Circle, AK planting calendar
- USDA zone
- 1a−60 to −55 °F
- Last frost
- May 25avg, 32°F
- First frost
- Aug 26avg, 32°F
- Growing season
- 92days
Circle, Alaska is in USDA plant hardiness zone 1a. Its average last spring frost is around May 25 and the first fall frost around August 26, giving a growing season of about 92 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.
Circle planting calendar
Each crop's windows are counted from Circle'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 | Mar 30 – Apr 13 | Jun 1 – Jun 8 | Jul 31 – Aug 20 | — |
| Pepper | Very tender | Mar 16 – Mar 30 | Jun 8 – Jun 15 | Aug 7 – Sep 6 | — |
| Cucumber | Tender | Apr 27 – May 4 | Jun 1 – Jun 8 | Jul 21 – Aug 10 | — |
| Summer squash / zucchini | Tender | — | Jun 1 – Jun 8 | Jul 16 – Jul 31 | — |
| Bush bean | Tender | — | Jun 1 – Jun 8 | Jul 21 – Jul 31 | Jun 27 – Jul 7 |
| Sweet corn | Tender | — | May 25 – Jun 8 | Jul 24 – Aug 23 | — |
| Basil | Very tender | Apr 13 – Apr 27 | Jun 1 – Jun 8 | Jul 1 – Jul 16 | — |
| Lettuce | Half-hardy | Apr 13 – Apr 27 | Apr 27 – May 11 | Jun 11 – Jun 26 | Jun 13 – Jun 28 |
| Pea | Hardy | — | Apr 13 – Apr 27 | Jun 7 – Jun 22 | Jun 3 – Jun 18 |
| Spinach | Hardy | — | Apr 13 – Apr 27 | May 23 – Jun 2 | Jun 23 – Jul 3 |
| Carrot | Half-hardy | — | May 4 – May 11 | Jul 3 – Jul 23 | May 24 – Jun 13 |
| Broccoli | Half-hardy | Mar 30 – Apr 13 | Apr 27 – May 11 | Jun 21 – Jul 11 | May 29 – Jun 18 |
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 USC00501466. 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 | — | — | — | — | 66 |
| 32°F (freeze) | May 25 | Jun 6 | Aug 26 | Sep 7 | 92 |
| 28°F | May 14 | May 28 | Sep 5 | Sep 18 | 113 |
| 24°F | May 7 | May 20 | Sep 16 | Sep 28 | 131 |
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) | 859 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 2,060 | cool-season crops (brassicas, greens) |
Hardiness zone 1a
Circle sits in USDA plant hardiness zone 1a on the 2023 map — meaning its average annual extreme minimum winter temperature is about −60 to −55 °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 1a, or see all USDA hardiness zones.
Frequently asked questions
- What USDA hardiness zone is Circle?
- Circle, Alaska is in USDA plant hardiness zone 1a on the 2023 map (average annual extreme minimum temperature −60 to −55 °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 Circle?
- The average (median) last spring frost at 32°F is around May 25, 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 6, so wait until then before setting out frost-tender plants if you want to be safe.
- When is the first fall frost in Circle?
- The average first fall frost at 32°F is around August 26. That leaves a growing season of about 92 days between the average last spring and first fall frosts.
- When should I start tomatoes in Circle?
- Start tomato seeds indoors about Mar 30 – Apr 13 and transplant them outside about Jun 1 – Jun 8, once the danger of frost has passed. Estimated first harvest is around Jul 31 – Aug 20.
- How long is the growing season in Circle?
- About 92 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~May 25) and the average first fall frost (~August 26). 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 USC00501466 (Central #2, 40.5 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.