Castle Rock, CO 80109 Frost Dates
Frost dates for Castle Rock, CO, ZIP 80109
The last spring frost here typically falls around 05/09, about 254 days from today. The first fall frost typically arrives around 10/02, about 143 frost-free days later.
The USDA Plant Hardiness Zone Map puts Castle Rock in Zone 5b (-15 to -10°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
What to do before the first frost
Zone 5b around Castle Rock has about 5 weeks left before the first fall frost — that's the usual window to get a cold frame up if you want to keep harvesting past it.
Why 05/09 isn't a guarantee
05/09 is the middle of 30 years of NOAA records, not a promise. Plant by 04/30 and you're betting against frost in roughly 9 years out of 10. 05/24 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Castle Rock compares
About 143 days separate Castle Rock's last and first frost, putting it 36,484 of 40,283 ZIP codes nationally. Within CO, it ranks 378 of 624.
Learn more
the frost range explains how to read the range around Castle Rock's dates instead of trusting one, and local microclimates explains what one yard in Castle Rock can differ from the 80109 normal.