USDA Hardiness Zone 9a
Frost Dates for 78250 — San Antonio, Texas
NOAA 1991–2020 normals from San Antonio/Seaworld, TX (940 ft), 5 miles southwest.
Updated
In San Antonio, the last spring frost (32°F) is around February 18 in half of years and has passed by March 16 in nine years out of ten. The first fall frost comes around December 9, as early as November 17 one year in ten, leaving a typical freeze-free season of 296 days (NOAA, San Antonio/Seaworld, TX).
- Last spring frost
- February 18
- First fall frost
- December 9
- Growing season
- 296 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 San Antonio
Half of springs at San Antonio/Seaworld, TX see their last 32°F night by February 18; only one in ten is past it by January 18, and one in ten still has one after March 16. Planting tender crops after February 28 leaves a 30% risk of a frost on them, after March 6 20%, and after March 16 10%. The 26 days between the even-odds date and the one-in-ten date is wider than at 84% of the 339 Texas 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 17 one year in ten, and holds off past January 13 one year in ten. A hard freeze of 28°F follows 20 days later, around December 29; in spring the one-in-ten date for 28°F is March 3, 13 days before the 32°F one. The freeze-free season lasts 296 days in a typical year, longer than at 85% of the 339 Texas stations; it reaches 334 days one year in ten and falls short of 260 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 14 days longer, to about March 4, and return around November 25. A 24°F night is unusual: 38% of winters had one.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Feb 11 | Feb 19 | Feb 24 | Feb 28 | Mar 4 | Mar 9 | Mar 14 | Mar 21 | Mar 31 |
| 32°F99% of yrs | Jan 18 | Jan 29 | Feb 5 | Feb 12 | Feb 18 | Feb 23 | Feb 28 | Mar 6 | Mar 16 |
| 28°F79% of yrs | Dec 17 | Jan 2 | Jan 14 | Jan 24 | Jan 31 | Feb 6 | Feb 14 | Feb 22 | Mar 3 |
| 24°F38% of yrs | too rare for a date | ||||||||
| 20°F8% of yrs | too rare for a date | ||||||||
| 16°F0% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Nov 5 | Nov 12 | Nov 16 | Nov 21 | Nov 25 | Nov 29 | Dec 3 | Dec 8 | Dec 15 |
| 32°F99% of yrs | Nov 17 | Nov 24 | Nov 29 | Dec 4 | Dec 9 | Dec 15 | Dec 24 | Jan 2 | Jan 13 |
| 28°F79% of yrs | Nov 28 | Dec 5 | Dec 12 | Dec 19 | Dec 29 | Jan 4 | Jan 10 | Jan 22 | Feb 9 |
| 24°F38% of yrs | too rare for a date | ||||||||
| 20°F8% of yrs | too rare for a date | ||||||||
| 16°F0% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at San Antonio/Seaworld, TX, 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 78250 →Compare San Antonio with another place →
Weather by month in San Antonio
August is the warmest month at San Antonio/Seaworld, TX, averaging 99°F by day and 74°F at night; January is the coldest at 65°F and 43°F. From April to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 64% of years and March still brings one in 28% of years.
Warmth for growing adds up to 7,892 growing degree days a year (base 50°F), more than at 87% of the 351 Texas stations. 43% of them (3,402) have built up by the end of June, and August adds the most, 1,130. Precipitation totals 31.5 inches a year, most in May (4.0") and least in February (1.8"); May to September bring 49% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 65 | 43 | 2.0 | 78% | 4 | 174 |
| Feb | 70 | 46 | 1.8 | 64% | 3 | 249 |
| Mar | 76 | 53 | 2.3 | 28% | 2 | 454 |
| Apr | 83 | 60 | 2.4 | 2% | <1 | 643 |
| May | 89 | 67 | 4.0 | 0% | 0 | 871 |
| Jun | 95 | 73 | 3.4 | 0% | 0 | 1011 |
| Jul | 97 | 74 | 2.4 | 0% | 0 | 1108 |
| Aug | 99 | 74 | 2.5 | 0% | 0 | 1130 |
| Sep | 93 | 70 | 3.1 | 0% | 0 | 943 |
| Oct | 85 | 62 | 3.8 | 0% | 0 | 717 |
| Nov | 74 | 51 | 1.9 | 32% | 1 | 392 |
| Dec | 66 | 44 | 1.9 | 65% | 4 | 200 |
Monthly normals 1991–2020 at San Antonio/Seaworld, TX (940 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, San Antonio Kelly AFB, TX, 10 miles southeast of San Antonio and 258 feet lower, has a last frost 4 days later (February 22), a first frost 7 days earlier (December 2), a season 12 days shorter.
When it snows in San Antonio, Texas
Measurable snow is rare here: only 0 of 20 winters from 1991 to 2020 recorded 0.1 inch or more at San Antonio/Seaworld, TX, 4.6 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 78250
| When | What to do |
|---|---|
| December 10 – December 24 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| December 24 – January 7 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| January 21 – February 4 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| February 18 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 78250 is 5 miles from San Antonio/Seaworld, TX, which stands at 940 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 8 other ZIP codes share the station; its figures are presented in full for 78245 (San Antonio). The 2023 USDA Plant Hardiness Zone Map lists ZIP 78250 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.