Mount Vernon, TX 75478 Frost Dates
75478, near Mount Vernon, TX: the frost window
Around 03/15 is the usual last spring frost, about 199 days away. Fall's first freeze usually shows up around 11/14, roughly 245 days after the last spring frost.
Zone 8b (15 to 20°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 Mount Vernon, not a forecast for this year.
Stretching the season past the first frost
Mount Vernon's growing season runs out in roughly 11 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
Why 03/15 isn't a guarantee
03/15 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 02/25 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 04/04 and only about 1 year in 10 sees frost after that.
Mount Vernon against the rest of the dataset
Mount Vernon's growing season runs about 245 days, ranking 8,028 of 40,283 US ZIP codes measured here, longest to shortest. Within TX, it ranks 1,812 of 2,558.
Learn more
Two guides worth reading on 75478: zone vs. frost date, on why Zone 8b and Mount Vernon's frost date answer different questions, and the frost range, on how to read the range around Mount Vernon's dates instead of trusting one.