USDA Hardiness Zone 9b
Frost Dates for 78582 — Rio Grande City, Texas
NOAA 1991–2020 normals from Rio Grande City, TX (172 ft), 9 miles southwest.
Updated
In Rio Grande City, the last spring frost (32°F) is around January 31 in half of years and has passed by March 4 in nine years out of ten. The first fall frost comes around December 17, as early as November 22 one year in ten, leaving a typical freeze-free season of 321 days (NOAA, Rio Grande City, TX).
- Last spring frost
- January 31
- First fall frost
- December 17
- Growing season
- 321 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
- 5%
- Snow per year
- 0.1"
median, 1991–2020
median, 1991–2020
1 of 20 observed
NOAA normal
Frost risk by date in Rio Grande City
Half of springs at Rio Grande City, TX see their last 32°F night by January 31; only one in ten is past it by December 29, and one in ten still has one after March 4. Planting tender crops after February 15 leaves a 30% risk of a frost on them, after February 25 20%, and after March 4 10%. The 32 days between the even-odds date and the one-in-ten date is wider than at 94% 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 17 in half of years, as early as November 22 one year in ten, and holds off past January 20 one year in ten. A hard freeze of 28°F follows 12 days later, around December 29; in spring the one-in-ten date for 28°F is February 20, 12 days before the 32°F one. The freeze-free season lasts 321 days in a typical year, longer than at 92% of the 339 Texas stations; it reaches 358 days one year in ten and falls short of 283 one year in ten. On average 6 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 22 days longer, to about February 22, and return around December 1. A 24°F night is unusual: 23% of winters had one.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jan 22 | Feb 1 | Feb 8 | Feb 15 | Feb 22 | Feb 27 | Mar 2 | Mar 7 | Mar 14 |
| 32°F93% of yrs | Dec 29 | Jan 8 | Jan 17 | Jan 24 | Jan 31 | Feb 6 | Feb 15 | Feb 25 | Mar 4 |
| 28°F60% of yrs | Dec 13 | Dec 25 | Dec 31 | Jan 6 | Jan 12 | Jan 19 | Jan 26 | Feb 5 | Feb 20 |
| 24°F23% of yrs | too rare for a date | ||||||||
| 20°F4% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Nov 11 | Nov 17 | Nov 22 | Nov 27 | Dec 1 | Dec 4 | Dec 9 | Dec 18 | Dec 28 |
| 32°F93% of yrs | Nov 22 | Nov 30 | Dec 4 | Dec 10 | Dec 17 | Dec 24 | Jan 1 | Jan 8 | Jan 20 |
| 28°F60% of yrs | Dec 2 | Dec 8 | Dec 17 | Dec 24 | Dec 29 | Jan 1 | Jan 7 | Jan 17 | Feb 1 |
| 24°F23% of yrs | too rare for a date | ||||||||
| 20°F4% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Rio Grande City, 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 78582 →Compare Rio Grande City with another place →
Weather by month in Rio Grande City
August is the warmest month at Rio Grande City, TX, averaging 99°F by day and 75°F at night; January is the coldest at 71°F and 45°F. From April to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 35% of years and March still brings one in 15% of years.
Warmth for growing adds up to 8,984 growing degree days a year (base 50°F), more than at 96% of the 351 Texas stations. 46% of them (4,094) have built up by the end of June, and August adds the most, 1,155. Precipitation totals 22.6 inches a year, most in September (5.1") and least in January (0.8"); May to September bring 62% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 71 | 45 | 0.8 | 65% | 2 | 277 |
| Feb | 76 | 50 | 1.0 | 35% | 1 | 377 |
| Mar | 82 | 56 | 1.3 | 15% | <1 | 597 |
| Apr | 89 | 63 | 1.0 | 0% | 0 | 770 |
| May | 94 | 70 | 2.9 | 0% | 0 | 987 |
| Jun | 98 | 74 | 2.8 | 0% | 0 | 1087 |
| Jul | 99 | 75 | 2.0 | 0% | 0 | 1149 |
| Aug | 99 | 75 | 1.3 | 0% | 0 | 1155 |
| Sep | 94 | 71 | 5.1 | 0% | 0 | 974 |
| Oct | 88 | 63 | 2.5 | 1% | 0 | 803 |
| Nov | 79 | 54 | 1.1 | 19% | <1 | 501 |
| Dec | 72 | 47 | 0.8 | 56% | 2 | 309 |
Monthly normals 1991–2020 at Rio Grande City, TX (172 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, La Joya, TX, 24 miles east of Rio Grande City, has a last frost 8 days earlier (January 23), a first frost 11 days later (December 28), a season 19 days longer.
When it snows in Rio Grande City, Texas
Measurable snow is rare here: only 1 of 20 winters from 1991 to 2020 recorded 0.1 inch or more at Rio Grande City, TX, 8.7 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 78582
| When | What to do |
|---|---|
| November 22 – December 6 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| December 6 – December 20 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| January 3 – January 17 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| January 31 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by September 24 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by December 3 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| December 17 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 78582 is 9 miles from Rio Grande City, TX, which stands at 172 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 78582 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.