Boulder, CO 80304 Frost Dates
When can you plant in Boulder, CO?
Typically, the last spring freeze lands around 05/06, roughly 251 days out. The first fall frost typically arrives around 10/05, about 151 frost-free days later.
Boulder 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.
What to do before the first frost
About 5 weeks of growing season left in Boulder before the first fall frost — a cold frame or row cover can stretch harvest weeks past that date.
The actual range around Boulder's last frost
05/06 is the middle of 30 years of NOAA records, not a promise. Plant by 04/24 and you're betting against frost in roughly 9 years out of 10. 05/18 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Boulder compares
About 151 days separate Boulder's last and first frost, putting it 34,935 of 40,283 ZIP codes nationally. Within CO, it ranks 305 of 624.
Learn more
the frost range covers how to read the range around Boulder's dates instead of trusting one. local microclimates covers what one yard in Boulder can differ from the 80304 normal.