USDA zone 6a in Arizona
USDA plant hardiness zone 6a covers 5 locations across Arizona (average annual extreme minimum −10 to −5 °F): Flagstaff, AZ, Fort Valley, AZ, Ganado, AZ, Greer, AZ, Greer, AZ. Average last spring frost across this group ranges May 15 (Ganado) to June 11 (Fort Valley), and growing seasons run 99–147 days (Fort Valley to Ganado) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Arizona location's own frost dates; the printable planting calendar uses Greer, this group's median-season location.
- USDA zone
- 6a−10 to −5 °F
- Last frost range
- May 15–Jun 11avg, 32°F
- First frost range
- Sep 25–Oct 10avg, 32°F
- Growing season range
- 99–147days
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) |
|---|---|---|---|---|---|
| Flagstaff | Mountainaire | Flagstaff Pulliam Ap | Jun 4 | Sep 28 | 115 |
| Fort Valley | — | Ft Valley | Jun 11 | Sep 25 | 99 |
| Ganado | — | Ganado | May 15 | Oct 10 | 147 |
| Greer * | — | Springerville | Jun 1 | Sep 26 | 114 |
| Greer | — | Greer | Jun 5 | Sep 29 | 113 |
* Greer 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 (Greer, representative)
Computed from Greer's average frost dates — the median-season location in this Arizonazone 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 | Apr 6 – Apr 20 | Jun 8 – Jun 15 | Aug 7 – Aug 27 | — | matures comfortably |
| Pepper | Very tender | Mar 23 – Apr 6 | Jun 15 – Jun 22 | Aug 14 – Sep 13 | — | matures, but with little margin |
| Cucumber | Tender | May 4 – May 11 | Jun 8 – Jun 15 | Jul 28 – Aug 17 | — | matures comfortably |
| Summer squash / zucchini | Tender | — | Jun 8 – Jun 15 | Jul 23 – Aug 7 | — | matures comfortably |
| Bush bean | Tender | — | Jun 8 – Jun 15 | Jul 28 – Aug 7 | Jul 28 – Aug 7 | matures comfortably |
| Sweet corn | Tender | — | Jun 1 – Jun 15 | Jul 31 – Aug 30 | — | matures comfortably |
| Basil | Very tender | Apr 20 – May 4 | Jun 8 – Jun 15 | Jul 8 – Jul 23 | — | matures comfortably |
| Lettuce | Half-hardy | Apr 20 – May 4 | May 4 – May 18 | Jun 18 – Jul 3 | Jul 14 – Jul 29 | matures comfortably |
| Pea | Hardy | — | Apr 20 – May 4 | Jun 14 – Jun 29 | Jul 4 – Jul 19 | matures comfortably |
| Spinach | Hardy | — | Apr 20 – May 4 | May 30 – Jun 9 | Jul 24 – Aug 3 | matures comfortably |
| Carrot | Half-hardy | — | May 11 – May 18 | Jul 10 – Jul 30 | Jun 24 – Jul 14 | matures comfortably |
| Broccoli | Half-hardy | Apr 6 – Apr 20 | May 4 – May 18 | Jun 28 – Jul 18 | Jun 29 – Jul 19 | matures comfortably |
Which crops fit this growing season
Using Greer's own 114-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 11 of 12 crops mature here with comfortable margin, 1matures with little room to spare. The tightest fits: pepper (+13 day 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 (Greer)
From NOAA's 1991–2020 Climate Normals at station USC00028162. 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 12 | Jun 30 | Sep 18 | Sep 30 | 93 |
| 32°F (freeze) | Jun 1 | Jun 20 | Sep 26 | Oct 7 | 114 |
| 28°F | May 18 | Jun 6 | Oct 3 | Oct 17 | 135 |
| 24°F | May 6 | May 23 | Oct 11 | Oct 26 | 156 |
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 5 locations is 1,730; Greer's own reading is shown below.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 2,249 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 4,498 | cool-season crops (brassicas, greens) |
Hardiness zone 6a in Arizona
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. Arizona spans 10 hardiness zones in this dataset — see all Arizona locations for the full range, including zones5b, 6b, 7a, 7b, 8a, 8b, 9a, 9b, 10a.
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 Arizona?
- Zone 6a means an average annual extreme minimum winter temperature of −10 to −5 °F — the standard USDA measure of which perennials survive winter. 5 locations in Arizona fall in this zone. It does not set planting dates; see the frost calendar below for that.
- Where in Arizona's zone 6a is the growing season longest?
- Ganado runs the longest season on this page at about 147 days; Fort Valley is shortest at about 99 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 Arizona's zone 6a?
- Using Greer's frost dates (this page's median-season location): start seeds indoors about Apr 6 – Apr 20, then transplant outside about Jun 8 – Jun 15. 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 Arizona'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 5 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.