Cantwell, AK planting calendar
- USDA zone
- 4a−30 to −25 °F
- Last frost
- Jun 6avg, 32°F
- First frost
- Aug 25avg, 32°F
- Growing season
- 77days
Cantwell, Alaska is in USDA plant hardiness zone 4a. Its average last spring frost is around June 6 and the first fall frost around August 25, giving a growing season of about 77 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.
Cantwell planting calendar
Each crop's windows are counted from Cantwell'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 | Apr 11 – Apr 25 | Jun 13 – Jun 20 | Aug 12 – Sep 1 | — |
| Pepper | Very tender | Mar 28 – Apr 11 | Jun 20 – Jun 27 | Aug 19 – Sep 18 | — |
| Cucumber | Tender | May 9 – May 16 | Jun 13 – Jun 20 | Aug 2 – Aug 22 | — |
| Summer squash / zucchini | Tender | — | Jun 13 – Jun 20 | Jul 28 – Aug 12 | — |
| Bush bean | Tender | — | Jun 13 – Jun 20 | Aug 2 – Aug 12 | Jun 26 – Jul 6 |
| Sweet corn | Tender | — | Jun 6 – Jun 20 | Aug 5 – Sep 4 | — |
| Basil | Very tender | Apr 25 – May 9 | Jun 13 – Jun 20 | Jul 13 – Jul 28 | — |
| Lettuce | Half-hardy | Apr 25 – May 9 | May 9 – May 23 | Jun 23 – Jul 8 | Jun 12 – Jun 27 |
| Pea | Hardy | — | Apr 25 – May 9 | Jun 19 – Jul 4 | Jun 2 – Jun 17 |
| Spinach | Hardy | — | Apr 25 – May 9 | Jun 4 – Jun 14 | Jun 22 – Jul 2 |
| Carrot | Half-hardy | — | May 16 – May 23 | Jul 15 – Aug 4 | May 23 – Jun 12 |
| Broccoli | Half-hardy | Apr 11 – Apr 25 | May 9 – May 23 | Jul 3 – Jul 23 | May 28 – Jun 17 |
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 USC00505778. 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 | — | — | — | — | 40 |
| 32°F (freeze) | Jun 6 | Jun 30 | Aug 25 | Sep 8 | 77 |
| 28°F | May 21 | Jun 4 | Sep 6 | Sep 22 | 106 |
| 24°F | May 10 | May 27 | Sep 18 | Oct 2 | 128 |
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) | 414 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 1,484 | cool-season crops (brassicas, greens) |
Hardiness zone 4a
Cantwell sits in USDA plant hardiness zone 4a on the 2023 map — meaning its average annual extreme minimum winter temperature is about −30 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 4a, or see all USDA hardiness zones.
Frequently asked questions
- What USDA hardiness zone is Cantwell?
- Cantwell, Alaska is in USDA plant hardiness zone 4a on the 2023 map (average annual extreme minimum temperature −30 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 Cantwell?
- The average (median) last spring frost at 32°F is around June 6, from NOAA's 1991–2020 climate normals at the nearest reporting station. Roughly one year in ten the last frost is as late as June 30, so wait until then before setting out frost-tender plants if you want to be safe.
- When is the first fall frost in Cantwell?
- The average first fall frost at 32°F is around August 25. That leaves a growing season of about 77 days between the average last spring and first fall frosts.
- When should I start tomatoes in Cantwell?
- Start tomato seeds indoors about Apr 11 – Apr 25 and transplant them outside about Jun 13 – Jun 20, once the danger of frost has passed. Estimated first harvest is around Aug 12 – Sep 1.
- How long is the growing season in Cantwell?
- About 77 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~June 6) and the average first fall frost (~August 25). 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 USC00505778 (Mckinley Park, 72.1 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.