Tonto Basin, AZ planting calendar
- USDA zone
- 9a20 to 25 °F
- Last frost
- Mar 7avg, 32°F
- First frost
- Nov 20avg, 32°F
- Growing season
- 255days
Tonto Basin, Arizona is in USDA plant hardiness zone 9a. Its average last spring frost is around March 7 and the first fall frost around November 20, giving a growing season of about 255 days (NOAA 1991–2020 normals, 32°F, median). Start tender crops like tomatoes and peppers indoors weeks before the last frost and set them out afterward; sow hardy crops such as peas, spinach, and lettuce before it. The planner below turns those frost dates into a printable per-crop planting calendar.
Tonto Basin planting calendar
Each crop's windows are counted from Tonto Basin's average frost dates. 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.
- Start indoors
- Plant out
- Fall sowing
- First harvest
| Crop | Frost tolerance | Start indoors | Plant out | First harvest | Fall planting |
|---|---|---|---|---|---|
| Tomato | Tender | Jan 10 – Jan 24 | Mar 14 – Mar 21 | May 13 – Jun 2 | — |
| Pepper | Very tender | Jan 1 – Jan 10 | Mar 21 – Mar 28 | May 20 – Jun 19 | — |
| Cucumber | Tender | Feb 7 – Feb 14 | Mar 14 – Mar 21 | May 3 – May 23 | — |
| Summer squash / zucchini | Tender | — | Mar 14 – Mar 21 | Apr 28 – May 13 | — |
| Bush bean | Tender | — | Mar 14 – Mar 21 | May 3 – May 13 | Sep 21 – Oct 1 |
| Sweet corn | Tender | — | Mar 7 – Mar 21 | May 6 – Jun 5 | — |
| Basil | Very tender | Jan 24 – Feb 7 | Mar 14 – Mar 21 | Apr 13 – Apr 28 | — |
| Lettuce | Half-hardy | Jan 24 – Feb 7 | Feb 7 – Feb 21 | Mar 24 – Apr 8 | Sep 7 – Sep 22 |
| Pea | Hardy | — | Jan 24 – Feb 7 | Mar 20 – Apr 4 | Aug 28 – Sep 12 |
| Spinach | Hardy | — | Jan 24 – Feb 7 | Mar 5 – Mar 15 | Sep 17 – Sep 27 |
| Carrot | Half-hardy | — | Feb 14 – Feb 21 | Apr 15 – May 5 | Aug 18 – Sep 7 |
| Broccoli | Half-hardy | Jan 10 – Jan 24 | Feb 7 – Feb 21 | Apr 3 – Apr 23 | Aug 23 – Sep 12 |
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.
Frost & freeze dates
From NOAA's 1991–2020 Climate Normals at station USC00026840. 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 (p10 for spring, p90 for fall) — 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 | Mar 27 | Apr 16 | Nov 10 | Nov 22 | 224 |
| 32°F (freeze) | Mar 7 | Mar 27 | Nov 20 | Dec 3 | 255 |
| 28°F | Feb 15 | Mar 7 | Dec 1 | Dec 17 | 286 |
| 24°F | Jan 26 | Feb 21 | Dec 15 | Jan 5 | 323 |
32°F is the standard "freeze" line that damages tender crops; lighter 36°F frost can nip the most cold-sensitive plants, while hardy crops shrug off light frost down toward 28°F. Use the threshold that matches what you are protecting.
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. Warm-season crops need a long, warm GDD total; a short, cool GDD total favors greens and brassicas.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 6,341 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 9,651 | cool-season crops (brassicas, greens) |
Hardiness zone 9a
Tonto Basin sits in USDA plant hardiness zone 9a on the 2023 map — meaning its average annual extreme minimum winter temperature is about 20 to 25 °F. That number 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.
Explore more places in zone 9a, or see all USDA hardiness zones.
Frequently asked questions
- What USDA hardiness zone is Tonto Basin?
- Tonto Basin, Arizona is in USDA plant hardiness zone 9a on the 2023 map (average annual extreme minimum temperature 20 to 25 °F) — from the USDA Plant Hardiness Zone Map 2023, matched to this location's ZIP. See the methodology page for sources.
- When is the last frost in Tonto Basin?
- The average (median) last spring frost at 32°F is around March 7, from NOAA's 1991–2020 climate normals at the nearest reporting station. Roughly one year in ten the last frost is as late as March 27, so wait until then before setting out frost-tender plants if you want to be safe.
- When is the first fall frost in Tonto Basin?
- The average first fall frost at 32°F is around November 20. That leaves a growing season of about 255 days between the average last spring and first fall frosts.
- When should I start tomatoes in Tonto Basin?
- Start tomato seeds indoors about Jan 10 – Jan 24 and transplant them outside about Mar 14 – Mar 21, once the danger of frost has passed. Estimated first harvest is around May 13 – Jun 2.
- How long is the growing season in Tonto Basin?
- About 255 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~March 7) and the average first fall frost (~November 20). Cold-hardy crops extend usable time at both ends; frost-tender crops fit inside it.
Sources & method
Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020 for station USC00026840 (Punkin Ctr, 10.3 km away). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to this 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.