Denver, Colorado Frost Dates, Growing Season & Hardiness Zone

When is the last frost in Denver?

In half of years, the last 32°F night has passed by Apr 30. In 1 year out of 10, one still comes after May 13. The last 36°F night (frost possible on plants) typically comes later, around May 8, and the last 28°F hard freeze earlier, around Apr 18.

Planting between the typical date (Apr 30) and the safer 1-in-10 date (May 13) is a bet. Over those 13 days, let the 10-day forecast guide you.

The typical last 36°F night (frost possible on plants in low spots) comes around May 8, 8 days after the typical last 32°F night. On clear, calm nights, frost can form on leaves even when the thermometer reads above freezing.

Our station has the earliest typical last frost of the 11 eligible stations near Denver. If your yard runs cool, lean toward the safer May 13 date.

Is it safe to plant after Mother's Day in Denver?

Many Denver-area gardeners wait for Mother's Day to plant (CSU PlantTalk). In 2027, it falls on May 9. As of that date, the chance of another 32°F night is between 10% and 20%, and the chance of another 36°F night (frost possible on plants) is between 40% and 50% (NOAA 1991–2020, Denver Water Dept.).

Is it too early to plant in Denver?

Before Apr 30 the odds of another 32°F night are better than even; after May 13 they are about 1 in 10 or less.

Today's risk is computed in your browser from the same NOAA probability table, shown as the range between the two nearest NOAA probability levels.

When is the first frost in Denver?

By Oct 12, half of years have had their first 32°F night. In 1 year out of 10, it comes as early as Sep 28. In a typical year, look for the first 36°F night (frost possible on plants) around Oct 4 and the first 28°F hard freeze around Oct 21.

For fall crops, count back from Oct 12, or from Sep 28 to be safe. Our planting calendar does the math for each crop.

How long is Denver's growing season?

Denver's frost-free season (32°F) typically runs 165 days. In about 1 year out of 10, it's shorter than 145 days.

That's enough time for most warm-season vegetables if they go in on time. Long-season crops do best started from transplants.

Growing degree days measure the heat available for crops to grow. The station averages 3,396 a year (base 50°F).

How does Denver's season compare?

Of the 20 Colorado cities with frost dates on this site, Denver has a typical frost-free season of 165 days, which is the 3rd longest.

Nationwide, across the 56 cities with frost dates on this site, the typical frost-free season here outlasts the one in 17 of them and falls short of the one in 38.

Growing degree days (base 50°F)

Annual normal: 3,396 GDD (NOAA flag R, 18 years). Running total by the end of each month (sum of NOAA daily GDD normals, so the year-end total can differ slightly from the annual normal):

What growing zone is Denver? (USDA 2023)

Denver is in USDA zone 6a on the 2023 map, which means an average coldest winter night of -10 to -5°F. Most of the city was 5b on the 2012 map, and 31 of 34 city ZIPs found in both tables moved up half a zone.

Zones: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed 2026-10-08. Shown as published in the ZIP tables; this page does not show a zone map. Not the official USDA Plant Hardiness Zone Map (official map: planthardiness.ars.usda.gov).

Does the new zone change Denver's frost dates?

No. Hardiness zones are based only on the average coldest winter temperature. They say nothing about when spring and fall frosts happen. Denver's frost dates come from NOAA's 1991–2020 frost probabilities, which did not change with the 2023 zone map. Use your zone to pick perennials that will survive winter, and your frost dates to time planting.

Why do Denver frost dates differ between websites?

You may see May 4 given as Denver's last frost date. That's the 30%-risk date, meaning about 3 years in 10 still have a 32°F night after it. Our headline date is Apr 30, the 50% (median) date.

May 13 is the date we call 'safer': it's the 10%-risk date, with a 32°F night after it in only about 1 year in 10.

May 8 is the 50% date for a 36°F night (frost possible on plants), not a 32°F freeze. Sites that treat 36°F as the danger line show later dates.

Station choice is another reason dates differ. Our 11 qualifying stations within 25 miles of the city center range from Apr 30 to May 8 for the typical (50%) last 32°F frost (table below).

Which weather station is this based on?

Station

Denver Water Dept. (NOAA USC00052223, COOP)

Distance

1.2 mi SW of the city center

Elevation

5,228 ft; city center 5,238 ft (USGS), difference −10 ft

Record

NOAA completeness flag R, 22 of 30 years (1991–2020)

Confidence

High (rule)

Confidence: High. At 1.2 miles from the city center and only 10 ft off in elevation, with frost statistics that meet our completeness rule (NOAA flag R, 22 of 30 years), this station is a close match.

Note: NOAA rates this station's frost statistics 'R' (representative). That means they use 22 of the 30 years in 1991–2020, with missing months filled in from surrounding stations. For comparison, the nearest station with a full 'S' (standard) record, Denver-Stapleton (6.6 mi away), has a typical last frost of May 4.

Denver planting dates at a glance

Balanced dates use the 30%-risk last-frost date as the anchor. The Denver planting calendar has typical and safe dates, fall planting and a month-by-month list for 27 vegetables.

When to plant tomatoes in Denver · Fall planting dates for Denver

Frost dates near Denver

All Colorado cities

Frequently asked questions

What is the average last frost date in Denver?

Apr 30 is the median (50%) date for Denver's last 32°F night, from NOAA 1991–2020 normals at Denver Water Dept. To play it safe, use May 13: only about 1 year in 10 has a freeze after it.

When is the first frost in Denver?

Typically by Oct 12 for the first 32°F night, though about 1 year in 10 it comes as early as Sep 28. The first 36°F night (frost possible on plants) typically shows up around Oct 4.

What growing zone is Denver, Colorado? Is Denver zone 5 or 6?

Denver is in USDA hardiness zone 6a on the current 2023 map (zone 6 for short). On the older 2012 map, most of the city was 5b. That's why older references still say 'zone 5'.

Is it too early to plant in Denver?

For frost-tender plants, yes if it's before Apr 30: until then, the odds of another 32°F night are better than even. Between Apr 30 and May 13, the risk falls from 50% to 10%. Cool-season crops like peas and lettuce can go in weeks earlier; see the planting calendar.

What temperature is a killing frost?

A light frost is enough to kill tender crops such as tomatoes. CSU Extension describes 28–32°F as a light frost and anything below 28°F as a heavy frost. We report NOAA odds at three thresholds: 36°F (frost possible on plants), 32°F (freeze, our headline) and 28°F (hard freeze).

Is first frost the same as first freeze?

Not quite. A freeze is when the air reaches 32°F. Frost is ice that forms on surfaces, and on calm, clear nights it can form with the air a few degrees above freezing. So in Denver, the first 36°F night (frost possible on plants) typically comes around Oct 4, before the first 32°F night (Oct 12).

Download & sources

• Add Denver frost & planting dates to your calendar (.ics, 2027)
• Printable planting calendar (PDF)
• How these numbers are calculated

Data: NOAA NCEI U.S. Climate Normals 1991–2020 (annual/seasonal and daily normals, station USC00052223); USDA Plant Hardiness Zone ZIP tables 2023 and 2012 by the PRISM Group, Oregon State University; Census 2020 ZIP/place relationship file; USGS elevation. Long-term odds, not a forecast. Figures and sentences are generated from these data by fixed rules; see the methodology. Last updated 2026-10-08.