Longmont, CO 80501 Frost Dates
When can you plant in Longmont, CO?
The last spring frost here typically falls around 05/06, about 251 days from today. The first fall frost typically arrives around 10/05, about 151 frost-free days later.
Zone 5b (-15 to -10°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 Longmont, not a forecast for this year.
What to do before the first frost
About 5 weeks of growing season left in Longmont before the first fall frost — a cold frame or row cover can stretch harvest weeks past that date.
The actual range around Longmont'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 Longmont compares
Longmont's growing season runs about 151 days, ranking 34,937 of 40,283 US ZIP codes measured here, longest to shortest. Within CO, it ranks 307 of 624.
Learn more
zone vs. frost date covers why Zone 5b and Longmont's frost date answer different questions. the frost range covers how to read the range around Longmont's dates instead of trusting one.