Frost dates for Denver, Colorado
In Denver, half of springs have had their last frost by May 4 (and 1 spring in 10 still has one after May 16), and half of falls have had their first frost by October 8, leaving about 156 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
Denver, Colorado
Last spring frost
May 4
Half of springs have their last frost by this date. For a safer bet, wait until May 16: only 1 spring in 10 has a frost after that.
First fall frost
October 8
Half of falls have their first frost by this date. In 1 fall in 10 it comes by September 25.
Growing season
156 days
Frost-free days in a typical year. 9 years in 10 get at least 138.
Hardiness zone
6a
2023 USDA map: the coldest night of winter averages −10°F to −5°F. It was 6a on the 2012 map too. All 21 ZIP codes within about 6 miles of the city's center are in zone 6a.
Print a year planner for Denver
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 20 | May 4 | May 16 |
| First frost in fall | September 25 | October 8 | October 20 |
The frost-free season between them runs 156 days in a typical year. In 1 year in 10 it is 175 days or longer, and in 1 year in 10 it is 138 days or shorter.
- Hard freeze (28°F): typically last on April 22 and first on October 18. 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 October 1. 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 Denver comes between April 20 and May 16, 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, 71 percent have their typical last frost later than Denver does.
Planting calendar for Denver
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 16 to March 16 | Broccoli and cabbage Start seeds indoors | 5 to 7 weeks before planting them out |
| March | ||
| March 2 to 30 | Cauliflower Start seeds indoors | 5 to 7 weeks before planting out |
| March 16 to April 6 | Eggplant Start seeds indoors | 6 to 9 weeks before planting out |
| March 23 to April 6 | Peppers Start seeds indoors | 6 to 8 weeks before planting out |
| March 30 to April 13 | Tomatoes Start seeds indoors | 5 to 7 weeks before planting out |
| April | ||
| April 6 to 20 | Peas, spinach, lettuce, radishes, onion sets, turnips Sow outdoors, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April 6 to 20 | Broccoli and cabbage Plant out, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April 20 to May 4 | Beets, carrots, potatoes, Swiss chard Plant outdoors, as early as | semi-hardy crops: up to 2 weeks before the typical last frost |
| April 20 to May 4 | Cauliflower Plant out, as early as | semi-hardy: up to 2 weeks before the typical last frost |
| May | ||
| May 4 | Snap beans, sweet corn, cucumbers, summer squash Sow outdoors around | tender crops: around the typical last frost date |
| May 18 | Tomatoes, peppers, eggplant Plant out from | very tender: 2 weeks or more after the typical last frost |
| May 18 | Melons, winter squash, pumpkins, lima beans Sow outdoors from | very tender: 2 weeks or more after the typical last frost |
| June | ||
| June 2 to 16 | Broccoli for fall Start seeds | set the plants out by July 21 |
| July | ||
| July 12 | 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 16 | Carrots for fall Last date to sow | 70 days to harvest, plus 2 weeks for slower fall growth |
| July 17 | 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 21 | Peas for fall Last date to sow | 65 days to harvest, plus 2 weeks for slower fall growth |
| July 22 | 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 26 | Leaf lettuce and beets for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth |
| August | ||
| August 5 | Turnips and kohlrabi for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth |
| August 15 | Spinach for fall Last date to sow | 40 days to harvest, plus 2 weeks for slower fall growth |
| August 25 | Radishes for fall Last date to sow | 30 days to harvest, plus 2 weeks for slower fall growth |
| September | ||
| September 25 | 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 25 to November 1 | 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 16, 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 Denver-Stapleton (station USW00023062), less than a mile from the center of Denver. It sits at about the same elevation, 5,290 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.
The same station also gives the frost dates for Thornton, Commerce City, Littleton and Englewood.
Our ZIP code lookup matches these 15 ZIP codes to the same station, so they get the same dates: 80010, 80011, 80022, 80024, 80045, 80206, 80207, 80220, 80224, 80229, 80230, 80238, 80239, 80246, 80266. Hardiness zones are worked out separately for each ZIP code.
Nearby places
- Aurora, Colorado: last frost around May 5, first frost around October 9 (10 miles away)
- Centennial, Colorado: last frost around May 5, first frost around October 8 (10 miles away)
- Westminster, Colorado: last frost around May 2, first frost around October 11 (15 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.