Littleton, Colorado Frost Dates, Growing Season & Hardiness Zone
Frost odds and planting zone for Littleton for the 2027 season, based on 1991–2020 normals.
Last frost date
May 2
typical (50% chance of a later 32°F night)
Safer date: May 17 (10% risk)
earlyMay 2
typicalMay 17
safer
First fall frost
Oct 11
typical (50% chance it has happened by then)
Early-risk date: Sep 27 (10%)
Growing season
160 days
typical frost-free (32°F) season
Short year: 139 days (1 year in 10 is shorter)
USDA hardiness zone
5b–6a
2023 map: -15 to -5°F average coldest night
2012 map: 5b (most of the city)
Stations around the metro don't all agree. The typical last frost is as early as Apr 30 at Denver Water Dept. and as late as May 16 at Strontia Springs Dam.
Half of years have their last 32°F night by May 2. In 1 year out of 10, a freeze still comes after May 17.
Based on NOAA station Marston Filter Plant (USC00055402), 3.2 mi NW, elevation 5,610 ft (+182 ft vs. city center). Confidence: Medium.
When is the last frost in Littleton?
The typical last 32°F night is May 2, and in 1 year out of 10 a freeze still comes after May 17. Cold 36°F nights (frost possible on plants) typically last longer, to around May 12. The last hard freeze (28°F) typically comes earlier, around Apr 23.
In Littleton, late frosts can come well after the typical date. The safer 1-in-10 date (May 17) is 15 days after the typical date (May 2). Tender plants set out early will need cover on cold nights.
Cool nights hang on after the last freeze: the typical last 36°F night (frost possible on plants in low spots) is around May 12, 10 days later than the typical last 32°F night. Frost can form on leaves on clear, calm nights even with the thermometer above freezing.
| Threshold | 10% (safer) | 30% | 50% (typical) | 90% (early) |
|---|---|---|---|---|
| 36°F (frost possible on plants) | May 29 | May 18 | May 12 | Apr 30 |
| 32°F freeze | May 17 | May 8 | May 2 | Apr 20 |
| 28°F hard freeze | May 7 | Apr 29 | Apr 23 | Apr 8 |
All probabilities (10–90%)
| Threshold | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F (frost possible on plants) | May 29 | May 22 | May 18 | May 15 | May 12 | May 9 | May 7 | May 4 | Apr 30 |
| 32°F freeze | May 17 | May 12 | May 8 | May 5 | May 2 | Apr 30 | Apr 28 | Apr 25 | Apr 20 |
| 28°F hard freeze | May 7 | May 2 | Apr 29 | Apr 26 | Apr 23 | Apr 20 | Apr 17 | Apr 14 | Apr 8 |
Is it safe to plant after Mother's Day in Littleton?
Mother's Day is the usual planting signal for many gardeners around Littleton (CSU PlantTalk). In 2027 that's May 9. As of that date, NOAA 1991–2020 normals at Marston Filter Plant give between 20% and 30% odds of another 32°F night and about 60% odds of another 36°F night (frost possible on plants).
Is it too early to plant in Littleton?
Before May 2 the odds of another 32°F night are better than even; after May 17 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 Littleton?
By Oct 11, half of years have had their first 32°F night. In 1 year out of 10, it comes as early as Sep 27. In a typical year, look for the first 36°F night (frost possible on plants) around Oct 2 and the first 28°F hard freeze around Oct 21.
For fall crops, count back from Oct 11, or from Sep 27 to be safe. Our planting calendar does the math for each crop.
| Threshold | 10% (early) | 30% | 50% (typical) | 90% (late) |
|---|---|---|---|---|
| 36°F (frost possible on plants) | Sep 17 | Sep 27 | Oct 2 | Oct 15 |
| 32°F freeze | Sep 27 | Oct 5 | Oct 11 | Oct 23 |
| 28°F hard freeze | Oct 6 | Oct 15 | Oct 21 | Nov 5 |
All probabilities (10–90%)
| Threshold | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F (frost possible on plants) | Sep 17 | Sep 23 | Sep 27 | Sep 30 | Oct 2 | Oct 4 | Oct 7 | Oct 11 | Oct 15 |
| 32°F freeze | Sep 27 | Oct 1 | Oct 5 | Oct 7 | Oct 11 | Oct 14 | Oct 17 | Oct 19 | Oct 23 |
| 28°F hard freeze | Oct 6 | Oct 11 | Oct 15 | Oct 18 | Oct 21 | Oct 24 | Oct 27 | Oct 31 | Nov 5 |
How long is Littleton's growing season?
In a typical year, Littleton gets 160 days between the last and first 32°F nights. About 1 year in 10, the season is shorter than 139 days.
A season this long fits most warm-season vegetables planted on time. Long-season crops do best when started from transplants.
The station averages 2,772 growing degree days (base 50°F) a year. That number measures how much heat crops have to grow on.
| Threshold | 10% (long year) | 50% (typical) | 90% (short year) |
|---|---|---|---|
| 36°F (frost possible on plants) | 160 days | 142 days | 120 days |
| 32°F freeze | 181 days | 160 days | 139 days |
| 28°F hard freeze | 200 days | 180 days | 160 days |
How does Littleton's season compare?
Among the 20 Colorado cities with frost dates on this site, the typical frost-free season in Littleton (160 days) is tied for the 4th longest.
Among the 56 U.S. cities with frost dates on this site, the typical frost-free season here is longer than in 13 of them and shorter than in 39.
Growing degree days (base 50°F)
Annual normal: 2,772 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):
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 4 | 30 | 99 | 340 | 854 | 1,565 | 2,224 | 2,622 | 2,743 | 2,768 | 2,770 |
What growing zone is Littleton? (USDA 2023)
The 2023 USDA map puts Littleton in zone 5b–6a (-15 to -5°F average coldest winter night). On the 2012 map, most of the city was 5b. Comparing ZIPs listed in both tables, 7 of 8 moved up half a zone.
| ZIP | 2023 | 2012 | Change | Share of ZIP in Littleton |
|---|---|---|---|---|
| 80110 | 6a | 5b | +1 half zone (warmer) | 0% |
| 80120 mostly in city | 6a | 5b | +1 half zone (warmer) | 98% |
| 80121 | 6a | 5b | +1 half zone (warmer) | 4% |
| 80122 | 6a | 5b | +1 half zone (warmer) | 10% |
| 80123 | 6a | 5b | +1 half zone (warmer) | 16% |
| 80127 | 5b | 5b | unchanged | 1% |
| 80128 | 6a | 5b | +1 half zone (warmer) | 6% |
| 80129 | 6a | 5b | +1 half zone (warmer) | 3% |
Other ZIPs touching Littleton
ZIPs outside the 801 prefix that overlap the city boundary:
- none
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 Littleton'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. Littleton'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 Littleton frost dates differ between websites?
If you've seen May 8 listed as Littleton's last frost date, that's the 30%-risk date: about 3 years in 10 still get a 32°F night after it. We lead with May 2, the 50% (median) date.
May 17 is the 10%-risk, or 'safer', date. Only about 1 year in 10 has a 32°F night after it.
May 12 is the typical (50%) date for a 36°F night (frost possible on plants), not a 32°F freeze. Any site that draws the line at 36°F will show later dates.
Station choice is another reason dates differ. Our 12 qualifying stations within 25 miles of the city center range from Apr 30 to May 16 for the typical (50%) last 32°F frost (table below).
| Date | What it is (NOAA 1991–2020) |
|---|---|
| May 8 | 32°F last frost, 30% risk (a 'balanced' date) |
| May 12 | 36°F last cold night, 50% (frost possible on plants) |
| May 17 | 32°F last frost, 10% risk (the 'safer' date) |
| Apr 23 | 28°F last hard freeze, 50% |
| May 5 | 32°F last frost, 50%, at Wheat Ridge 2 (nearest station with NOAA flag S) |
| Station | Distance | Elevation | Typical last frost |
|---|---|---|---|
| Denver Water Dept. | 9.6 mi N | 5,228 ft | Apr 30 |
| Marston Filter Plant used here | 3.2 mi NW | 5,610 ft | May 2 |
| Northglenn | 21.3 mi N | 5,407 ft | May 2 |
| Lakewood | 12.2 mi NNW | 5,640 ft | May 3 |
| Ralston Reservoir | 20.1 mi NW | 5,900 ft | May 3 |
| Denver-Stapleton | 14.4 mi NE | 5,286 ft | May 4 |
| Denver Centennial Airport | 9.2 mi E | 5,883 ft | May 5 |
| Wheat Ridge 2 | 13.8 mi NNW | 5,398 ft | May 5 |
| Cherry Creek Dam | 10.3 mi ENE | 5,647 ft | May 7 |
| Kassler | 8.0 mi SSW | 5,587 ft | May 8 |
| Parker | 15.3 mi ESE | 5,904 ft | May 9 |
| Strontia Springs Dam | 12.0 mi SSW | 5,840 ft | May 16 |
Which weather station is this based on?
- Station
- Marston Filter Plant (NOAA USC00055402, COOP)
- Distance
- 3.2 mi NW of the city center
- Elevation
- 5,610 ft; city center 5,428 ft (USGS), difference +182 ft
- Record
- NOAA completeness flag R, 18 of 30 years (1991–2020)
- Confidence
- Medium (rule)
Confidence: Medium. The station passes our quality rules but isn't an ideal match: 3.2 mi away, +182 ft elevation difference (NOAA flag R, 18 of 30 years).
Caveat: NOAA flags this station's frost statistics 'R' (representative). They rest on 18 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 Wheat Ridge 2, 13.8 mi away; its typical last frost is May 5.
| Station | ID | Distance | Elev. (Δ) | Last frost 50% | First frost 50% | Season 50% | NOAA flag / years |
|---|---|---|---|---|---|---|---|
| Marston Filter Plant | USC00055402 | 3.2 mi NW | 5,610 ft (+182) | May 2 | Oct 11 | 160 d | R / 18 |
| Kassler | USC00054452 | 8.0 mi SSW | 5,587 ft (+159) | May 8 | Oct 3 | 147 d | R / 23 |
| Denver Centennial Airport | USW00093067 | 9.2 mi E | 5,883 ft (+455) | May 5 | Oct 8 | 154 d | R / 20 |
| Denver Water Dept. | USC00052223 | 9.6 mi N | 5,228 ft (-200) | Apr 30 | Oct 12 | 165 d | R / 22 |
| Cherry Creek Dam | USC00051547 | 10.3 mi ENE | 5,647 ft (+219) | May 7 | Oct 8 | 152 d | R / 13 |
| Strontia Springs Dam | USC00058022 | 12.0 mi SSW | 5,840 ft (+412) | May 16 | Sep 29 | 132 d | R / 19 |
| Lakewood | USC00054762 | 12.2 mi NNW | 5,640 ft (+212) | May 3 | Oct 7 | 155 d | R / 24 |
| Wheat Ridge 2 | USC00058995 | 13.8 mi NNW | 5,398 ft (-30) | May 5 | Oct 5 | 151 d | S / 28 |
| Denver-Stapleton | USW00023062 | 14.4 mi NE | 5,286 ft (-142) | May 4 | Oct 8 | 156 d | S / 28 |
| Parker | USC00056323 | 15.3 mi ESE | 5,904 ft (+476) | May 9 | Oct 3 | 145 d | R / 16 |
| Ralston Reservoir | USC00056816 | 20.1 mi NW | 5,900 ft (+472) | May 3 | Oct 14 | 161 d | R / 22 |
| Northglenn | USC00055984 | 21.3 mi N | 5,407 ft (-21) | May 2 | Oct 11 | 160 d | S / 26 |
Other stations within 25 mi (not used)
- Roxborough State Park (USC00057249), 11.5 mi SSW, 6,117 ft: typical last frost May 16. Not used: |elev diff| 689 ft > 500 ft.
- Castle Rock (USC00051401), 13.8 mi SSE, 6,185 ft: typical last frost May 9. Not used: |elev diff| 757 ft > 500 ft.
- Evergreen (USC00052790), 16.0 mi WNW, 6,985 ft: typical last frost May 23. Not used: |elev diff| 1557 ft > 500 ft.
76 other NOAA normals stations within 40 km (mostly rain gauges) have no frost statistics.
Littleton planting dates at a glance
Balanced dates use the 30%-risk last-frost date as the anchor. The Littleton planting calendar has typical and safe dates, fall planting and a month-by-month list for 27 vegetables.
| Crop | Start indoors | Plant outdoors (balanced) | Fall |
|---|---|---|---|
| Tomatoes | Apr 23 – May 7 | Jun 11 | – |
| Peppers | Mar 27 – Apr 10 | May 22 | – |
| Potatoes | – | Apr 24 – May 8 | – |
| Onions (dry, from sets) | – | Apr 10–24 | – |
| Peas | – | Apr 10–24 | sow by Jul 24 |
| Lettuce (leaf) | – | Apr 10–24 | sow by Jul 29 |
| Carrots | – | Apr 24 – May 8 | sow by Jul 19 |
| Beans (snap) | – | May 8 | sow by Jul 15 |
| Summer squash | – | May 8 | sow by Jul 25 |
| Broccoli | Feb 20 – Mar 6 | Apr 10–24 | transplant by Jul 24 |
| Cabbage | Feb 20 – Mar 6 | Apr 10–24 | transplant by Jul 4 |
| Cauliflower | Mar 6–20 | Apr 24 – May 8 | – |
| Kohlrabi | – | Apr 10–24 | sow by Aug 8 |
| Green onions | – | Apr 10–24 | sow by Jul 29 |
| Radishes | – | Apr 10–24 | sow by Aug 28 |
| Spinach | – | Apr 10–24 | sow by Aug 18 |
| Turnips | – | Apr 10–24 | sow by Aug 8 |
| Beets | – | Apr 24 – May 8 | sow by Jul 29 |
| Swiss chard | – | Apr 24 – May 8 | sow by Jul 29 |
| Parsnips | – | Apr 24 – May 8 | – |
| Sweet corn | – | May 8 | – |
| Cucumbers | – | May 8 | sow by Jul 20 |
| Eggplant | Mar 20 – Apr 10 | May 22 | – |
| Cantaloupe | – | May 22 | – |
| Watermelon | – | May 22 | – |
| Winter squash | – | May 22 | – |
| Garlic | – | – | plant Oct 1–14 |
When to plant tomatoes in Littleton · Fall planting dates for Littleton
Frost dates near Littleton
| City | Distance | Last frost | First frost | Season | Zone 2023 |
|---|---|---|---|---|---|
| Centennial frost dates | 8 mi | May 5 | Oct 8 | 154 days | 6a |
| Lakewood frost dates | 9 mi | May 3 | Oct 7 | 155 days | 6a |
| Denver frost dates | 10 mi | Apr 30 | Oct 12 | 165 days | 6a |
| Parker frost dates | 14 mi | May 9 | Oct 3 | 145 days | 5b–6a |
| Castle Rock frost dates | 17 mi | May 9 | Oct 2 | 143 days | 5b |
| Aurora frost dates | 18 mi | May 7 | Oct 8 | 152 days | 6a |
Frequently asked questions
What is the average last frost date in Littleton?
The typical (median, 50%) last 32°F night in Littleton is May 2, based on NOAA 1991–2020 normals at Marston Filter Plant. For a safer target, use May 17; after that, only about 1 year in 10 still has a freeze.
When is the first frost in Littleton?
Typically by Oct 11 for the first 32°F night, though about 1 year in 10 it comes as early as Sep 27. The first 36°F night (frost possible on plants) typically shows up around Oct 2.
What growing zone is Littleton, Colorado? Is Littleton zone 5 or 6?
Littleton is in USDA hardiness zone 5b–6a on the current 2023 map (zone 5–6 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 Littleton?
For frost-tender plants, yes if it's before May 2: until then, the odds of another 32°F night are better than even. Between May 2 and May 17, 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 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 Littleton, the first 36°F night (frost possible on plants) typically comes around Oct 2, before the first 32°F night (Oct 11).
Download & sources
- Add Littleton 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 USC00055402); 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.