USDA Hardiness Zone 5b
Frost Dates for 80528 — Fort Collins, Colorado
NOAA 1991–2020 normals from Fort Collins 4 E, CO (4,920 ft), 5 miles north.
Updated
In Fort Collins, the last spring frost (32°F) is around May 3 in half of years and has passed by May 15 in nine years out of ten. The first fall frost comes around October 6, as early as September 22 one year in ten, leaving a typical freeze-free season of 154 days (NOAA, Fort Collins 4 E, CO).
- Last spring frost
- May 3
- First fall frost
- October 6
- Growing season
- 154 days
- Hardiness zone
- 5b
50% probability
50% probability
freeze-free, 50%
-15 to -10°F (-26.1 to -23.3°C) coldest night
- First snow
- October 25
- Last snow
- April 26
- Winters with snow
- 100%
- Snow per year
- 48.4"
median, 1991–2020
median, 1991–2020
30 of 30 observed
NOAA normal
Frost risk by date in Fort Collins
Half of springs at Fort Collins 4 E, CO see their last 32°F night by May 3; only one in ten is past it by April 21, and one in ten still has one after May 15. Planting tender crops after May 8 leaves a 30% risk of a frost on them, after May 11 20%, and after May 15 10%. The 12 days between the even-odds date and the one-in-ten date is narrower than at 81% of the 110 Colorado stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 6 in half of years, as early as September 22 one year in ten, and holds off past October 17 one year in ten. A hard freeze of 28°F follows 8 days later, around October 14; in spring the one-in-ten date for 28°F is May 8, 7 days before the 32°F one. The freeze-free season lasts 154 days in a typical year, longer than at 68% of the 110 Colorado stations; it reaches 171 days one year in ten and falls short of 135 one year in ten. On average 166 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 11 days longer, to about May 14, and return around September 27. Severe cold of 16°F or below comes every winter, usually between November 11 and March 18.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 3 | May 7 | May 9 | May 12 | May 14 | May 16 | May 18 | May 22 | May 26 |
| 32°F | Apr 21 | Apr 26 | Apr 29 | May 1 | May 3 | May 6 | May 8 | May 11 | May 15 |
| 28°F | Apr 8 | Apr 13 | Apr 17 | Apr 20 | Apr 23 | Apr 26 | Apr 30 | May 3 | May 8 |
| 24°F | Mar 28 | Apr 1 | Apr 4 | Apr 8 | Apr 11 | Apr 15 | Apr 19 | Apr 23 | Apr 28 |
| 20°F | Mar 12 | Mar 19 | Mar 24 | Mar 28 | Mar 31 | Apr 3 | Apr 6 | Apr 11 | Apr 18 |
| 16°F | Feb 27 | Mar 5 | Mar 9 | Mar 14 | Mar 18 | Mar 21 | Mar 25 | Mar 31 | Apr 4 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 13 | Sep 18 | Sep 22 | Sep 25 | Sep 27 | Sep 29 | Oct 1 | Oct 4 | Oct 8 |
| 32°F | Sep 22 | Sep 27 | Oct 1 | Oct 3 | Oct 6 | Oct 9 | Oct 11 | Oct 14 | Oct 17 |
| 28°F | Sep 30 | Oct 5 | Oct 9 | Oct 12 | Oct 14 | Oct 17 | Oct 20 | Oct 23 | Oct 26 |
| 24°F | Oct 8 | Oct 14 | Oct 18 | Oct 21 | Oct 24 | Oct 27 | Oct 30 | Nov 2 | Nov 6 |
| 20°F | Oct 18 | Oct 23 | Oct 28 | Oct 31 | Nov 3 | Nov 5 | Nov 8 | Nov 12 | Nov 16 |
| 16°F | Oct 24 | Oct 31 | Nov 4 | Nov 7 | Nov 11 | Nov 14 | Nov 17 | Nov 21 | Nov 25 |
Freeze probabilities 1991–2020 at Fort Collins 4 E, CO, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 80528 →Compare Fort Collins with another place →
Weather by month in Fort Collins
July is the warmest month at Fort Collins 4 E, CO, averaging 88°F by day and 58°F at night; December is the coldest at 42°F and 16°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 61% of years.
Warmth for growing adds up to 2,614 growing degree days a year (base 50°F), more than at 55% of the 110 Colorado stations. 31% of them (816) have built up by the end of June, and July adds the most, 702. Precipitation totals 14.8 inches a year, most in May (2.5") and least in January (0.4"); May to September bring 58% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 43 | 15 | 0.4 | 100% | 31 | 0 |
| Feb | 45 | 18 | 0.4 | 100% | 27 | 1 |
| Mar | 55 | 26 | 1.1 | 100% | 25 | 16 |
| Apr | 61 | 34 | 2.0 | 100% | 13 | 63 |
| May | 70 | 43 | 2.5 | 61% | 2 | 235 |
| Jun | 81 | 52 | 1.8 | 0% | 0 | 502 |
| Jul | 88 | 58 | 1.6 | 0% | 0 | 702 |
| Aug | 85 | 55 | 1.3 | 0% | 0 | 628 |
| Sep | 77 | 47 | 1.4 | 30% | 1 | 367 |
| Oct | 63 | 34 | 1.2 | 100% | 11 | 92 |
| Nov | 51 | 24 | 0.7 | 100% | 26 | 9 |
| Dec | 42 | 16 | 0.4 | 100% | 31 | 0 |
Monthly normals 1991–2020 at Fort Collins 4 E, CO (4,920 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, Loveland 2N, CO, 6 miles southwest of Fort Collins and 160 feet higher, has a last frost 7 days later (May 10), a first frost 5 days earlier (October 1), a season 12 days shorter.
When it snows in Fort Collins, Colorado
The first measurable snow (0.1 inch or more) in Fort Collins usually arrives around October 25, and the last of the season around April 26. Those are the middle dates across the winters of 1991–2020 at Fort Collins 4 E, CO, 5.1 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 7 days after the last snow.
Planting calendar for 80528
| When | What to do |
|---|---|
| February 22 – March 8 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 8 – March 22 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 5 – April 19 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 3 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 14 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 22 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 6 onward | Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter. |
The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.
Where these figures come from
ZIP 80528 is 5 miles from Fort Collins 4 E, CO, which stands at 4,920 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 5 other ZIP codes share the station; its figures are presented in full for 80525 (Fort Collins). The 2023 USDA Plant Hardiness Zone Map lists ZIP 80528 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°C) over 1991–2020; a zone describes winter lows, not frost dates.
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.