Median last frost from Apr 27 to Jun 15 across Colorado
NOAA stations
200
Median last frost, Denver
Apr 30
Passed in 9 of 10 years
May 13
Last frost
Last spring frost dates in Colorado
Grand Junction and Denver both reach a median last frost around the end of April, but Durango waits until about Jun 1 and Twin Lakes near Leadville, above 9,200 feet, until about Jun 16.
Three dates per station from the NOAA 1991 to 2020 normals. The median is the date half of springs run past. The last column is the date the last 32°F night has passed by in 9 years out of 10, the one to hold tender transplants for.
Station
Elevation
Early (1 in 10 years later than this)
Median last frost
Passed in 9 of 10 years
Median first fall frost
Grand JunctionGrand Junction Walker Field, USW00023066
4,858 ft
Apr 11
Apr 28
May 14
Oct 16
DenverDenver Water Dept, USC00052223
5,228 ft
Apr 15
Apr 30
May 13
Oct 12
Lamar Municipal AirportLamar Municipal Airport, USW00003013
3,704 ft
Apr 19
May 2
May 17
Oct 7
Durango La Plata County AirportDurango La Plata County Airport, USW00093005
6,660 ft
May 17
Jun 1
Jun 15
Sep 27
Twin Lakes, near LeadvilleTwin Lakes Reservoir, USC00058501
9,236 ft
Jun 3
Jun 16
Jun 29
Sep 10
Crop chart
When to start seeds in Colorado, spring 2027
Counted back from the median last frost at Denver, April 30. Pick another station to redraw the chart for it.
Start indoorsHarden offSet outSow outdoorsMedian last frostLast freeze passed in 9 of 10 years
Every crop, counted from a median last frost of April 30
Crop
Start indoors
Set out
Sow outdoors
Frost class
Tomato
Mar 12 to Mar 26
May 7 to May 14
Tender, very tender
Pepper
Mar 5 to Mar 19
May 14 to May 21
Tender, very tender
Eggplant
Mar 5 to Mar 19
May 14 to May 21
Tender, very tender
Basil
Mar 19 to Apr 2
May 14 to May 21
Tender
Celery
Feb 5 to Feb 19
Apr 30 to May 7
Tender
Cucumber
Apr 9 to Apr 16
May 7 to May 14
Apr 30 to May 7
Tender
Summer squash
Apr 16 to Apr 23
May 14 to May 21
Apr 30 to May 7
Tender
Winter squash
Apr 16 to Apr 23
May 14 to May 21
May 14 to May 21
Tender, very tender
Pumpkin
Apr 16 to Apr 23
May 14 to May 21
May 14 to May 21
Tender, very tender
Melon (cantaloupe)
Apr 16 to Apr 23
May 14 to May 21
Tender, very tender
Watermelon
Apr 9 to Apr 23
May 14 to May 21
Tender, very tender
Onion (from seed)
Jan 22 to Feb 5
Apr 2 to Apr 9
Hardy
Leek
Jan 22 to Feb 5
Apr 2 to Apr 9
Hardy
Parsley
Jan 29 to Feb 5
Apr 9 to Apr 16
Half-hardy
Broccoli
Feb 19 to Mar 5
Apr 2 to Apr 16
Hardy
Brussels sprouts
Feb 19 to Mar 5
Apr 2 to Apr 16
Hardy
Cabbage
Feb 19 to Mar 5
Apr 2 to Apr 9
Hardy
Cauliflower
Mar 5 to Mar 19
Apr 16 to Apr 23
Half-hardy
Kale
Feb 19 to Mar 5
Apr 2 to Apr 9
Hardy
Lettuce
Feb 26 to Mar 5
Apr 2 to Apr 9
Hardy
Swiss chard
Mar 5 to Mar 19
Apr 16 to Apr 23
Apr 2 to Apr 9
Half-hardy
Spinach
Feb 5 to Feb 19
Mar 19 to Apr 9
Apr 2 to Apr 16
Hardy
Peas
Apr 2 to Apr 16
Hardy
Radish
Apr 2 to Apr 16
Hardy
Carrot
Apr 16 to Apr 30
Half-hardy
Beet
Apr 16 to Apr 30
Half-hardy
Beans
Apr 30 to May 7
Tender
Sweet corn
Apr 30 to May 7
Tender
Tomato seedlings at the seed leaf stage, one to a pot. The University of Minnesota Extension holds off on fertilizer until a seedling has several sets of true leaves, then feeds at quarter strength once a week.“Tomato Seedlings (49768696597)” by Amanda Slater from Coventry, West Midlands, UK, CC BY-SA 2.0
Extension guide
What Colorado State University Extension advises
Colorado State University Extension publishes the planting guide Colorado gardeners work from, Vegetable Planting Guide (CMG GardenNotes #720).
“As early as 2-4 weeks before the date of the average last spring frost.”
Setting out a tomato in June at a community garden. Tender crops go out after the last frost, and after a week or two of hardening off outdoors. “Volunteer planting heirloom tomato (4704185147)”, Pacific Southwest Region 5, Public domain
Seed starting questions for Colorado
Count back from the median last frost where you garden. At Denver (Denver Water Dept) that date is April 30, so for spring 2027 onions start indoors Jan 22 to Feb 5, peppers Mar 5 to Mar 19 and tomatoes Mar 12 to Mar 26. Across Colorado's 200 NOAA stations the median last frost runs from Apr 27 to Jun 15 for the middle 90 percent, so a garden near Cochetopa Creek starts later than one near Palisade.
It depends on the station. The earliest median last spring freeze in Colorado is April 17 at Palisade; the latest is June 21 at Cochetopa Creek. A median is a coin flip: at Denver the last 32°F freeze comes after April 30 in half of years, and has passed by May 13 in 9 of 10 years (NOAA 1991 to 2020 normals).
UNH Extension sets tomatoes out 1 to 2 weeks after the last frost, which at Denver is May 7 to May 14 in 2027. Tomatoes are frost tender, so the date to watch is May 13, when 9 of 10 springs at Denver have had their last 32°F night. Hardening off starts two weeks before setting out (Apr 23 to May 7).
Colorado State University Extension's Vegetable Planting Guide puts it this way: "As early as 2-4 weeks before the date of the average last spring frost." The guide is linked below with the date it was read (September 21, 2026).
UNH Extension gives 8 to 10 weeks from seed to transplant for both, and sets peppers out 2 weeks after the last frost and eggplant 2 to 3 weeks after, so the sowing date is 6 to 8 weeks before the median last frost. At Denver that is Mar 5 to Mar 19 for peppers.
About two weeks. University of Missouri Extension: "Hardening should be started about two weeks before planting in the garden." University of Minnesota Extension adds that seedlings should go out on a cloudy day or in the late afternoon.
Grand Junction and Denver both reach a median last frost around the end of April, but Durango waits until about Jun 1 and Twin Lakes near Leadville, above 9,200 feet, until about Jun 16. Each station carries its own dates: Grand Junction Apr 28 and Twin Lakes, near Leadville Jun 16 at the median.
