USDA Hardiness Zone 9a
Frost Dates for 78218 — San Antonio, Texas
NOAA 1991–2020 normals from San Antonio Incarnate Word, TX (700 ft), 4 miles west.
Updated
In San Antonio, the last spring frost (32°F) is around February 25 in half of years and has passed by March 19 in nine years out of ten. The first fall frost comes around November 28, as early as November 7 one year in ten, leaving a typical freeze-free season of 277 days (NOAA, San Antonio Incarnate Word, TX).
- Last spring frost
- February 25
- First fall frost
- November 28
- Growing season
- 277 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
- 21%
- Snow per year
- 0.1"
median, 1991–2020
median, 1991–2020
4 of 19 observed
NOAA normal
Frost risk by date in San Antonio
Half of springs at San Antonio Incarnate Word, TX see their last 32°F night by February 25; only one in ten is past it by January 28, and one in ten still has one after March 19. Planting tender crops after March 5 leaves a 30% risk of a frost on them, after March 10 20%, and after March 19 10%. The 22 days between the even-odds date and the one-in-ten date is wider than at 63% 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 November 28 in half of years, as early as November 7 one year in ten, and holds off past December 21 one year in ten. A hard freeze of 28°F follows 17 days later, around December 15; in spring the one-in-ten date for 28°F is March 5, 14 days before the 32°F one. The freeze-free season lasts 277 days in a typical year, longer than at 76% of the 339 Texas stations; it reaches 313 days one year in ten and falls short of 249 one year in ten. On average 22 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 13 days longer, to about March 10, and return around November 16. Nights of 24°F, cold enough to damage hardier plants, come in 65% of winters and 16°F in 3%.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Feb 18 | Feb 25 | Mar 2 | Mar 6 | Mar 10 | Mar 15 | Mar 20 | Mar 27 | Apr 2 |
| 32°F | Jan 28 | Feb 5 | Feb 14 | Feb 20 | Feb 25 | Mar 1 | Mar 5 | Mar 10 | Mar 19 |
| 28°F95% of yrs | Dec 31 | Jan 14 | Jan 23 | Jan 31 | Feb 5 | Feb 12 | Feb 20 | Feb 27 | Mar 5 |
| 24°F65% of yrs | Dec 18 | Dec 31 | Jan 7 | Jan 14 | Jan 22 | Jan 30 | Feb 5 | Feb 13 | Feb 25 |
| 20°F24% of yrs | too rare for a date | ||||||||
| 16°F3% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 30 | Nov 4 | Nov 8 | Nov 12 | Nov 16 | Nov 20 | Nov 24 | Nov 29 | Dec 3 |
| 32°F | Nov 7 | Nov 14 | Nov 18 | Nov 24 | Nov 28 | Dec 1 | Dec 5 | Dec 11 | Dec 21 |
| 28°F95% of yrs | Nov 19 | Nov 28 | Dec 4 | Dec 8 | Dec 15 | Dec 22 | Jan 1 | Jan 6 | Jan 20 |
| 24°F65% of yrs | Dec 3 | Dec 11 | Dec 20 | Dec 28 | Jan 1 | Jan 5 | Jan 12 | Jan 22 | Feb 4 |
| 20°F24% of yrs | too rare for a date | ||||||||
| 16°F3% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at San Antonio Incarnate Word, 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 78218 →Compare San Antonio with another place →
Weather by month in San Antonio
August is the warmest month at San Antonio Incarnate Word, TX, averaging 95°F by day and 74°F at night; January is the coldest at 63°F and 40°F. A freezing night is all but certain in January (a 90% chance or more). From April to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 71% of years and March still brings one in 40% of years.
Warmth for growing adds up to 7,164 growing degree days a year (base 50°F), more than at 72% of the 351 Texas stations. 43% of them (3,047) have built up by the end of June, and August adds the most, 1,076. Precipitation totals 34.0 inches a year, most in May (4.4") and least in February (1.9"); May to September bring 49% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 63 | 40 | 2.2 | 91% | 7 | 135 |
| Feb | 68 | 44 | 1.9 | 71% | 4 | 201 |
| Mar | 74 | 51 | 2.4 | 40% | 1 | 396 |
| Apr | 80 | 57 | 2.3 | 1% | 0 | 563 |
| May | 86 | 66 | 4.4 | 0% | 0 | 797 |
| Jun | 92 | 72 | 3.6 | 0% | 0 | 955 |
| Jul | 94 | 74 | 2.4 | 0% | 0 | 1056 |
| Aug | 95 | 74 | 2.4 | 0% | 0 | 1076 |
| Sep | 90 | 69 | 3.9 | 0% | 0 | 875 |
| Oct | 82 | 59 | 3.9 | 3% | <1 | 634 |
| Nov | 71 | 49 | 2.5 | 54% | 2 | 326 |
| Dec | 64 | 41 | 2.1 | 88% | 8 | 152 |
Monthly normals 1991–2020 at San Antonio Incarnate Word, TX (700 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 International Airport, TX, 6 miles northwest of San Antonio, has a last frost 1 day later (February 26), the same first-frost date.
When it snows in San Antonio, Texas
Measurable snow is rare here: only 4 of 19 winters from 1991 to 2020 recorded 0.1 inch or more at San Antonio Incarnate Word, TX, 4.4 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 78218
| When | What to do |
|---|---|
| December 17 – December 31 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| December 31 – January 14 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| January 28 – February 11 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| February 25 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by September 5 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by November 14 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| November 28 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 78218 is 4 miles from San Antonio Incarnate Word, TX, which stands at 700 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 11 other ZIP codes share the station; its figures are presented in full for 78207 (San Antonio). The 2023 USDA Plant Hardiness Zone Map lists ZIP 78218 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.