USDA hardiness zone 1a
In zone 1a, the average annual extreme minimum temperature is -60 to -55°F (-51.1 to -48.3°C), based on 1991–2020 data from the 2023 USDA Plant Hardiness Zone Map.
What zone 1a means for your garden
A plant labeled "hardy to zone 1a" should survive a typical winter low of -60°F. Only very cold-hardy perennials survive; look for plants rated to this zone or colder, and use season-extension for vegetables. Zone 1b is the warmer half of zone 1.
ZIP codes in zone 1a: 5 in Alaska.
Frost dates in zone 1a
No major city on this site is in zone 1a. Typical 30%-risk frost dates (estimate borrowed from zone 1b (no stations in 1a)): last spring frost around May 29, first fall frost around Aug 27. Treat these as rough estimates — local frost dates vary a lot with elevation.
Estimated planting calendar for zone 1a
Based on the estimated frost dates above.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato Short season (90 frost-free days): choose early varieties. | Apr 3 – Apr 17 | Jun 5 – Jun 19 | — | — |
| Pepper Short season (90 frost-free days): choose early varieties. | Mar 20 – Apr 3 | Jun 12 – Jun 26 | — | — |
| Lettuce | Apr 17 – May 1 | May 15 – Jun 5 | May 1 – Jun 12 | — |
| Green Beans | — | — | Jun 5 – Jul 10 | — |
| Sweet Corn Short season (90 frost-free days): choose early varieties. | — | — | Jun 5 – Jul 3 | — |
| Zucchini & Summer Squash | May 1 – May 8 | Jun 5 – Jun 19 | Jun 5 – Jun 26 | — |
| Cucumber Short season (90 frost-free days): choose early varieties. | May 1 – May 8 | Jun 12 – Jun 19 | Jun 5 – Jun 26 | — |
| Carrot | — | — | May 8 – Jun 12 | — |
| Onion | Mar 6 – Mar 20 | May 1 – May 15 | — | — |
| Potato | — | May 1 – May 22 | — | — |
| Basil Short season (90 frost-free days): choose early varieties. | Apr 17 – May 1 | Jun 12 – Jun 26 | Jun 12 – Jul 3 | — |
| Spinach | — | — | Apr 17 – May 15 | Jul 2 – Jul 30 |
| Kale | Apr 3 – Apr 17 | May 1 – May 22 | May 1 – May 22 | — |
| Broccoli | Apr 3 – Apr 17 | May 15 – Jun 5 | — | — |
| Peas | — | — | Apr 17 – May 8 | — |
| Eggplant Short season (90 frost-free days): choose early varieties. | Mar 20 – Apr 3 | Jun 12 – Jun 26 | — | — |
| Cabbage | Apr 3 – Apr 17 | May 1 – May 15 | — | — |
| Radish | — | — | Apr 24 – Jun 12 | Jul 16 – Aug 13 |
| Strawberry | — | May 1 – May 22 | — | — |
| Beets | — | — | May 8 – Jun 19 | — |
Where zone 1a occurs
None of the 512 major cities on this site sits in zone 1a. It occurs mostly in thinly populated areas (ZIP codes: 5 in Alaska).