Aurora, Colorado Frost Dates, Growing Season & Hardiness Zone

When is the last frost in Aurora?

In half of years, the last 32°F night has passed by May 7. In 1 year out of 10, one still comes after May 21. The last 36°F night (frost possible on plants) typically comes later, around May 18, and the last 28°F hard freeze earlier, around Apr 29.

Aurora has a long late-frost tail: 14 days separate the typical date (May 7) from the safer 1-in-10 date (May 21). If tender plants go out early, be ready to protect them on cold nights.

The typical last 36°F night (frost possible on plants in low spots) comes around May 18, 11 days after the typical last 32°F night. On clear, calm nights, frost can form on leaves even when the thermometer reads above freezing.

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

Mother's Day is the usual planting signal for many gardeners around Aurora (CSU PlantTalk). In 2027 that's May 9. As of that date, NOAA 1991–2020 normals at Cherry Creek Dam give between 40% and 50% odds of another 32°F night and between 80% and 90% odds of another 36°F night (frost possible on plants).

Is it too early to plant in Aurora?

Before May 7 the odds of another 32°F night are better than even; after May 21 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 Aurora?

By Oct 8, half of years have had their first 32°F night. In 1 year out of 10, it comes as early as Sep 25. In a typical year, look for the first 36°F night (frost possible on plants) around Sep 30 and the first 28°F hard freeze around Oct 15.

For fall crops, count back from Oct 8, or from Sep 25 to be safe. Our planting calendar does the math for each crop.

How long is Aurora's growing season?

Aurora's frost-free season (32°F) typically runs 152 days. In about 1 year out of 10, it's shorter than 133 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 2,800 a year (base 50°F).

How does Aurora's season compare?

Of the 20 Colorado cities with frost dates on this site, Aurora has a typical frost-free season of 152 days, which is the 14th longest.

Among the 56 U.S. cities with frost dates on this site, the typical frost-free season here is longer than in 6 of them and shorter than in 49.

Growing degree days (base 50°F)

Annual normal: 2,800 GDD (NOAA flag R, 11 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 Aurora? (USDA 2023)

On the 2023 USDA map, Aurora is zone 6a (-10 to -5°F average coldest winter night). On the 2012 map, most of the city was 5b. Of the 11 city ZIPs listed in both tables, 9 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 Aurora'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. Aurora'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 Aurora frost dates differ between websites?

You may see May 12 given as Aurora'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 May 7, the 50% (median) date.

The 'safer' date, May 21, is the 10%-risk date. A 32°F night after it happens in only about 1 year in 10.

You may also see May 18. That's the 50% date for a 36°F night (frost possible on plants) rather than a 32°F freeze, so sites using 36°F as their cutoff list later dates.

Sites also pick different weather stations. Within 25 miles of the city center, the 10 stations that meet our quality rules put the typical (50%) last 32°F frost anywhere from Apr 30 to May 9 (table below).

Which weather station is this based on?

Station

Cherry Creek Dam (NOAA USC00051547, COOP)

Distance

8.3 mi SW of the city center

Elevation

5,647 ft; city center 5,545 ft (USGS), difference +102 ft

Record

NOAA completeness flag R, 13 of 30 years (1991–2020)

Confidence

Medium (rule)

Confidence: Medium. The station passes our quality rules, but it's farther away or at a different elevation than ideal (8.3 mi, +102 ft; NOAA flag R, 13 of 30 years).

Caveat: NOAA flags this station's frost statistics 'R' (representative). They rest on 13 of the 30 years in 1991–2020, with missing months filled in from surrounding stations. The nearest station with a full 'S' (standard) record is Denver-Stapleton, 8.7 mi away; its typical last frost is May 4.

Aurora planting dates at a glance

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

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

Frost dates near Aurora

All Colorado cities

Frequently asked questions

What is the average last frost date in Aurora?

Based on NOAA 1991–2020 normals at Cherry Creek Dam, Aurora's typical last 32°F night is May 7. That's the median (50%) date. For a safer target, go with May 21, after which a freeze comes in only about 1 year in 10.

When is the first frost in Aurora?

Expect the first 32°F night by Oct 8 in a typical year, and as early as Sep 25 in about 1 year out of 10. Cold 36°F nights (frost possible on plants) typically start around Sep 30.

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

Aurora 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 Aurora?

For frost-tender plants, yes if it's before May 7: until then, the odds of another 32°F night are better than even. Between May 7 and May 21, 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?

It depends on the crop. Tender plants such as tomatoes are killed by a light frost, which CSU Extension describes as 28–32°F; below 28°F is a heavy frost. We show NOAA odds for 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 exactly. A freeze is about the air reaching 32°F. Frost is ice on surfaces, which can form on calm, clear nights while the air is still a few degrees above freezing. So in Aurora, the first 36°F night (frost possible on plants) typically comes around Sep 30, ahead of the first 32°F night (Oct 8).

Download & sources

• Add Aurora 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 USC00051547); 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.