New Castle, CO 81647 Frost Dates
81647, near New Castle, CO: the frost window
The last spring frost here typically falls around 05/23, about 268 days from today. Fall's first freeze usually shows up around 09/25, roughly 124 days after the last spring frost.
New Castle sits in USDA Zone 6a (-10 to -5°F average annual minimum). The dates above are NOAA's 1991-2020 normal at the nearest reporting station, a 30-year average, not a forecast.
Stretching the season past the first frost
New Castle'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.
Why 05/23 isn't a guarantee
05/23 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/09 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 06/06 and only about 1 year in 10 sees frost after that.
New Castle against the rest of the dataset
New Castle's growing season runs about 124 days, ranking 38,833 of 40,283 US ZIP codes measured here, longest to shortest. Within CO, it ranks 455 of 624.
Learn more
Two guides worth reading on 81647: local microclimates, on what one yard in New Castle can differ from the 81647 normal, and zone vs. frost date, on why Zone 6a and New Castle's frost date answer different questions.