Frost dates for Fort Collins, Colorado
In Fort Collins, half of springs have had their last frost by May 2 (and 1 spring in 10 still has one after May 14), and half of falls have had their first frost by October 7, leaving about 157 frost-free days in a typical year. Here is how sure those dates are, what they mean for planting, and where they come from.
Frost dates for
Fort Collins, Colorado
Last spring frost
May 2
Half of springs have their last frost by this date. For a safer bet, wait until May 14: only 1 spring in 10 has a frost after that.
First fall frost
October 7
Half of falls have their first frost by this date. In 1 fall in 10 it comes by September 24.
Growing season
157 days
Frost-free days in a typical year. 9 years in 10 get at least 139.
Hardiness zone
5b
2023 USDA map: the coldest night of winter averages −15°F to −10°F. It was 5b on the 2012 map too. All 5 ZIP codes within about 6 miles of the city's center are in zone 5b.
Stations near you disagree. NOAA's Fort Collins (2 miles away, at 5,000 feet above sea level), the one we used, gives a typical last frost of May 2 and a typical first frost of October 7. NOAA's Buckhorn Mountain 1 E (15 miles away, at 7,400 feet above sea level) gives a typical last frost of May 21 and a typical first frost of September 29. So the typical last frost could fall anywhere from May 2 to 21 and the typical first frost from September 29 to October 7, depending on whether your garden is more like one or the other. Local terrain matters: hillsides, valley floors, water and city heat can change frost dates a lot over a few miles. Treat the dates here as a starting point, and compare with a nearby gardener or your county extension office.
Print a year planner for Fort Collins
Frost risk through the year
How sure are these dates?
A frost date is a probability, not a promise. NOAA worked out, from 30 years of nightly lows, how often the last spring frost and the first fall frost fall on each date. The middle column is the typical year. The outer columns are the early and late years that come about once a decade.
| Early year 1 in 10 | Typical year 1 in 2 | Late year 1 in 10 | |
|---|---|---|---|
| Last frost in spring | April 18 | May 2 | May 14 |
| First frost in fall | September 24 | October 7 | October 20 |
The frost-free season between them runs 157 days in a typical year. In 1 year in 10 it is 175 days or longer, and in 1 year in 10 it is 139 days or shorter.
- Hard freeze (28°F): typically last on April 20 and first on October 17. It is a harder freeze than the 32°F frost line, cold enough to damage many garden plants; how hardy a crop is decides whether it comes through. (The National Weather Service's own hard-freeze threshold varies from office to office.)
- Frost possible (36°F at the station): typically last on May 12 and first on September 29. On clear, still nights the ground can be several degrees colder than the thermometer, so frost can form on plants when the official reading is in the mid-30s.
In 8 springs out of 10, the last frost in Fort Collins comes between April 18 and May 14, a window of 26 days. That is narrower than at most NOAA stations (the typical window is 31 days), so the typical date is a steadier guide here than in most places.
Among Colorado's 210 NOAA stations with a frost every year, 80 percent have their typical last frost later than Fort Collins does.
Planting calendar for Fort Collins
These dates count from the typical last and first frosts, using the planting rules published by Colorado State University Extension (spring), Virginia Cooperative Extension (fall crops) and University of Minnesota Extension (garlic, where winters are hard). Weather in any one year can run early or late, so check the forecast before you plant tender crops.
Your season is too short for a separate fall planting of cabbage: sown late enough to be a fall crop, it wouldn't be ready before the typical first frost. Your spring planting is your harvest.
| When | What to do | Why then |
|---|---|---|
| February | ||
| February 14 to March 14 | Broccoli and cabbage Start seeds indoors | 5 to 7 weeks before planting them out |
| February 28 to March 28 | Cauliflower Start seeds indoors | 5 to 7 weeks before planting out |
| March | ||
| March 14 to April 4 | Eggplant Start seeds indoors | 6 to 9 weeks before planting out |
| March 21 to April 4 | Peppers Start seeds indoors | 6 to 8 weeks before planting out |
| March 28 to April 11 | Tomatoes Start seeds indoors | 5 to 7 weeks before planting out |
| April | ||
| April 4 to 18 | Peas, spinach, lettuce, radishes, onion sets, turnips Sow outdoors, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April 4 to 18 | Broccoli and cabbage Plant out, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April 18 to May 2 | Beets, carrots, potatoes, Swiss chard Plant outdoors, as early as | semi-hardy crops: up to 2 weeks before the typical last frost |
| April 18 to May 2 | Cauliflower Plant out, as early as | semi-hardy: up to 2 weeks before the typical last frost |
| May | ||
| May 2 | Snap beans, sweet corn, cucumbers, summer squash Sow outdoors around | tender crops: around the typical last frost date |
| May 16 | Tomatoes, peppers, eggplant Plant out from | very tender: 2 weeks or more after the typical last frost |
| May 16 | Melons, winter squash, pumpkins, lima beans Sow outdoors from | very tender: 2 weeks or more after the typical last frost |
| June | ||
| June 1 to 15 | Broccoli for fall Start seeds | set the plants out by July 20 |
| July | ||
| July 11 | Snap beans for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| July 15 | Carrots for fall Last date to sow | 70 days to harvest, plus 2 weeks for slower fall growth |
| July 16 | Cucumbers for fall Last date to sow | 55 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| July 20 | Peas for fall Last date to sow | 65 days to harvest, plus 2 weeks for slower fall growth |
| July 21 | Summer squash for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| July 25 | Leaf lettuce and beets for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth |
| August | ||
| August 4 | Turnips and kohlrabi for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth |
| August 14 | Spinach for fall Last date to sow | 40 days to harvest, plus 2 weeks for slower fall growth |
| August 24 | Radishes for fall Last date to sow | 30 days to harvest, plus 2 weeks for slower fall growth |
| September | ||
| September 24 | Tomatoes, peppers, squash, melons, cucumbers Watch the forecast from | in 1 fall in 10 the first frost comes by this date; pick tender crops before a frost |
| October | ||
| October 24 to 31 | Garlic Plant cloves | one or two weeks after the typical first hard freeze (28°F), our reading of the first killing frost |
Want more insurance? Shift every spring date 12 days later. That plans around May 14, the date after which only 1 spring in 10 has a frost.
For spring bulbs such as tulips and daffodils, plant once the soil has cooled to about 50 to 55°F and keep going until a couple of weeks before the ground freezes. Our guide to fall planting explains how to tell.
Where these numbers come from
These dates come from NOAA's weather station Fort Collins (station USC00053005), 2 miles from the center of Fort Collins. It sits at about the same elevation, 5,000 feet above sea level. NOAA rates this station's record as standard: at least 24 of the 30 years, with gaps filled from nearby stations.
Our ZIP code lookup matches these 3 ZIP codes to the same station, so they get the same dates: 80521, 80524, 80535. Hardiness zones are worked out separately for each ZIP code.
Nearby places
- Greeley, Colorado: last frost around May 2, first frost around October 8 (20 miles away)
- Cheyenne, Wyoming: last frost around May 12, first frost around October 1 (40 miles away)
- Westminster, Colorado: last frost around May 2, first frost around October 11 (45 miles away)
See frost dates across Colorado, or look up your own ZIP code for the station nearest you. Want the background? Read what a last frost date really means.