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Frost dates and planting calendar for Aurora, Colorado

Updated October 30, 2026. Based on USDA, NOAA and Colorado State University Extension data. Published by Humblebee.

USDA hardiness zone
6a[1]
Median last spring frost
May 4[2]
Median first fall frost
Oct 8[3]
Growing season, median
156 days[4]

Aurora, Colorado is in USDA hardiness zone 6a on the 2023 map[1]. The median last spring frost at the nearest NOAA station is May 4[2].

Frost dates

JanFebMarAprMayJunJulAugSepOctNovDecLast spring frost: 9 in 10 years after Apr 20, half of years May 4, 1 in 10 years after May 16Last frostmedian May 4First fall frost: 9 in 10 years before Oct 20, half of years Oct 8, 1 in 10 years before Sep 25First frostmedian Oct 8Frost riskHardyHardy vegetables: plant Apr 6 to Apr 20Apr 6 to Apr 20Semi-hardySemi-hardy vegetables: plant Apr 20 to May 4Apr 20 to May 4TenderTender vegetables: plant around May 4around May 4Very tenderVery tender vegetables: plant from May 18from May 18
Shaded: the span between the dates frost passes in 9 of 10 years and 1 of 10 years[2][3]. Green: planting windows from the CSU rules applied to the median last frost (GardenFacts calculation)[6]. Exact dates are in the tables below.

These dates come from NOAA climate normals for the Denver-Stapleton weather station, using records from 1991 to 2020[5]. In half of years the last spring frost comes after May 4, and in 1 of 10 years it comes after May 16[2]. In 9 of 10 years the last frost comes after April 20[2]. In the fall, the median first frost is October 8, and in 1 of 10 years it comes before September 25[3]. These are odds from past years and not a forecast, so any year can be earlier or later[5].

Frost Likely (9 in 10 years) Even odds (5 in 10) Unlikely (1 in 10)
Last spring frost (32°F)[2] after April 20 after May 4 after May 16
First fall frost (32°F)[3] before September 25 before October 8 before October 20
  • Hard freeze (28°F): median last spring date April 22, median first fall date October 18[7].
  • Frost-free growing season: at least 138 days in 9 of 10 years, 156 days in half of years and 175 days in 1 of 10 years[4].
  • The low reached 32°F or colder in 100% of years and 28°F or colder in 100% of years[8].
  • Weather station: Denver-Stapleton (USW00023062), 8.7 miles from the city center, 5,286 feet, 28 years of 1991 to 2020 records[5].

When to plant vegetables

Colorado State University Extension groups vegetables by how well they handle cold, and its guide was written for Colorado[6]. Hardy vegetables such as lettuce, peas and spinach can go in as early as 2 to 4 weeks before the median last frost, which is April 6 to April 20 here[6]. Semi-hardy vegetables such as carrots and potatoes can go in as early as 2 weeks before the median last frost, which is April 20[9]. Tender vegetables such as snap beans and sweet corn can be seeded around the median last frost date, May 4[10]. Very tender vegetables such as tomatoes and peppers typically wait 2 or more weeks after the median last frost, so the earliest start is May 18[11].

  • Hardy (broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips): as early as 2 to 4 weeks before the median last frost (May 4) is April 6 to April 20[6]
  • Semi-hardy (beets, carrots, cauliflower, parsnips, potatoes, Swiss chard): as early as 2 weeks before the median last frost (May 4) is April 20, up to the median date itself[9]
  • Tender (snap beans, sweet corn, cucumbers, summer squash): from seed around the median last frost date, May 4[10]
  • Very tender (cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon): the earliest start, two weeks after the median last frost (May 4), is May 18[11]
Vegetable (CSU group) Plant from First harvest around
Broccoli (hardy)[12] Apr 6 Jun 10 (from transplants)
Cabbage (hardy)[12] Apr 6 Jun 30 (from transplants)
Kohlrabi (hardy)[12] Apr 6 May 26
Lettuce (hardy)[12] Apr 6 Jun 5
Onions (hardy)[12] Apr 6 Jul 25
Peas (hardy)[12] Apr 6 Jun 10
Radishes (hardy)[12] Apr 6 May 6
Spinach (hardy)[12] Apr 6 May 16
Turnips (hardy)[12] Apr 6 May 26
Beets (semi-hardy)[12] Apr 20 Jun 19
Carrots (semi-hardy)[12] Apr 20 Jun 29
Cauliflower (semi-hardy)[12] Apr 20 not listed
Parsnips (semi-hardy)[12] Apr 20 Jun 29
Potatoes (semi-hardy)[12] Apr 20 Aug 23
Swiss chard (semi-hardy)[12] Apr 20 Jun 19
Snap beans (tender)[12] May 4 Jul 3
Sweet corn (tender)[12] May 4 Jul 3
Cucumbers (tender)[12] May 4 Jun 28
Summer squash (tender)[12] May 4 Jun 23
Cantaloupe (very tender)[12] May 18 Aug 11
Eggplant (very tender)[12] May 18 Jul 17 (from transplants)
Peppers (very tender)[12] May 18 Jul 27 (from transplants)
Tomatoes (very tender)[12] May 18 Jul 22 (from transplants)
Winter squash (very tender)[12] May 18 Aug 26
Watermelon (very tender)[12] May 18 Aug 11
Spacing, depth and soil temperature (CSU Extension)
Vegetable Min. soil temp Depth Spacing Days to harvest
Broccoli[13] 40°F 1/2 in 18 in 65
Cabbage[13] 40°F 1/2 in 18 in 85
Kohlrabi[13] 40°F 1/2 in 7-9 in 50
Lettuce[13] 35°F 1/4 in 7-9 in 60
Onions[13] 35°F 1/4 in (seed), 1-2 in (sets) 4-6 in 110
Peas[13] 40°F 1 in 4-6 in 65
Radishes[13] 40°F 1/2 in 2-3 in 30
Spinach[13] 40°F 1/2 in 4-6 in 40
Turnips[13] 40°F 1/2 in 4-6 in 50
Beets[13] 40°F 3/4-1 in 4-6 in 60
Carrots[13] 40°F 1/4 in 2-3 in 70
Cauliflower[13] 40°F 1/2 in 18 in –
Parsnips[13] 35°F 1/2 in 5-6 in 70
Potatoes[13] 45°F – – 125
Swiss chard[13] 40°F 1 in 7-9 in 60
Snap beans[13] 55°F 1-1 1/2 in 6 in 60
Sweet corn[13] 50°F 1-1 1/2 in 12 x 30 in or 9 x 36 in 60-90
Cucumbers[13] 60°F 1 in 6 in trellised, 24-36 in untrellised 55
Summer squash[13] 60°F 1-1 1/2 in 36-48 in 50
Cantaloupe[13] 60°F 1-1 1/2 in 36-48 in 85
Eggplant[13] 60°F 1/4 in 18-24 in 60
Peppers[13] 60°F 1/4 in 15-18 in 70
Tomatoes[13] 50°F 1/4 in 24 in trellised 65
Winter squash[13] 60°F 1-1 1/2 in 36-48 in 100
Watermelon[13] 60°F 1-1 1/2 in 36-48 in 85

Hardiness zone

The zone number is based on the average coldest night of each winter from 1991 to 2020, not on summer heat or frost dates[14]. Zone 6a means an average annual extreme minimum of -10°F to -5°F[1]. Aurora overlaps 20 ZIP code areas, and 99% of the city's land area lies in ZIP code areas rated zone 6a[15].

Zone 6a: average annual extreme minimum temperature -10°F to -5°F (1991 to 2020)[1]. Modeled value at the city center: -8.2°F[1].

Share of the city's land area by ZIP code zone: zone 6a 99%[15].

All towns in zone 6a and what zone 6a means

Zone by ZIP code
ZIP code Zone Coldest night range
80137[15] 6a -10 to -5°F
80019[15] 6a -10 to -5°F
80018[15] 6a -10 to -5°F
80016[15] 6a -10 to -5°F
80011[15] 6a -10 to -5°F
80013[15] 6a -10 to -5°F
80017[15] 6a -10 to -5°F
80012[15] 6a -10 to -5°F
80014[15] 6a -10 to -5°F
80010[15] 6a -10 to -5°F
80015[15] 6a -10 to -5°F
80102[15] 6a -10 to -5°F
80045[15] 6a -10 to -5°F
80138[15] 5b -15 to -10°F
80247[15] 6a -10 to -5°F
80230[15] 6a -10 to -5°F
80112[15] 6a -10 to -5°F
80239[15] 6a -10 to -5°F
80231[15] 6a -10 to -5°F
80220[15] 6a -10 to -5°F

Questions people ask

What growing zone is Aurora, Colorado?
The center of Aurora is in USDA zone 6a on the 2023 map[1]. By land area, 99% of the city lies in ZIP code areas rated zone 6a[15].
When is the last frost in Aurora?
The median last spring frost is May 4, so in half of years the last frost comes after that date[2]. In 1 of 10 years it comes after May 16[2].
When to plant tomatoes in Aurora?
Colorado State University Extension lists tomatoes as very tender and says typically 2 or more weeks after the average last frost[11]. Using the median last frost, the earliest start is May 18[11].
When is the first frost in Aurora?
The median first fall frost is October 8[3]. In 1 of 10 years it comes before September 25[3].
How long is the growing season in Aurora?
The growing season is at least 156 days in half of years[4]. It is at least 138 days in 9 of 10 years[4].

Facts and sources

  1. The 2023 USDA Plant Hardiness Zone Map puts the center of Aurora, Colorado in zone 6a. Zone 6a means an average annual extreme minimum temperature of -10°F to -5°F over 1991 to 2020. The map's modeled value at the city center is minus 8.2°F. USDA zone map 2023 (PRISM, OSU)
  2. Last spring frost (32°F) at this station: in 9 of 10 years the last frost comes after April 20, in half of years after May 4, and in 1 of 10 years after May 16 (NOAA 1991 to 2020 normals). The median last frost date is May 4. NOAA Climate Normals 1991-2020
  3. First fall frost (32°F) at this station: in 1 of 10 years the first frost comes before September 25, in half of years before October 8, and in 9 of 10 years before October 20 (NOAA 1991 to 2020 normals). The median first frost date is October 8. NOAA Climate Normals 1991-2020
  4. Growing season (days between the last spring and first fall 32°F frost) at this station: at least 138 days in 9 of 10 years, at least 156 days in half of years, and at least 175 days in 1 of 10 years. NOAA Climate Normals 1991-2020
  5. Frost dates on this page come from NOAA climate normals for the Denver-Stapleton weather station (USW00023062), 8.7 miles from the center of Aurora at 5,286 feet, using 28 years of records from 1991 to 2020. NOAA Climate Normals 1991-2020
  6. Colorado State University Extension's vegetable planting guide (written for Colorado) groups broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips as hardy vegetables, with this rule: as early as 2-4 weeks before the average last... CSU Extension GardenNotes #720
  7. Hard freeze (28°F) at this station: the median last spring date is April 22 and the median first fall date is October 18. NOAA Climate Normals 1991-2020
  8. At this station the low reached 32°F or colder in 100% of years from 1991 to 2020, and 28°F or colder in 100% of years. NOAA Climate Normals 1991-2020
  9. Colorado State University Extension's vegetable planting guide (written for Colorado) groups beets, carrots, cauliflower, parsnips, potatoes, Swiss chard as semi-hardy vegetables, with this rule: as early as 0-2 weeks before the average last spring frost.... CSU Extension GardenNotes #720
  10. Colorado State University Extension's vegetable planting guide (written for Colorado) groups snap beans, sweet corn, cucumbers, summer squash as tender vegetables, with this rule: from seed around the average last spring frost; cucumber and summer squash... CSU Extension GardenNotes #720
  11. Colorado State University Extension's vegetable planting guide (written for Colorado) groups cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon as very tender vegetables, with this rule: typically 2 or more weeks after the average last... CSU Extension GardenNotes #720
  12. GardenFacts calculation: earliest planting date plus CSU days to harvest (table on this page), from the station's median last frost. NOAA Climate Normals 1991-2020
  13. CSU Extension vegetable table: soil temperature, depth, spacing, days to harvest (table on this page). CSU Extension GardenNotes #720
  14. USDA hardiness zones are based on the average annual extreme minimum winter temperature (the coldest night of each winter, averaged over 1991 to 2020 for the 2023 map), not on summer heat or frost dates. Each zone spans 10°F and each half zone (a or b)... USDA Plant Hardiness Zone Map
  15. Aurora, Colorado overlaps 20 ZIP code areas. By land area, 99% lies in ZIP code areas rated zone 6a. USDA zone map 2023 (PRISM, OSU)

Frost dates are probabilities from 1991 to 2020 weather records at one NOAA station, not a forecast. Any year can be earlier or later. The hardiness zone describes the average coldest winter night, not frost dates or summer heat. Spots inside the city can differ (ZIP table). Planting rules come from Colorado State University Extension's guide, written for Colorado. A local extension office may give dates tuned to the area. Planting and harvest dates marked GardenFacts calculation are simple arithmetic from the facts above, not advice from the source.

Hardiness zone data: USDA Plant Hardiness Zone Map (2023), USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu, accessed October 30, 2026. This is not the official USDA map. Frost data: NOAA NCEI U.S. Climate Normals 1991-2020. Planting rules: Colorado State University Extension.