Denver frost dates and planting season

Name: Denver
Address: Colorado, United States

When to plant vegetables here. Cover calendars (fleece, cold frame, unheated greenhouse) are on each plant’s when-to-plant page.

Denver has a short growing season, with roughly 139 frost-free days between the typical frost dates. Typical last spring frost: around April 21 (half of years later). Typical first fall frost: around September 8. Plant cool-season crops after about May 4; wait until about June 1 for warm-season crops.

Frost-free days139Apr 21 – Sep 8

Frost-free season in Denver. Based on average frost dates. Adjust a week or two for your conditions.

Cover calendars (fleece, cold frame, unheated greenhouse) live on each crop’s when-to-plant page.

Weekly possible temperature−25 – 97 °F

Frost-free days139

Typical last spring frostApril 21

Typical first fall frostSeptember 8

Days suitable for warm-season vegetables112 (June 1 – September 20)

Days suitable for cool-season vegetables77 (May 4 – June 7; September 7 – October 18)

Calculated by Plan & Plant · Method · Data 2019–2026

Frost and suitability dates are typical figures from climate statistics. Microclimates vary; they are not a guarantee.

Frost dates calculated by Plan & Plant from Weather data by Open-Meteo.com (CC BY 4.0). Local frost pockets, valleys and coastal sites can differ by 1–3 weeks.

How we calculated this

Data: ERA5-Land via Open-Meteo, cell 39.70, -105.00, years 2019–2026 (not a 30-year climate normal yet).
Typical and safer dates: Typical last frost is the date after which half of winters in this sample had no more frost; safer is later in the sample so fewer winters still frosted.
Confidence: Provisional — short or thin sample for this place.
Full methodology (algorithm 2026-10-season-6).

Report a problem

What to plant when

Cool-season vegetables

Earliest outdoor start: May 4

Suitable window: May 4 – June 7; September 7 – October 18

Cool-season crops prefer cooler weather.

Midsummer is often too hot, so suitable weeks split into more than one window.

See cool-season details

Warm-season vegetables

Earliest outdoor start: June 1

Suitable window: June 1 – September 20

Warm-season crops need mild or warm weather and cannot take frost.

Frost kills these crops, and cold snaps set them back.

See warm-season details

Green = usually good weeks to grow; blue or gray = usually too cold for that crop type.

Starter plants for Denver

Cool-season

Radish Sow: March 18 – June 9 Planting dates
Arugula Sow: March 18 – June 9 Planting dates
Spinach Sow: March 10 – June 9 Planting dates
Lettuce Sow: March 10 – June 9 Planting dates
Kale Sow: March 18 – May 12 Planting dates
Beet Sow: March 24 – June 10 Planting dates

Warm-season

Green bean Sow: May 17 – June 1 Planting dates
Tomato Transplant: June 1 – June 18 Start indoors, then transplant. Planting dates
Bell pepper Transplant: June 12 – June 13 Start indoors, then transplant. Planting dates

How these dates are judged

Last frost: The typical last spring date when frost is still expected.
First frost: The typical first fall date when frost returns.
Frost-free days: The approximate days between those two dates.
Cool-season vegetables: Crops that prefer cooler weather, such as lettuce, kale, peas, and radish.
Warm-season vegetables: Crops that need warm weather and cannot take frost, such as tomato, pepper, squash, and beans.

Cool-season planting window

May 4 – Jun 7; Sep 7 – Oct 18 (77 days)

Warm-season planting window

Jun 1 – Sep 20 (112 days)

Usually too cold

January 1 – May 3
October 19 – December 31

Weekly temperatures and planting windows

Temperatures across the year for Denver, with cool- and warm-season weeks and frost dates.

Possible min to max
Average min to max
Suitable
Tolerable
Too cold
Too hot

Selected week · tap a week or use the arrows

Week 19 · May 4 – May 10

Average 40 to 65 °F · Possible 31 to 83 °F

Cool season: tolerable

Warm season: too cold

A week is suitable for a crop type when its average low and high sit inside that type's range and its possible readings stay within the frost and heat limits (cool: 28 °F to 81 °F, warm: 32 °F to 90 °F); crossing a limit makes it tolerable, and for warm crops any chance of frost makes it too cold.

Based on average frost dates.

Colorado, United States · 39.7, -105 · 2026

Coldest weekly possible temperature−25 °F

Hottest weekly possible temperature97 °F

Last expected spring frostApril 21

First expected fall frostSeptember 8

Show all 53 weeks