Greeley, Colorado Frost Dates, Growing Season & Hardiness Zone
Frost odds and planting zone for Greeley 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 14 (10% risk)
earlyMay 2
typicalMay 14
safer
First fall frost
Oct 8
typical (50% chance it has happened by then)
Early-risk date: Sep 26 (10%)
Growing season
159 days
typical frost-free (32°F) season
Short year: 139 days (1 year in 10 is shorter)
USDA hardiness zone
5a–5b
2023 map: -20 to -10°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 May 2 at Greeley UNC and as late as May 12 at Waterdale.
Typical last freeze (32°F): May 2. In 1 year out of 10, the last one comes after May 14.
Based on NOAA station Greeley UNC (USC00053553), 3.9 mi ESE, elevation 4,715 ft (−157 ft vs. city center). Confidence: High.
When is the last frost in Greeley?
The typical last 32°F night is May 2, and in 1 year out of 10 a freeze still comes after May 14. 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 20.
The typical date (May 2) and the safer 1-in-10 date (May 14) are 12 days apart. If you plant in between, you're taking a chance; watch the 10-day forecast.
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.
Of the 6 eligible stations near Greeley, ours has the earliest typical last frost. In a colder pocket, plan closer to May 14.
| Threshold | 10% (safer) | 30% | 50% (typical) | 90% (early) |
|---|---|---|---|---|
| 36°F (frost possible on plants) | May 26 | May 17 | May 12 | May 1 |
| 32°F freeze | May 14 | May 7 | May 2 | Apr 17 |
| 28°F hard freeze | May 5 | Apr 27 | Apr 20 | Apr 5 |
All probabilities (10–90%)
| Threshold | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F (frost possible on plants) | May 26 | May 20 | May 17 | May 15 | May 12 | May 10 | May 8 | May 4 | May 1 |
| 32°F freeze | May 14 | May 10 | May 7 | May 5 | May 2 | Apr 30 | Apr 27 | Apr 22 | Apr 17 |
| 28°F hard freeze | May 5 | May 1 | Apr 27 | Apr 24 | Apr 20 | Apr 17 | Apr 14 | Apr 10 | Apr 5 |
Is it safe to plant after Mother's Day in Greeley?
Mother's Day is the usual planting signal for many gardeners around Greeley (CSU PlantTalk). In 2027 that's May 9. As of that date, NOAA 1991–2020 normals at Greeley UNC give between 20% and 30% odds of another 32°F night and between 60% and 70% odds of another 36°F night (frost possible on plants).
Is it too early to plant in Greeley?
Before May 2 the odds of another 32°F night are better than even; after May 14 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 Greeley?
Half of years get their first 32°F night by Oct 8. In 1 year out of 10, it arrives as early as Sep 26. The first 36°F night (frost possible on plants) typically comes around Sep 30, and the first 28°F hard freeze around Oct 18.
To time a fall crop, count back from the typical first frost (Oct 8) or the safer Sep 26. The planting calendar works it out crop by crop.
| Threshold | 10% (early) | 30% | 50% (typical) | 90% (late) |
|---|---|---|---|---|
| 36°F (frost possible on plants) | Sep 18 | Sep 25 | Sep 30 | Oct 11 |
| 32°F freeze | Sep 26 | Oct 3 | Oct 8 | Oct 21 |
| 28°F hard freeze | Oct 4 | Oct 12 | Oct 18 | Nov 1 |
All probabilities (10–90%)
| Threshold | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F (frost possible on plants) | Sep 18 | Sep 23 | Sep 25 | Sep 28 | Sep 30 | Oct 2 | Oct 4 | Oct 7 | Oct 11 |
| 32°F freeze | Sep 26 | Oct 1 | Oct 3 | Oct 5 | Oct 8 | Oct 11 | Oct 14 | Oct 17 | Oct 21 |
| 28°F hard freeze | Oct 4 | Oct 9 | Oct 12 | Oct 15 | Oct 18 | Oct 21 | Oct 24 | Oct 27 | Nov 1 |
How long is Greeley's growing season?
Greeley's frost-free season (32°F) typically runs 159 days. In about 1 year out of 10, it's shorter than 139 days.
That's enough time for most warm-season vegetables if they go in on time. Long-season crops do best started from transplants.
The station averages 3,210 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) | 156 days | 139 days | 121 days |
| 32°F freeze | 178 days | 159 days | 139 days |
| 28°F hard freeze | 200 days | 179 days | 158 days |
How does Greeley's season compare?
Of the 20 Colorado cities with frost dates on this site, Greeley has a typical frost-free season of 159 days, which is the 8th longest.
Among the 56 U.S. cities with frost dates on this site, the typical frost-free season here is longer than in 12 of them and shorter than in 43.
Growing degree days (base 50°F)
Annual normal: 3,210 GDD (NOAA flag R, 23 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 | 4 | 40 | 156 | 473 | 1,064 | 1,854 | 2,575 | 3,039 | 3,190 | 3,208 | 3,208 |
What growing zone is Greeley? (USDA 2023)
On the 2023 USDA map, Greeley is zone 5a–5b (-20 to -10°F average coldest winter night). On the 2012 map, most of the city was 5b. Of the 3 city ZIPs listed in both tables: 1 moved down half a zone and 2 stayed the same.
| ZIP | 2023 | 2012 | Change | Share of ZIP in Greeley |
|---|---|---|---|---|
| 80620 | 5b | 5b | unchanged | 0% |
| 80631 | 5a | 5b | -1 half zone (colder) | 16% |
| 80634 mostly in city | 5b | 5b | unchanged | 72% |
Other ZIPs touching Greeley and PO-box ZIPs
ZIPs outside the 806 prefix that overlap the city boundary:
- 80534: 2023 5b, 2012 5b (0.0% of the ZIP is in Greeley)
- 80543: 2023 5b, 2012 5b (9.5% of the ZIP is in Greeley)
- 80550: 2023 5b, 2012 5b (3.3% of the ZIP is in Greeley)
PO-box and single-address 806xx ZIPs have no Census area, so we cannot tell which city they serve: 80601 (5b/5b), 80602 (6a/5b), 80603 (5b/5b), 80610 (5a/5a), 80611 (5a/5a), 80612 (5b/5a), 80614 (n/a/5b), 80615 (5a/5b), 80621 (5b/5b), 80622 (5a/5a), 80623 (5a/5b), 80624 (5a/5a), 80632 (5a/5b), 80633 (5b/5b), 80638 (5b/5b), 80639 (n/a/5b), 80640 (5b/5b), 80642 (5b/5b), 80643 (5b/5a), 80644 (5a/5a), 80645 (5a/5b), 80646 (n/a/5b), 80648 (5a/5a), 80649 (5a/5a), 80650 (5b/5a), 80651 (5b/5b), 80652 (5b/5a), 80653 (5a/5a), 80654 (5a/5a) (2023/2012).
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 Greeley'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 Greeley 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 Greeley frost dates differ between websites?
You may see May 7 given as Greeley'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 2, the 50% (median) date.
The 'safer' date, May 14, is the 10%-risk date. A 32°F night after it happens in only about 1 year in 10.
You may also see May 12. 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 6 stations that meet our quality rules put the typical (50%) last 32°F frost anywhere from May 2 to May 12 (table below).
| Date | What it is (NOAA 1991–2020) |
|---|---|
| May 7 | 32°F last frost, 30% risk (a 'balanced' date) |
| May 12 | 36°F last cold night, 50% (frost possible on plants) |
| May 14 | 32°F last frost, 10% risk (the 'safer' date) |
| Apr 20 | 28°F last hard freeze, 50% |
| May 10 | 32°F last frost, 50%, at Loveland 2 N (nearest station with NOAA flag S) |
| Station | Distance | Elevation | Typical last frost |
|---|---|---|---|
| Greeley UNC used here | 3.9 mi ESE | 4,715 ft | May 2 |
| Fort Collins | 20.0 mi NW | 5,004 ft | May 2 |
| Fort Collins 4 E | 17.3 mi NW | 4,920 ft | May 3 |
| Longmont 2 ESE | 23.4 mi SW | 4,950 ft | May 7 |
| Loveland 2 N | 16.6 mi W | 5,080 ft | May 10 |
| Waterdale | 23.1 mi W | 5,230 ft | May 12 |
Which weather station is this based on?
- Station
- Greeley UNC (NOAA USC00053553, COOP)
- Distance
- 3.9 mi ESE of the city center
- Elevation
- 4,715 ft; city center 4,872 ft (USGS), difference −157 ft
- Record
- NOAA completeness flag S, 25 of 30 years (1991–2020)
- Confidence
- High (rule)
Confidence: High. At 3.9 miles from the city center and only 157 ft off in elevation, with frost statistics that meet our completeness rule (NOAA flag S, 25 of 30 years), this station is a close match.
| Station | ID | Distance | Elev. (Δ) | Last frost 50% | First frost 50% | Season 50% | NOAA flag / years |
|---|---|---|---|---|---|---|---|
| Greeley UNC | USC00053553 | 3.9 mi ESE | 4,715 ft (-157) | May 2 | Oct 8 | 159 d | S / 25 |
| Loveland 2 N | USC00055236 | 16.6 mi W | 5,080 ft (+208) | May 10 | Oct 1 | 142 d | S / 25 |
| Fort Collins 4 E | USC00053006 | 17.3 mi NW | 4,920 ft (+48) | May 3 | Oct 6 | 154 d | S / 29 |
| Fort Collins | USC00053005 | 20.0 mi NW | 5,004 ft (+132) | May 2 | Oct 7 | 157 d | S / 29 |
| Waterdale | USC00058839 | 23.1 mi W | 5,230 ft (+358) | May 12 | Oct 1 | 141 d | R / 23 |
| Longmont 2 ESE | USC00055116 | 23.4 mi SW | 4,950 ft (+78) | May 7 | Oct 5 | 151 d | R / 17 |
Other stations within 25 mi (not used)
- none
73 other NOAA normals stations within 40 km (mostly rain gauges) have no frost statistics.
Greeley planting dates at a glance
Balanced dates use the 30%-risk last-frost date as the anchor. The Greeley 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 22 – May 6 | Jun 10 | – |
| Peppers | Mar 26 – Apr 9 | May 21 | – |
| Potatoes | – | Apr 23 – May 7 | – |
| Onions (dry, from sets) | – | Apr 9–23 | – |
| Peas | – | Apr 9–23 | sow by Jul 21 |
| Lettuce (leaf) | – | Apr 9–23 | sow by Jul 26 |
| Carrots | – | Apr 23 – May 7 | sow by Jul 16 |
| Beans (snap) | – | May 7 | sow by Jul 12 |
| Summer squash | – | May 7 | sow by Jul 22 |
| Broccoli | Feb 19 – Mar 5 | Apr 9–23 | transplant by Jul 21 |
| Cabbage | Feb 19 – Mar 5 | Apr 9–23 | transplant by Jul 1 |
| Cauliflower | Mar 5–19 | Apr 23 – May 7 | – |
| Kohlrabi | – | Apr 9–23 | sow by Aug 5 |
| Green onions | – | Apr 9–23 | sow by Jul 26 |
| Radishes | – | Apr 9–23 | sow by Aug 25 |
| Spinach | – | Apr 9–23 | sow by Aug 15 |
| Turnips | – | Apr 9–23 | sow by Aug 5 |
| Beets | – | Apr 23 – May 7 | sow by Jul 26 |
| Swiss chard | – | Apr 23 – May 7 | sow by Jul 26 |
| Parsnips | – | Apr 23 – May 7 | – |
| Sweet corn | – | May 7 | – |
| Cucumbers | – | May 7 | sow by Jul 17 |
| Eggplant | Mar 19 – Apr 9 | May 21 | – |
| Cantaloupe | – | May 21 | – |
| Watermelon | – | May 21 | – |
| Winter squash | – | May 21 | – |
| Garlic | – | – | plant Oct 1–14 |
When to plant tomatoes in Greeley · Fall planting dates for Greeley
Frost dates near Greeley
| City | Distance | Last frost | First frost | Season | Zone 2023 |
|---|---|---|---|---|---|
| Loveland frost dates | 15 mi | May 10 | Oct 1 | 142 days | 5b |
| Fort Collins frost dates | 18 mi | May 2 | Oct 7 | 157 days | 5b |
| Longmont frost dates | 24 mi | May 7 | Oct 5 | 151 days | 5b–6a |
| Thornton frost dates | 35 mi | May 2 | Oct 11 | 160 days | 6a |
| Commerce City frost dates | 37 mi | May 3 | Oct 7 | 155 days | 5b |
| Boulder frost dates | 37 mi | May 6 | Oct 5 | 151 days | 6a |
Frequently asked questions
What is the average last frost date in Greeley?
May 2 is the median (50%) date for Greeley's last 32°F night, from NOAA 1991–2020 normals at Greeley UNC. To play it safe, use May 14: only about 1 year in 10 has a freeze after it.
When is the first frost in Greeley?
Expect the first 32°F night by Oct 8 in a typical year, and as early as Sep 26 in about 1 year out of 10. Cold 36°F nights (frost possible on plants) typically start around Sep 30.
What growing zone is Greeley, Colorado?
Zone 5a–5b. Most of Greeley was 5b on the 2012 map too, but 1 of 3 city ZIPs changed zone.
Is it too early to plant in Greeley?
If it's before May 2, it's too early for frost-tender plants: another 32°F night is more likely than not. From May 2 to May 14, 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 Greeley, the first 36°F night (frost possible on plants) typically comes around Sep 30, before the first 32°F night (Oct 8).
Download & sources
- Add Greeley 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 USC00053553); 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.