Frost dates & planting calendar for Denver, CO
Frost dates
May 4
Last spring frost, typical
In half of the years that freeze, the last frost comes later.
Safer date: May 16. Only 1 freeze year in 10 has a frost after this.
Oct 8
First fall frost, typical
In half of the years that freeze, it comes earlier.
Early date: Sep 25. Only 1 freeze year in 10 freezes before this.
156
Days, typical frost-free season
From NOAA’s 1991–2020 climate normals for this station.
6a
USDA hardiness zone
Coldest night of the winter, averaged over 1991–2020: −10 to −5°F (−23.3 to −20.6°C).
Zone for ZIP 80238, the ZIP nearest the city center; zones can vary within a city. What zone 6a means.
What to plant right now
As of Nov 9, 2026
Typical frost-free season: 156 days. Station: Denver-Stapleton, CO, 1 km away. Source: NOAA NCEI U.S. Climate Normals 1991–2020 (32°F threshold).
Hardiness zones: 2023 USDA Plant Hardiness Zone Map, PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed 9 Nov 2026.
Can I plant tomatoes now?
Not this season. Start tomato seeds indoors from Mar 21 to Apr 4, then plant them out from May 16 to May 30.
Planting calendar
Windows are counted from the safer dates (May 16 in spring, Sep 25 in fall). Going by the typical dates instead gains you about 2 weeks in spring, with more risk.
March
The next window opens in March.
Peppertender
Next: start indoors from Mar 7
- Start indoors
- Mar 7 – Mar 21
- Transplant outdoors
- May 16 – May 30
Parsleyhalf hardy
Next: start indoors from Mar 7
- Start indoors
- Mar 7 – Mar 21
- Sow outdoors
- May 2 – May 16
Tomatotender
Next: start indoors from Mar 21
- Start indoors
- Mar 21 – Apr 4
- Transplant outdoors
- May 16 – May 30
Eggplanttender
Next: start indoors from Mar 21
- Start indoors
- Mar 21 – Apr 4
- Transplant outdoors
- May 16 – May 30
Broccolihardy
Next: start indoors from Mar 21
- Start indoors
- Mar 21 – Apr 4
- Transplant outdoors
- Apr 18 – May 16
- Sow outdoors
- Apr 18 – May 2
- Sow for fall
- Jul 3 – Jul 17
Cabbagehardy
Next: start indoors from Mar 21
- Start indoors
- Mar 21 – Apr 4
- Transplant outdoors
- Apr 18 – May 16
- Sow outdoors
- Apr 18 – May 2
- Sow for fall
- Jul 3 – Jul 17
Cauliflowerhalf hardy
Next: start indoors from Mar 21
- Start indoors
- Mar 21 – Apr 4
- Transplant outdoors
- May 2 – May 16
- Sow outdoors
- Apr 25 – May 16
- Sow for fall
- Jul 3 – Jul 17
Brussels sproutshardy
Next: start indoors from Mar 21
- Start indoors
- Mar 21 – Apr 4
- Sow outdoors
- Apr 25 – Apr 25
- Sow for fall
- Jul 3 – Jul 17
Marigoldtender
Next: start indoors from Mar 21
- Start indoors
- Mar 21 – Mar 21
- Transplant outdoors
- May 16 – May 16
Calendulahalf hardy
Next: start indoors from Mar 21
- Start indoors
- Mar 21 – Apr 4
- Sow outdoors
- May 9 – May 16
Mexican sunflowertender
Next: start indoors from Mar 21
- Start indoors
- Mar 21 – Apr 4
- Sow outdoors
- May 16 – May 16
April
The next window opens in April.
Leaf lettucehardy
Next: sow outdoors from Apr 4
- Transplant outdoors
- Apr 18 – May 2
- Sow outdoors
- Apr 4 – May 2
Head lettucehardy
Next: sow outdoors from Apr 4
- Transplant outdoors
- Apr 18 – May 2
- Sow outdoors
- Apr 4 – May 2
Zinniatender
Next: start indoors from Apr 4
- Start indoors
- Apr 4 – Apr 18
- Sow outdoors
- May 16 – May 16
Nasturtiumtender
Next: start indoors from Apr 4
- Start indoors
- Apr 4 – Apr 18
- Sow outdoors
- May 16 – May 16
Sunflowertender
Next: start indoors from Apr 4
- Start indoors
- Apr 4 – Apr 18
Cucumbertender
Next: start indoors from Apr 18
- Start indoors
- Apr 18 – May 2
- Sow outdoors
- May 16 – May 23
Summer squashtender
Next: start indoors from Apr 18
- Start indoors
- Apr 18 – May 2
- Sow outdoors
- May 16 – May 23
Winter squashtender
Next: start indoors from Apr 18
- Start indoors
- Apr 18 – May 2
- Sow outdoors
- May 23 – May 30
Watermelontender
Next: start indoors from Apr 18
- Start indoors
- Apr 18 – May 2
- Transplant outdoors
- May 23 – May 30
- Sow outdoors
- May 23 – May 30
Cantaloupetender
Next: start indoors from Apr 18
- Start indoors
- Apr 18 – Apr 25
- Sow outdoors
- May 23 – May 30
Peahardy
Next: sow outdoors from Apr 18
- Sow outdoors
- Apr 18 – May 2
Spinachhardy
Next: sow outdoors from Apr 18
- Sow outdoors
- Apr 18 – May 2
Kohlrabihardy
Next: sow outdoors from Apr 18
- Sow outdoors
- Apr 18 – May 2
- Sow for fall
- Jul 3 – Jul 17
Radishhardy
Next: sow outdoors from Apr 18
- Sow outdoors
- Apr 18 – May 2
Beethalf hardy
Next: sow outdoors from Apr 18
- Sow outdoors
- Apr 18 – May 16
Turniphardy
Next: sow outdoors from Apr 18
- Sow outdoors
- Apr 18 – May 2
Bulb onionhardy
Next: sow outdoors from Apr 18
- Sow outdoors
- Apr 18 – May 2
Green onionhardy
Next: sow outdoors from Apr 18
- Sow outdoors
- Apr 18 – May 2
Kalehardy
Next: sow outdoors from Apr 25
- Sow outdoors
- Apr 25 – Apr 25
- Sow for fall
- Jul 3 – Jul 17
Collardshardy
Next: sow outdoors from Apr 25
- Sow outdoors
- Apr 25 – Apr 25
- Sow for fall
- Jul 3 – Jul 17
May
The next window opens in May.
Swiss chardhalf hardy
Next: sow outdoors from May 2
- Sow outdoors
- May 2 – May 16
Carrothalf hardy
Next: sow outdoors from May 2
- Sow outdoors
- May 2 – May 16
Potatohalf hardy
Next: sow outdoors from May 2
- Sow outdoors
- May 2 – May 16
Parsniphalf hardy
Next: sow outdoors from May 2
- Sow outdoors
- May 2 – May 16
Dillhalf hardy
Next: sow outdoors from May 2
- Sow outdoors
- May 2 – May 9
Bush beantender
Next: sow outdoors from May 16
- Sow outdoors
- May 16 – May 16
Pole beantender
Next: sow outdoors from May 16
- Sow outdoors
- May 16 – May 16
Sweet corntender
Next: sow outdoors from May 16
- Sow outdoors
- May 16 – May 16
Basiltender
Next: sow outdoors from May 16
- Sow outdoors
- May 16 – May 16
Marjoramtender
Next: transplant outdoors from May 16
- Transplant outdoors
- May 16 – May 16
Pumpkintender
Next: sow outdoors from May 23
- Sow outdoors
- May 23 – May 30
Lima beantender
Next: sow outdoors from May 30
- Sow outdoors
- May 30 – May 30
August
The next window opens in August.
Sweet alyssumhardy
Next: sow for fall from Aug 14
- Sow for fall
- Aug 14 – Aug 14
No window listed
No frost-based window for these crops.
Mustard greenshalf hardy
No frost-based window listed.
No frost-based sowing window is listed for mustard greens.
Crop guidance from university extension services; see each crop page for sources.
Questions
- When is the last frost in Denver?
- The typical last spring frost (32°F) in Denver is May 4. In 1 out of 10 years that freeze, a frost still comes after May 16.
- When is the first frost in Denver?
- The typical first fall frost is Oct 8. In 1 out of 10 years that freeze, it arrives before Sep 25.
- When should I start tomato seeds in Denver?
- Start tomato seeds indoors between Mar 21 and Apr 4, counting back from the safer last-frost date.
- What planting zone is Denver in?
- Denver is in USDA hardiness zone 6a on the 2023 map, going by ZIP 80238, the ZIP nearest the city center. Zones can vary within a city. The zone describes how cold winter nights get, not when to plant; for that, use the frost dates on this page.
Nearby cities
- Colorado Springs, CO 100 km
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