Frost dates · USDA zone 6a
Frost dates for Denver, CO
Denver, CO sees its last 32 °F night of spring around May 4 and its first of fall around October 8 — a 156-day freeze-free season in a typical year.
Pick a sauce; the Plan Builder runs this station's dates and hands back the calendar, plant count and gear list.
Freeze odds, by date
| Odds | Last spring freeze after | First fall freeze before |
|---|---|---|
| 9 years in 10 | Apr 20 | Oct 20 |
| Median — 1 year in 2 | May 4 | Oct 8 |
| 1 year in 10 | May 16 | Sep 25 |
The top row is the risky edge: in 9 years of 10 a spring freeze still comes after it, so tender transplants set out then need cover. The bottom row is the cautious date — only 1 year in 10 freezes after it — and the one to plan uncovered tender transplants against. Freeze-free season: 156 days median, at least 138 in 9 years of 10, at least 175 days in 1 year of 10. NOAA ranks season length year by year, so it is not the gap between two rows above. A hard freeze (28 °F) has a median last date of Apr 22 and first of Oct 18.
Denver planting calendar, 2027
Every row runs from the median last frost (May 4) and median first frost (Oct 8) above, using each cultivar's days to maturity. Same engine as the Plan Builder.
| Crop | Start indoors | Transplant / plant | First harvest | Days |
|---|---|---|---|---|
| Hardneck GarlicSiberian (porcelain hardneck) | — | Oct 15prior fall | Jun 12 | 240 from sow |
| Spanish OnionYellow Sweet Spanish (long-day) | Feb 9 | Apr 6 | Jul 25 | 110 from transplant |
| Mustard greensGarnet Giant (Brassica juncea) | Direct sow | May 4 | Jun 3 | 30 from sow |
| CilantroSlow Bolt (Coriandrum sativum) | Apr 20 | Apr 20 | Jun 4 | 45 from sow |
| Genovese BasilGenovese | Apr 6 | May 18 | Jul 17 | 60 from transplant |
| CayenneLong Slim Cayenne (Capsicum annuum) | Mar 9 | May 11 | Jul 25 | 75 from transplant |
| HabaneroOrange Habanero (Capsicum chinense) | Feb 23 | May 18 | Aug 21 | 95 from transplant |
| JalapeñoEarly Jalapeño (Capsicum annuum) | Mar 9 | May 11 | Jul 25 | 75 from transplant |
| Marconi Red PepperMarconi Red (Capsicum annuum) | Mar 9 | May 11 | Jul 30 | 80 from transplant |
| SerranoSerrano Tampiqueño (Capsicum annuum) | Mar 9 | May 11 | Jul 30 | 80 from transplant |
| Nantes CarrotScarlet Nantes | Apr 20 | Apr 20 | Jun 29 | 70 from sow |
| TomatilloToma Verde | Mar 23 | May 11 | Jul 20 | 70 from transplant |
| Roma TomatoRoma VF (determinate paste) | Mar 23 | May 11 | Jul 25 | 75 from transplant |
| San Marzano TomatoSan Marzano (indeterminate paste) | Mar 23 | May 11 | Jul 30 | 80 from transplant |
Tight means first harvest lands within two weeks of the median first fall frost: start that crop indoors on time or cover it in fall.
What sauce can Denver grow?
Each sauce, scheduled for a Denver container garden: when the first seeds go in and when enough fruit has ripened for one batch.
Denver frost questions
When is the last frost in Denver, CO?
The median last 32 °F freeze at DENVER-STAPLETON, CO is May 4: half of years see a later one. One year in ten, a freeze still comes after May 16; nine years in ten, it comes after April 20. Source: NOAA NCEI 1991–2020 U.S. Climate Normals.
When is the first frost in Denver, CO?
The median first 32 °F freeze of fall is October 8. One year in ten it arrives before September 25; nine years in ten, before October 20.
How long is the growing season in Denver, CO?
156 days between the last spring and first fall 32 °F freeze in a median year. Nine years in ten the season runs at least 138 days; one year in ten, at least 175 days.
What growing zone is Denver, CO?
USDA hardiness zone 6a, per the 2023 USDA Plant Hardiness Zone Map for ZIP 80238. A zone describes the coldest winter night, not when frost ends, so it is the wrong number for a planting calendar — the frost dates on this page are the right one.
When should I plant tomatoes in Denver, CO?
Start Roma VF (determinate paste) seeds indoors around Mar 23 and transplant around May 11, 1 week after the median last frost. To cut the freeze risk to one year in ten, wait for May 16. First ripe fruit lands around Jul 25.
When should I plant peppers in Denver, CO?
Sow jalapeño indoors on a heat mat around Mar 9; transplant no earlier than May 11, and wait past it until nights hold above 50 °F — that can run weeks later. First green pods around Jul 25.
Nearby in Colorado
- Auroralast frost May 5
- Commerce Citylast frost May 3
- Thorntonlast frost May 2
- Centenniallast frost May 5
- Westminsterlast frost May 2
- Lakewoodlast frost May 3
All Colorado frost dates → · How frost-date math drives a sowing calendar →