Morrison, CO 80421 Frost Dates
Frost dates for Morrison, CO, ZIP 80421
Typically, the last spring freeze lands around 06/16, roughly 292 days out. The first fall frost typically arrives around 09/08, about 84 frost-free days later.
The USDA Plant Hardiness Zone Map puts Morrison 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 Morrison has about 2 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.
How much risk comes with planting early here
06/16 is the middle of 30 years of NOAA records, not a promise. Plant by 06/02 and you're betting against frost in roughly 9 years out of 10. 07/01 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Morrison compares
Morrison's growing season runs about 84 days, ranking 40,006 of 40,283 US ZIP codes measured here, longest to shortest. Within CO, it ranks 561 of 624.
Learn more
local microclimates explains what one yard in Morrison can differ from the 80421 normal, and zone vs. frost date explains why Zone 5b and Morrison's frost date answer different questions.