Rio Grande City, TX 78585 Frost Dates
78585, near Rio Grande City, TX: the frost window
Typically, the last spring freeze lands around 01/31, roughly 156 days out. Fall's first freeze usually shows up around 12/17, roughly 321 days after the last spring frost.
Zone 9b (25 to 30°F average annual minimum) comes from the USDA Plant Hardiness Zone Map; the frost dates above are the 1991-2020 normal at the nearest reporting NOAA station for Rio Grande City, not a forecast for this year.
Stretching the season past the first frost
Rio Grande City's growing season runs out in roughly 16 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
The actual range around Rio Grande City's last frost
01/31 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 03/04 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 12/29 and only about 1 year in 10 sees frost after that.
Rio Grande City against the rest of the dataset
Rio Grande City's growing season runs about 321 days, ranking 3,294 of 40,283 US ZIP codes measured here, longest to shortest. Within TX, it ranks 209 of 2,558.
Learn more
Two guides worth reading on 78585: zone vs. frost date, on why Zone 9b and Rio Grande City's frost date answer different questions, and the frost range, on how to read the range around Rio Grande City's dates instead of trusting one.