Parker, Colorado Frost Dates, Growing Season & Hardiness Zone
Frost odds and planting zone for Parker for the 2027 season, based on 1991–2020 normals.
Last frost date
May 9
typical (50% chance of a later 32°F night)
Safer date: May 23 (10% risk)
earlyMay 9
typicalMay 23
safer
First fall frost
Oct 3
typical (50% chance it has happened by then)
Early-risk date: Sep 21 (10%)
Growing season
145 days
typical frost-free (32°F) season
Short year: 127 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)
Where you live in the metro matters. The typical last frost ranges from May 2 at Marston Filter Plant to May 16 at Roxborough State Park.
Half of years have their last 32°F night by May 9. In 1 year out of 10, a freeze still comes after May 23.
Based on NOAA station Parker (USC00056323), 1.5 mi ENE, elevation 5,904 ft (+58 ft vs. city center). Confidence: Medium.
When is the last frost in Parker?
Expect the last 32°F night by May 9 in a typical year; 1 year in 10 still freezes after May 23. Cold 36°F nights (frost possible on plants) typically last longer, until around May 20. Hard freezes (28°F) typically end sooner, around Apr 29.
In Parker, late frosts can come well after the typical date. The safer 1-in-10 date (May 23) is 14 days after the typical date (May 9). 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 20, 11 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) | Jun 2 | May 25 | May 20 | May 8 |
| 32°F freeze | May 23 | May 14 | May 9 | Apr 27 |
| 28°F hard freeze | May 12 | May 4 | Apr 29 | Apr 15 |
All probabilities (10–90%)
| Threshold | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F (frost possible on plants) | Jun 2 | May 29 | May 25 | May 23 | May 20 | May 18 | May 14 | May 11 | May 8 |
| 32°F freeze | May 23 | May 18 | May 14 | May 12 | May 9 | May 6 | May 4 | May 1 | Apr 27 |
| 28°F hard freeze | May 12 | May 7 | May 4 | May 2 | Apr 29 | Apr 27 | Apr 23 | Apr 19 | Apr 15 |
Is it safe to plant after Mother's Day in Parker?
Many Parker-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 about 50%, and the chance of another 36°F night (frost possible on plants) is between 80% and 90% (NOAA 1991–2020, Parker).
Is it too early to plant in Parker?
Before May 9 the odds of another 32°F night are better than even; after May 23 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 Parker?
By Oct 3, half of years have had their first 32°F night. In 1 year out of 10, it comes as early as Sep 21. In a typical year, look for the first 36°F night (frost possible on plants) around Sep 25 and the first 28°F hard freeze around Oct 12.
Fall plantings are timed backward from first frost: Oct 3 typically, or Sep 21 if you want a cushion. See the planting calendar for each crop's date.
| Threshold | 10% (early) | 30% | 50% (typical) | 90% (late) |
|---|---|---|---|---|
| 36°F (frost possible on plants) | Sep 12 | Sep 21 | Sep 25 | Oct 6 |
| 32°F freeze | Sep 21 | Sep 28 | Oct 3 | Oct 15 |
| 28°F hard freeze | Sep 29 | Oct 6 | Oct 12 | Oct 23 |
All probabilities (10–90%)
| Threshold | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F (frost possible on plants) | Sep 12 | Sep 18 | Sep 21 | Sep 23 | Sep 25 | Sep 28 | Sep 30 | Oct 2 | Oct 6 |
| 32°F freeze | Sep 21 | Sep 25 | Sep 28 | Oct 1 | Oct 3 | Oct 5 | Oct 7 | Oct 11 | Oct 15 |
| 28°F hard freeze | Sep 29 | Oct 3 | Oct 6 | Oct 9 | Oct 12 | Oct 15 | Oct 17 | Oct 19 | Oct 23 |
How long is Parker's growing season?
In a typical year, Parker gets 145 days between the last and first 32°F nights. About 1 year in 10, the season is shorter than 127 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 2,541 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) | 142 days | 126 days | 107 days |
| 32°F freeze | 163 days | 145 days | 127 days |
| 28°F hard freeze | 184 days | 165 days | 145 days |
How does Parker's season compare?
At 145 days, the typical frost-free season in Parker is the 18th longest among the 20 Colorado cities with frost dates on this site.
Compared with the 56 U.S. cities with frost dates on this site, this typical frost-free season is longer than in 2 and shorter than in 53.
Growing degree days (base 50°F)
Annual normal: 2,541 GDD (NOAA flag R, 12 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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 0 | 1 | 23 | 91 | 314 | 809 | 1,475 | 2,076 | 2,439 | 2,530 | 2,540 | 2,540 |
What growing zone is Parker? (USDA 2023)
The 2023 USDA map puts Parker 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, 1 of 3 moved up half a zone.
| ZIP | 2023 | 2012 | Change | Share of ZIP in Parker |
|---|---|---|---|---|
| 80112 | 6a | 5b | +1 half zone (warmer) | 0% |
| 80134 | 5b | 5b | unchanged | 28% |
| 80138 | 5b | 5b | unchanged | 10% |
Other ZIPs touching Parker
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 Parker's frost dates?
No. Zones describe only how cold the coldest winter night gets on average. They don't tell you when frost starts or stops. The frost dates for Parker come from NOAA's 1991–2020 frost probabilities, which the 2023 zone map left untouched. Choose winter-hardy perennials by zone, and schedule planting by frost dates.
Why do Parker frost dates differ between websites?
Some sources list May 14 for Parker. That's the 30%-risk date: about 3 years in 10 still see a 32°F night after it. We headline the 50% (median) date, May 9.
May 23 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 20 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.
Sites also pick different weather stations. Within 25 miles of the city center, the 9 stations that meet our quality rules put the typical (50%) last 32°F frost anywhere from May 2 to May 16 (table below).
| Date | What it is (NOAA 1991–2020) |
|---|---|
| May 14 | 32°F last frost, 30% risk (a 'balanced' date) |
| May 20 | 36°F last cold night, 50% (frost possible on plants) |
| May 23 | 32°F last frost, 10% risk (the 'safer' date) |
| Apr 29 | 28°F last hard freeze, 50% |
| May 9 | 32°F last frost, 50%, at Castle Rock (nearest station with NOAA flag S) |
| Station | Distance | Elevation | Typical last frost |
|---|---|---|---|
| Marston Filter Plant | 17.4 mi WNW | 5,610 ft | May 2 |
| Denver Centennial Airport | 5.9 mi NW | 5,883 ft | May 5 |
| Denver International Airport | 23.4 mi NNE | 5,414 ft | May 5 |
| Cherry Creek Dam | 8.8 mi NNW | 5,647 ft | May 7 |
| Kassler | 17.1 mi W | 5,587 ft | May 8 |
| Parker used here | 1.5 mi ENE | 5,904 ft | May 9 |
| Castle Rock | 9.6 mi SW | 6,185 ft | May 9 |
| Roxborough State Park | 16.6 mi WSW | 6,117 ft | May 16 |
| Strontia Springs Dam | 19.1 mi WSW | 5,840 ft | May 16 |
Which weather station is this based on?
- Station
- Parker (NOAA USC00056323, COOP)
- Distance
- 1.5 mi ENE of the city center
- Elevation
- 5,904 ft; city center 5,846 ft (USGS), difference +58 ft
- Record
- NOAA completeness flag R, 16 of 30 years (1991–2020)
- Confidence
- Medium (rule)
Confidence: Medium. The station passes our quality rules but isn't an ideal match: 1.5 mi away, +58 ft elevation difference (NOAA flag R, 16 of 30 years).
Note: NOAA rates this station's frost statistics 'R' (representative). That means they use 16 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, Castle Rock (9.6 mi away), has a typical last frost of May 9.
| Station | ID | Distance | Elev. (Δ) | Last frost 50% | First frost 50% | Season 50% | NOAA flag / years |
|---|---|---|---|---|---|---|---|
| Parker | USC00056323 | 1.5 mi ENE | 5,904 ft (+58) | May 9 | Oct 3 | 145 d | R / 16 |
| Denver Centennial Airport | USW00093067 | 5.9 mi NW | 5,883 ft (+37) | May 5 | Oct 8 | 154 d | R / 20 |
| Cherry Creek Dam | USC00051547 | 8.8 mi NNW | 5,647 ft (-199) | May 7 | Oct 8 | 152 d | R / 13 |
| Castle Rock | USC00051401 | 9.6 mi SW | 6,185 ft (+339) | May 9 | Oct 2 | 143 d | S / 25 |
| Roxborough State Park | USC00057249 | 16.6 mi WSW | 6,117 ft (+271) | May 16 | Oct 1 | 136 d | R / 24 |
| Kassler | USC00054452 | 17.1 mi W | 5,587 ft (-259) | May 8 | Oct 3 | 147 d | R / 23 |
| Marston Filter Plant | USC00055402 | 17.4 mi WNW | 5,610 ft (-236) | May 2 | Oct 11 | 160 d | R / 18 |
| Strontia Springs Dam | USC00058022 | 19.1 mi WSW | 5,840 ft (-6) | May 16 | Sep 29 | 132 d | R / 19 |
| Denver International Airport | USW00003017 | 23.4 mi NNE | 5,414 ft (-432) | May 5 | Oct 9 | 156 d | R / 25 |
Other stations within 25 mi (not used)
- Elizabeth 2 NW (USC00052631), 11.7 mi SE, 6,611 ft: typical last frost May 16. Not used: |elev diff| 765 ft > 500 ft.
- Denver-Stapleton (USW00023062), 18.5 mi NNW, 5,286 ft: typical last frost May 4. Not used: |elev diff| 560 ft > 500 ft.
- Denver Water Dept. (USC00052223), 19.8 mi NW, 5,228 ft: typical last frost Apr 30. Not used: |elev diff| 618 ft > 500 ft.
53 other NOAA normals stations within 40 km (mostly rain gauges) have no frost statistics.
Parker planting dates at a glance
Balanced dates use the 30%-risk last-frost date as the anchor. The Parker 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 | May 7–21 | Jun 25 | – |
| Peppers | Apr 2–16 | May 28 | – |
| Potatoes | – | Apr 30 – May 14 | – |
| Onions (dry, from sets) | – | Apr 16–30 | – |
| Peas | – | Apr 16–30 | sow by Jul 16 |
| Lettuce (leaf) | – | Apr 16–30 | sow by Jul 21 |
| Carrots | – | Apr 30 – May 14 | sow by Jul 11 |
| Beans (snap) | – | May 14 | sow by Jul 7 |
| Summer squash | – | May 14 | sow by Jul 17 |
| Broccoli | Feb 26 – Mar 12 | Apr 16–30 | transplant by Jul 16 |
| Cabbage | Feb 26 – Mar 12 | Apr 16–30 | transplant by Jun 26 |
| Cauliflower | Mar 12–26 | Apr 30 – May 14 | – |
| Kohlrabi | – | Apr 16–30 | sow by Jul 31 |
| Green onions | – | Apr 16–30 | sow by Jul 21 |
| Radishes | – | Apr 16–30 | sow by Aug 20 |
| Spinach | – | Apr 16–30 | sow by Aug 10 |
| Turnips | – | Apr 16–30 | sow by Jul 31 |
| Beets | – | Apr 30 – May 14 | sow by Jul 21 |
| Swiss chard | – | Apr 30 – May 14 | sow by Jul 21 |
| Parsnips | – | Apr 30 – May 14 | – |
| Sweet corn | – | May 14 | – |
| Cucumbers | – | May 14 | sow by Jul 12 |
| Eggplant | Mar 26 – Apr 16 | May 28 | – |
| Cantaloupe | – | May 28 | – |
| Watermelon | – | May 28 | – |
| Winter squash | – | May 28 | – |
| Garlic | – | – | plant Oct 1–14 |
When to plant tomatoes in Parker · Fall planting dates for Parker
Frost dates near Parker
| City | Distance | Last frost | First frost | Season | Zone 2023 |
|---|---|---|---|---|---|
| Centennial frost dates | 8 mi | May 5 | Oct 8 | 154 days | 6a |
| Castle Rock frost dates | 10 mi | May 9 | Oct 2 | 143 days | 5b |
| Littleton frost dates | 14 mi | May 2 | Oct 11 | 160 days | 5b–6a |
| Aurora frost dates | 14 mi | May 7 | Oct 8 | 152 days | 6a |
| Denver frost dates | 20 mi | Apr 30 | Oct 12 | 165 days | 6a |
| Lakewood frost dates | 23 mi | May 3 | Oct 7 | 155 days | 6a |
Frequently asked questions
What is the average last frost date in Parker?
The typical (median, 50%) last 32°F night in Parker is May 9, based on NOAA 1991–2020 normals at Parker. For a safer target, use May 23; after that, only about 1 year in 10 still has a freeze.
When is the first frost in Parker?
The first 32°F night typically arrives by Oct 3. About 1 year in 10, it comes as early as Sep 21. A 36°F night (frost possible on plants) typically shows up around Sep 25.
What growing zone is Parker, Colorado?
Zone 5b–6a. Most of Parker was 5b on the 2012 map too, but 1 of 3 city ZIPs changed zone.
Is it too early to plant in Parker?
If it's before May 9, it's too early for frost-tender plants: another 32°F night is more likely than not. From May 9 to May 23, the risk falls from 50% to 10%. Cool-season crops such as peas and lettuce can be planted 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 Parker, the first 36°F night (frost possible on plants) typically comes around Sep 25, before the first 32°F night (Oct 3).
Download & sources
- Add Parker 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 USC00056323); 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.