Basalt, CO 81621 Frost Dates
81621, near Basalt, CO: the frost window
The last spring frost here typically falls around 05/31, about 276 days from today. Fall's first freeze usually shows up around 09/23, roughly 114 days after the last spring frost.
Zone 6a (-10 to -5°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 Basalt, not a forecast for this year.
Stretching the season past the first frost
Basalt's growing season runs out in roughly 4 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 Basalt's last frost
05/31 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/16 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 06/14 and only about 1 year in 10 sees frost after that.
Basalt against the rest of the dataset
Basalt's growing season runs about 114 days, ranking 39,354 of 40,283 US ZIP codes measured here, longest to shortest. Within CO, it ranks 490 of 624.
Learn more
Two guides worth reading on 81621: zone vs. frost date, on why Zone 6a and Basalt's frost date answer different questions, and the frost range, on how to read the range around Basalt's dates instead of trusting one.