USDA zone 6a in Utah
USDA plant hardiness zone 6a covers 50 locations across Utah (average annual extreme minimum −10 to −5 °F): Alpine, UT, Alta, UT, Altamont, UT, Alton, UT, Amalga, UT, Beaver, UT, and 44 more. Average last spring frost across this group ranges April 18 (Teasdale) to June 21 (Brian Head), and growing seasons run 82–192 days (Brian Head to Teasdale) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Utah location's own frost dates; the printable planting calendar uses Castle Dale, this group's median-season location.
- USDA zone
- 6a−10 to −5 °F
- Last frost range
- Apr 18–Jun 21avg, 32°F
- First frost range
- Sep 12–Oct 28avg, 32°F
- Growing season range
- 82–192days
Locations in this group
Every location below shares this zone and a nearby weather station, but keeps its own frost dates — find your town for its own numbers, or use the ZIP planner on the home page for an instant personalized answer.
| Location | Also covers | Nearest station | Last frost | First frost | Season (days) |
|---|---|---|---|---|---|
| Alpine | — | Alpine | May 3 | Oct 12 | 159 |
| Alta | — | Alta | Jun 11 | Sep 18 | 98 |
| Altamont | Tabiona | Altamont | May 31 | Sep 23 | 112 |
| Alton | — | Alton | Jun 1 | Sep 30 | 120 |
| Amalga | Mendon | Logan Radio Kvnu | May 8 | Oct 2 | 145 |
| Beaver | — | Beaver Canyon Pwr House | Jun 1 | Sep 28 | 120 |
| Beaver | Minersville, Milford | Milford Muni Ap | May 13 | Oct 4 | 143 |
| Brian Head | — | Brian Head | Jun 21 | Sep 12 | 82 |
| Castle Dale * | Huntington, Orangeville, Cleveland | Castle Dale | May 18 | Sep 27 | 128 |
| Cedar Fort | — | Fairfield | Jun 2 | Sep 16 | 103 |
| Clawson | — | Ferron | May 6 | Oct 10 | 156 |
| Duchesne | Tabiona | Duchesne | May 6 | Oct 5 | 150 |
| East Carbon | Wellington, Elmo | Price Carbon Co Ap | May 3 | Oct 12 | 160 |
| Ephraim | — | Ephraim | May 28 | Sep 20 | 113 |
| Fillmore | — | Fillmore | May 4 | Oct 14 | 160 |
| Fremont | Bicknell | Loa | May 31 | Sep 21 | 112 |
| Gunnison | Manti, Centerfield, Redmond, Mayfield, Sterling | Manti | May 11 | Oct 6 | 146 |
| Helper | — | Scofield-skyline Mine | Jun 13 | Sep 17 | 94 |
| Henefer | Echo | Echo Dam | May 30 | Sep 18 | 112 |
| Howell | — | Thiokol Propulsion F S | May 17 | Sep 24 | 128 |
| Huntsville | — | Huntsville Monastery | Jun 4 | Sep 16 | 102 |
| Independence | Midway | Heber | Jun 4 | Sep 20 | 106 |
| Joseph | — | Fremont Indian Sp | Jun 4 | Sep 21 | 106 |
| Koosharem | — | Koosharem | Jun 6 | Sep 21 | 104 |
| Levan | — | Levan | May 10 | Oct 7 | 148 |
| Lewiston | Cornish, Richmond | Richmond | May 11 | Oct 5 | 143 |
| Liberty | — | Pineview Dam | May 22 | Sep 26 | 125 |
| Logan | North Logan, Avon, Hyde Park, Providence | Logan Utah St Univ | Apr 30 | Oct 16 | 166 |
| Lynndyl | Leamington | Oak City | May 2 | Oct 13 | 162 |
| Mantua | — | Brigham City Waste Plt | May 5 | Oct 5 | 150 |
| Mapleton | — | Spanish Fk Pwr House | Apr 25 | Oct 18 | 174 |
| Marysvale | Junction | Marysvale | May 24 | Sep 25 | 123 |
| Monroe | Elsinore, Sigurd, Aurora, Koosharem, Annabella, Glenwood | Richfield Radio Ksvc | May 21 | Sep 24 | 125 |
| Morgan | — | Morgan | May 25 | Sep 24 | 119 |
| Neola | Whiterocks | Neola | May 19 | Sep 29 | 130 |
| Nephi | — | Nephi | May 6 | Oct 10 | 156 |
| Panguitch | Hatch, Paragonah | Panguitch | Jun 12 | Sep 12 | 90 |
| Park | — | Park City | May 29 | Sep 25 | 117 |
| Parowan | — | Cedar City 5e | May 23 | Oct 4 | 130 |
| Peter | Cache, Portage, Clarkston, Plymouth, Newton, Fielding | Cutler Dam | May 3 | Oct 12 | 160 |
| Redmond | Holden | Scipio | May 22 | Sep 25 | 122 |
| Rush Valley | — | Johnson Pass | May 15 | Oct 5 | 142 |
| Salina | — | Salina 24 E | May 29 | Sep 26 | 118 |
| Snowville | Malta | Rosette | May 21 | Oct 2 | 132 |
| Spring | — | Moroni | May 26 | Sep 25 | 119 |
| Sutherland | — | Deseret | May 14 | Sep 30 | 137 |
| Teasdale | — | Capitol Reef Np | Apr 18 | Oct 28 | 192 |
| Tropic | Cannonville | Bryce Canyon Np Hqrs | May 23 | Sep 27 | 125 |
| Wallsburg | — | Deer Creek Dam | May 28 | Sep 23 | 119 |
| Wellsville | Avon, Millville | Logan 5 Sw Exp Farm | May 12 | Sep 28 | 138 |
* Castle Dale is this group's median-season location — the calendar below is computed from its data.
Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.
Planting calendar (Castle Dale, representative)
Computed from Castle Dale's average frost dates — the median-season location in this Utahzone 6a group. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees — your own location's dates may run a week or two earlier or later (see the table above).
- Start indoors
- Plant out
- Fall sowing
- First harvest
| Crop | Frost tolerance | Start indoors | Plant out | First harvest | Fall planting | Season fit |
|---|---|---|---|---|---|---|
| Tomato | Tender | Mar 23 – Apr 6 | May 25 – Jun 1 | Jul 24 – Aug 13 | — | matures comfortably |
| Pepper | Very tender | Mar 9 – Mar 23 | Jun 1 – Jun 8 | Jul 31 – Aug 30 | — | matures comfortably |
| Cucumber | Tender | Apr 20 – Apr 27 | May 25 – Jun 1 | Jul 14 – Aug 3 | — | matures comfortably |
| Summer squash / zucchini | Tender | — | May 25 – Jun 1 | Jul 9 – Jul 24 | — | matures comfortably |
| Bush bean | Tender | — | May 25 – Jun 1 | Jul 14 – Jul 24 | Jul 29 – Aug 8 | matures comfortably |
| Sweet corn | Tender | — | May 18 – Jun 1 | Jul 17 – Aug 16 | — | matures comfortably |
| Basil | Very tender | Apr 6 – Apr 20 | May 25 – Jun 1 | Jun 24 – Jul 9 | — | matures comfortably |
| Lettuce | Half-hardy | Apr 6 – Apr 20 | Apr 20 – May 4 | Jun 4 – Jun 19 | Jul 15 – Jul 30 | matures comfortably |
| Pea | Hardy | — | Apr 6 – Apr 20 | May 31 – Jun 15 | Jul 5 – Jul 20 | matures comfortably |
| Spinach | Hardy | — | Apr 6 – Apr 20 | May 16 – May 26 | Jul 25 – Aug 4 | matures comfortably |
| Carrot | Half-hardy | — | Apr 27 – May 4 | Jun 26 – Jul 16 | Jun 25 – Jul 15 | matures comfortably |
| Broccoli | Half-hardy | Mar 23 – Apr 6 | Apr 20 – May 4 | Jun 14 – Jul 4 | Jun 30 – Jul 20 | matures comfortably |
Which crops fit this growing season
Using Castle Dale's own 128-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 12 of 12 crops mature here with comfortable margin. A different location in the table above with a longer or shorter season will get a different mix — the ZIP planner on the home page gives your own.
Frost & freeze dates (Castle Dale)
From NOAA's 1991–2020 Climate Normals at station USC00421214. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 — the conservative date to plant after or harvest before.
| Threshold | Last spring — avg | Last spring — 90%-safe | First fall — avg | First fall — 90%-safe | Season (days) |
|---|---|---|---|---|---|
| 36°F | Jun 3 | Jun 19 | Sep 18 | Sep 28 | 105 |
| 32°F (freeze) | May 18 | Jun 8 | Sep 27 | Oct 9 | 128 |
| 28°F | May 4 | May 20 | Oct 5 | Oct 20 | 153 |
| 24°F | Apr 23 | May 6 | Oct 18 | Nov 1 | 175 |
Growing degree days
Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. This group's median GDD (base 50°F) across all 50 locations is 2,337; Castle Dale's own reading is shown below.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 2,574 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 4,673 | cool-season crops (brassicas, greens) |
Hardiness zone 6a in Utah
Zone 6a means an average annual extreme minimum winter temperature of about −10 to −5 °F on the USDA's 2023 map — the number that tells you which perennials, shrubs, and trees reliably survive an average winter here. It does not set your planting dates, which come from the frost calendar above. Utah spans 9 hardiness zones in this dataset — see all Utah locations for the full range, including zones4a, 5a, 5b, 6b, 7a, 7b, 8a, 8b.
Explore zone 6a in other states at zone 6a, or see all USDA hardiness zones.
Frequently asked questions
- What does USDA hardiness zone 6a mean in Utah?
- Zone 6a means an average annual extreme minimum winter temperature of −10 to −5 °F — the standard USDA measure of which perennials survive winter. 50 locations in Utah fall in this zone. It does not set planting dates; see the frost calendar below for that.
- Where in Utah's zone 6a is the growing season longest?
- Teasdale runs the longest season on this page at about 192 days; Brian Head is shortest at about 82 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.
- When should I plant tomatoes in Utah's zone 6a?
- Using Castle Dale's frost dates (this page's median-season location): start seeds indoors about Mar 23 – Apr 6, then transplant outside about May 25 – Jun 1. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.
- Does every location in Utah's zone 6a have the same frost dates?
- No — they do not all share a weather station, so frost dates vary by a week or more across the 50 locations listed (see the table above for each location's own dates).
Sources & method
Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020, one reading per location's own nearest station (see the table above). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to each location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.