Fort Collins, Colorado Frost Dates, Growing Season & Hardiness Zone
Frost odds and planting zone for Fort Collins for the 2027 season, based on 1991–2020 normals.
Last frost date
May 2
typical (50% chance of a later 32°F night)
Safer date: May 14 (10% risk)
earlyMay 2
typicalMay 14
safer
First fall frost
Oct 7
typical (50% chance it has happened by then)
Early-risk date: Sep 24 (10%)
Growing season
157 days
typical frost-free (32°F) season
Short year: 139 days (1 year in 10 is shorter)
USDA hardiness zone
5b
2023 map: -15 to -10°F average coldest night
2012 map: 5b
Where you live in the metro matters. The typical last frost ranges from May 2 at Fort Collins to May 13 at Nunn 7 NNE.
Typical last freeze (32°F): May 2. In 1 year out of 10, the last one comes after May 14.
Based on NOAA station Fort Collins (USC00053005), 2.2 mi NNW, elevation 5,004 ft (+11 ft vs. city center). Confidence: High.
When is the last frost in Fort Collins?
The typical last 32°F night is May 2, and in 1 year out of 10 a freeze still comes after May 14. Cold 36°F nights (frost possible on plants) typically last longer, to around May 12. The last hard freeze (28°F) typically comes earlier, around Apr 20.
Planting between the typical date (May 2) and the safer 1-in-10 date (May 14) is a bet. Over those 12 days, let the 10-day forecast guide you.
Cool nights hang on after the last freeze: the typical last 36°F night (frost possible on plants in low spots) is around May 12, 10 days later than the typical last 32°F night. Frost can form on leaves on clear, calm nights even with the thermometer above freezing.
Of the 6 eligible stations near Fort Collins, ours has the earliest typical last frost. In a colder pocket, plan closer to May 14.
| Threshold | 10% (safer) | 30% | 50% (typical) | 90% (early) |
|---|---|---|---|---|
| 36°F (frost possible on plants) | May 26 | May 17 | May 12 | May 1 |
| 32°F freeze | May 14 | May 7 | May 2 | Apr 18 |
| 28°F hard freeze | May 5 | Apr 27 | Apr 20 | Apr 5 |
All probabilities (10–90%)
| Threshold | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F (frost possible on plants) | May 26 | May 21 | May 17 | May 14 | May 12 | May 10 | May 7 | May 4 | May 1 |
| 32°F freeze | May 14 | May 10 | May 7 | May 4 | May 2 | Apr 30 | Apr 28 | Apr 24 | Apr 18 |
| 28°F hard freeze | May 5 | Apr 30 | Apr 27 | Apr 23 | Apr 20 | Apr 17 | Apr 13 | Apr 9 | Apr 5 |
Is it safe to plant after Mother's Day in Fort Collins?
Mother's Day is the usual planting signal for many gardeners around Fort Collins (CSU PlantTalk). In 2027 that's May 9. As of that date, NOAA 1991–2020 normals at Fort Collins give between 20% and 30% odds of another 32°F night and between 60% and 70% odds of another 36°F night (frost possible on plants).
Is it too early to plant in Fort Collins?
Before May 2 the odds of another 32°F night are better than even; after May 14 they are about 1 in 10 or less.
Today's risk is computed in your browser from the same NOAA probability table, shown as the range between the two nearest NOAA probability levels.
When is the first frost in Fort Collins?
Half of years get their first 32°F night by Oct 7. In 1 year out of 10, it arrives as early as Sep 24. The first 36°F night (frost possible on plants) typically comes around Sep 29, and the first 28°F hard freeze around Oct 17.
To time a fall crop, count back from the typical first frost (Oct 7) or the safer Sep 24. The planting calendar works it out crop by crop.
| Threshold | 10% (early) | 30% | 50% (typical) | 90% (late) |
|---|---|---|---|---|
| 36°F (frost possible on plants) | Sep 15 | Sep 24 | Sep 29 | Oct 11 |
| 32°F freeze | Sep 24 | Oct 2 | Oct 7 | Oct 20 |
| 28°F hard freeze | Oct 2 | Oct 11 | Oct 17 | Oct 28 |
All probabilities (10–90%)
| Threshold | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F (frost possible on plants) | Sep 15 | Sep 21 | Sep 24 | Sep 27 | Sep 29 | Oct 1 | Oct 3 | Oct 6 | Oct 11 |
| 32°F freeze | Sep 24 | Sep 29 | Oct 2 | Oct 5 | Oct 7 | Oct 10 | Oct 13 | Oct 16 | Oct 20 |
| 28°F hard freeze | Oct 2 | Oct 7 | Oct 11 | Oct 14 | Oct 17 | Oct 19 | Oct 22 | Oct 25 | Oct 28 |
How long is Fort Collins's growing season?
A typical year in Fort Collins has 157 days between the last spring and first fall 32°F nights. In about 1 year in 10, there are fewer than 139 days.
A season this long fits most warm-season vegetables planted on time. Long-season crops do best when started from transplants.
Growing degree days measure the heat available for crops to grow. The station averages 2,746 a year (base 50°F).
| Threshold | 10% (long year) | 50% (typical) | 90% (short year) |
|---|---|---|---|
| 36°F (frost possible on plants) | 154 days | 138 days | 120 days |
| 32°F freeze | 175 days | 157 days | 139 days |
| 28°F hard freeze | 198 days | 179 days | 159 days |
How does Fort Collins's season compare?
Of the 20 Colorado cities with frost dates on this site, Fort Collins has a typical frost-free season of 157 days, which is the 10th longest.
Compared with the 56 U.S. cities with frost dates on this site, this typical frost-free season is longer than in 10 and shorter than in 45.
Growing degree days (base 50°F)
Annual normal: 2,746 GDD (NOAA flag S, 29 years). Running total by the end of each month (sum of NOAA daily GDD normals, so the year-end total can differ slightly from the annual normal):
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 0 | 3 | 28 | 107 | 365 | 884 | 1,597 | 2,240 | 2,628 | 2,733 | 2,746 | 2,746 |
What growing zone is Fort Collins? (USDA 2023)
On the 2023 USDA map, Fort Collins is zone 5b (-15 to -10°F average coldest winter night). That's no change from the 2012 map.
| ZIP | 2023 | 2012 | Change | Share of ZIP in Fort Collins |
|---|---|---|---|---|
| 80512 | 5b | 5b | unchanged | 0% |
| 80521 | 5b | 5b | unchanged | 40% |
| 80524 | 5b | 5b | unchanged | 10% |
| 80525 mostly in city | 5b | 5b | unchanged | 71% |
| 80526 | 5b | 5b | unchanged | 46% |
| 80528 | 5b | 5b | unchanged | 37% |
| 80547 | 5b | 5b | unchanged | 1% |
Other ZIPs touching Fort Collins and PO-box ZIPs
ZIPs outside the 805 prefix that overlap the city boundary:
- none
PO-box and single-address 805xx ZIPs have no Census area, so we cannot tell which city they serve: 80501 (5b/5b), 80502 (5b/5b), 80503 (6a/5b), 80504 (5b/5b), 80510 (5b/5a), 80511 (5b/5a), 80513 (5b/5b), 80514 (5b/5b), 80515 (5b/5b), 80516 (5b/5b), 80517 (5a/5a), 80520 (5b/5b), 80522 (5b/5b), 80523 (n/a/5b), 80527 (5b/5b), 80530 (5b/5b), 80532 (5b/5a), 80533 (6a/5b), 80534 (5b/5b), 80535 (5b/5b), 80536 (5b/5a), 80537 (5b/5b), 80538 (5b/5b), 80539 (5b/5b), 80540 (5b/5b), 80541 (5b/5b), 80542 (5b/5b), 80543 (5b/5b), 80544 (n/a/5b), 80545 (5a/5a), 80546 (5b/5b), 80549 (5b/5b), 80550 (5b/5b), 80551 (5b/5b), 80553 (5b/5b) (2023/2012).
Zones: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed 2026-10-08. Shown as published in the ZIP tables; this page does not show a zone map. Not the official USDA Plant Hardiness Zone Map (official map: planthardiness.ars.usda.gov).
Does the new zone change Fort Collins's frost dates?
No. A hardiness zone reflects only the average coldest winter temperature, not the timing of spring or fall frost. Fort Collins's frost dates come from NOAA's 1991–2020 frost probabilities, and the 2023 zone map didn't change them. Pick perennials that survive winter by zone; time your planting by frost dates.
Why do Fort Collins frost dates differ between websites?
You may see May 7 given as Fort Collins's last frost date. That's the 30%-risk date, meaning about 3 years in 10 still have a 32°F night after it. Our headline date is May 2, the 50% (median) date.
The 'safer' date, May 14, is the 10%-risk date. A 32°F night after it happens in only about 1 year in 10.
May 12 is the 50% date for a 36°F night (frost possible on plants), not a 32°F freeze. Sites that treat 36°F as the danger line show later dates.
The choice of weather station matters too. The 6 stations within 25 miles of the city center that pass our quality rules give typical (50%) last 32°F frost dates from May 2 to May 13; see the table below.
| Date | What it is (NOAA 1991–2020) |
|---|---|
| May 7 | 32°F last frost, 30% risk (a 'balanced' date) |
| May 12 | 36°F last cold night, 50% (frost possible on plants) |
| May 14 | 32°F last frost, 10% risk (the 'safer' date) |
| Apr 20 | 28°F last hard freeze, 50% |
| May 3 | 32°F last frost, 50%, at Fort Collins 4 E (nearest station with NOAA flag S) |
| Station | Distance | Elevation | Typical last frost |
|---|---|---|---|
| Fort Collins used here | 2.2 mi NNW | 5,004 ft | May 2 |
| Greeley UNC | 21.7 mi ESE | 4,715 ft | May 2 |
| Fort Collins 4 E | 2.9 mi NE | 4,920 ft | May 3 |
| Loveland 2 N | 7.9 mi S | 5,080 ft | May 10 |
| Waterdale | 11.4 mi SW | 5,230 ft | May 12 |
| Nunn 7 NNE | 24.1 mi NE | 5,390 ft | May 13 |
Which weather station is this based on?
- Station
- Fort Collins (NOAA USC00053005, COOP)
- Distance
- 2.2 mi NNW of the city center
- Elevation
- 5,004 ft; city center 4,993 ft (USGS), difference +11 ft
- Record
- NOAA completeness flag S, 29 of 30 years (1991–2020)
- Confidence
- High (rule)
Confidence: High. At 2.2 miles from the city center and only 11 ft off in elevation, with frost statistics that meet our completeness rule (NOAA flag S, 29 of 30 years), this station is a close match.
| Station | ID | Distance | Elev. (Δ) | Last frost 50% | First frost 50% | Season 50% | NOAA flag / years |
|---|---|---|---|---|---|---|---|
| Fort Collins | USC00053005 | 2.2 mi NNW | 5,004 ft (+11) | May 2 | Oct 7 | 157 d | S / 29 |
| Fort Collins 4 E | USC00053006 | 2.9 mi NE | 4,920 ft (-73) | May 3 | Oct 6 | 154 d | S / 29 |
| Loveland 2 N | USC00055236 | 7.9 mi S | 5,080 ft (+87) | May 10 | Oct 1 | 142 d | S / 25 |
| Waterdale | USC00058839 | 11.4 mi SW | 5,230 ft (+237) | May 12 | Oct 1 | 141 d | R / 23 |
| Greeley UNC | USC00053553 | 21.7 mi ESE | 4,715 ft (-278) | May 2 | Oct 8 | 159 d | S / 25 |
| Nunn 7 NNE | USW00094074 | 24.1 mi NE | 5,390 ft (+397) | May 13 | Sep 27 | 136 d | R / 17 |
Other stations within 25 mi (not used)
- Buckhorn Mountain 1 E (USC00051060), 13.0 mi WNW, 7,400 ft: typical last frost May 21. Not used: |elev diff| 2407 ft > 500 ft.
74 other NOAA normals stations within 40 km (mostly rain gauges) have no frost statistics.
Fort Collins planting dates at a glance
Balanced dates use the 30%-risk last-frost date as the anchor. The Fort Collins planting calendar has typical and safe dates, fall planting and a month-by-month list for 27 vegetables.
| Crop | Start indoors | Plant outdoors (balanced) | Fall |
|---|---|---|---|
| Tomatoes | Apr 25 – May 9 | Jun 13 | – |
| Peppers | Mar 26 – Apr 9 | May 21 | – |
| Potatoes | – | Apr 23 – May 7 | – |
| Onions (dry, from sets) | – | Apr 9–23 | – |
| Peas | – | Apr 9–23 | sow by Jul 20 |
| Lettuce (leaf) | – | Apr 9–23 | sow by Jul 25 |
| Carrots | – | Apr 23 – May 7 | sow by Jul 15 |
| Beans (snap) | – | May 7 | sow by Jul 11 |
| Summer squash | – | May 7 | sow by Jul 21 |
| Broccoli | Feb 19 – Mar 5 | Apr 9–23 | transplant by Jul 20 |
| Cabbage | Feb 19 – Mar 5 | Apr 9–23 | transplant by Jun 30 |
| Cauliflower | Mar 5–19 | Apr 23 – May 7 | – |
| Kohlrabi | – | Apr 9–23 | sow by Aug 4 |
| Green onions | – | Apr 9–23 | sow by Jul 25 |
| Radishes | – | Apr 9–23 | sow by Aug 24 |
| Spinach | – | Apr 9–23 | sow by Aug 14 |
| Turnips | – | Apr 9–23 | sow by Aug 4 |
| Beets | – | Apr 23 – May 7 | sow by Jul 25 |
| Swiss chard | – | Apr 23 – May 7 | sow by Jul 25 |
| Parsnips | – | Apr 23 – May 7 | – |
| Sweet corn | – | May 7 | – |
| Cucumbers | – | May 7 | sow by Jul 16 |
| Eggplant | Mar 19 – Apr 9 | May 21 | – |
| Cantaloupe | – | May 21 | – |
| Watermelon | – | May 21 | – |
| Winter squash | – | May 21 | – |
| Garlic | – | – | plant Oct 1–14 |
When to plant tomatoes in Fort Collins · Fall planting dates for Fort Collins
Frost dates near Fort Collins
| City | Distance | Last frost | First frost | Season | Zone 2023 |
|---|---|---|---|---|---|
| Loveland frost dates | 9 mi | May 10 | Oct 1 | 142 days | 5b |
| Greeley frost dates | 18 mi | May 2 | Oct 8 | 159 days | 5a–5b |
| Longmont frost dates | 26 mi | May 7 | Oct 5 | 151 days | 5b–6a |
| Boulder frost dates | 38 mi | May 6 | Oct 5 | 151 days | 6a |
| Thornton frost dates | 44 mi | May 2 | Oct 11 | 160 days | 6a |
| Commerce City frost dates | 48 mi | May 3 | Oct 7 | 155 days | 5b |
Frequently asked questions
What is the average last frost date in Fort Collins?
The typical (median, 50%) last 32°F night in Fort Collins is May 2, based on NOAA 1991–2020 normals at Fort Collins. For a safer target, use May 14; after that, only about 1 year in 10 still has a freeze.
When is the first frost in Fort Collins?
The first 32°F night typically arrives by Oct 7. About 1 year in 10, it comes as early as Sep 24. A 36°F night (frost possible on plants) typically shows up around Sep 29.
What growing zone is Fort Collins, Colorado?
Zone 5b. That's Fort Collins's USDA hardiness zone on both the 2023 map and the older 2012 map.
Is it too early to plant in Fort Collins?
For frost-tender plants, yes if it's before May 2: until then, the odds of another 32°F night are better than even. Between May 2 and May 14, the risk falls from 50% to 10%. Cool-season crops like peas and lettuce can go in weeks earlier; see the planting calendar.
What temperature is a killing frost?
For tender crops like tomatoes, a light frost is a killing frost. CSU Extension calls 28–32°F a light frost and below 28°F a heavy frost. Our NOAA odds cover three thresholds: 36°F (frost possible on plants), 32°F (freeze, our headline) and 28°F (hard freeze).
Is first frost the same as first freeze?
Not quite. A freeze is when the air reaches 32°F. Frost is ice that forms on surfaces, and on calm, clear nights it can form with the air a few degrees above freezing. So in Fort Collins, the first 36°F night (frost possible on plants) typically comes around Sep 29, before the first 32°F night (Oct 7).
Download & sources
- Add Fort Collins frost & planting dates to your calendar (.ics, 2027)
- Printable planting calendar (PDF)
- How these numbers are calculated
Data: NOAA NCEI U.S. Climate Normals 1991–2020 (annual/seasonal and daily normals, station USC00053005); USDA Plant Hardiness Zone ZIP tables 2023 and 2012 by the PRISM Group, Oregon State University; Census 2020 ZIP/place relationship file; USGS elevation. Long-term odds, not a forecast. Figures and sentences are generated from these data by fixed rules; see the methodology. Last updated 2026-10-08.