32°F99% of yrs | Nov 18 | Nov 24 | Nov 29 | Dec 3 | Dec 6 | Dec 10 | Dec 15 | Dec 21 | Dec 29 |
| 28°F79% of yrs | Nov 29 | Dec 6 | Dec 10 | Dec 15 | Dec 22 | Dec 27 | Jan 1 | Jan 8 | Jan 24 |
| 24°F28% of yrs | too rare for a date | ||||||||
| 20°F3% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Casa Grande, 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 85121 →Compare ZIP 85121 with another place →
Weather by month in ZIP 85121
July is the warmest month at Casa Grande, AZ, averaging 107°F by day and 78°F at night; December is the coldest at 68°F and 38°F. From March to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 56% of years.
Warmth for growing adds up to 8,266 growing degree days a year (base 50°F). 41% of them (3,394) have built up by the end of June, and July adds the most, 1,316. Precipitation totals 7.9 inches a year, most in August (1.5") and least in April (0.2"); May to September bring 44% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 69 | 39 | 0.8 | 83% | 5 | 145 |
| Feb | 73 | 42 | 1.0 | 56% | 2 | 205 |
| Mar | 80 | 47 | 0.8 | 10% | <1 | 421 |
| Apr | 88 | 53 | 0.2 | 0% | 0 | 608 |
| May | 96 | 60 | 0.2 | 0% | 0 | 881 |
| Jun | 106 | 70 | 0.2 | 0% | 0 | 1135 |
| Jul | 107 | 78 | 0.9 | 0% | 0 | 1316 |
| Aug | 105 | 77 | 1.5 | 0% | 0 | 1280 |
| Sep | 100 | 71 | 0.7 | 0% | 0 | 1066 |
| Oct | 91 | 57 | 0.5 | 0% | <1 | 738 |
| Nov | 78 | 45 | 0.4 | 32% | 2 | 349 |
| Dec | 68 | 38 | 0.7 | 86% | 7 | 123 |
Monthly normals 1991–2020 at Casa Grande, AZ (1,400 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 east of ZIP 85121, has a last frost 12 days later (February 17), a first frost 7 days earlier (November 29), a season 21 days shorter.
When it snows in ZIP 85121
Measurable snow is rare here: only 0 of 18 winters from 1991 to 2020 recorded 0.1 inch or more at Casa Grande, AZ, 6.7 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 85121
| 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 13 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by November 22 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| December 6 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 85121 is 7 miles from Casa Grande, AZ, which stands at 1,400 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 85122 (Casa Grande). The 2023 USDA Plant Hardiness Zone Map lists ZIP 85121 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.