USDA hardiness zone 3a
In zone 3a, the average annual extreme minimum temperature is -40 to -35°F (-40.0 to -37.2°C), based on 1991–2020 data from the 2023 USDA Plant Hardiness Zone Map.
What zone 3a means for your garden
A plant labeled "hardy to zone 3a" should survive a typical winter low of -40°F. Only very cold-hardy perennials survive; look for plants rated to this zone or colder, and use season-extension for vegetables. Zone 3b is the warmer half of zone 3.
ZIP codes in zone 3a: 18 in Alaska, 5 in contiguous U.S.. New to zones? Read how to read your hardiness zone.
Frost dates in zone 3a
No major city on this site is in zone 3a. Typical 30%-risk frost dates (estimate from 3 NOAA stations): last spring frost around Jun 4, first fall frost around Sep 6. Treat these as rough estimates — local frost dates vary a lot with elevation.
Estimated planting calendar for zone 3a
Based on the estimated frost dates above.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato Short season (94 frost-free days): choose early varieties. | Apr 9 – Apr 23 | Jun 11 – Jun 25 | — | — |
| Pepper Short season (94 frost-free days): choose early varieties. | Mar 26 – Apr 9 | Jun 18 – Jul 2 | — | — |
| Lettuce | Apr 23 – May 7 | May 21 – Jun 11 | May 7 – Jun 18 | — |
| Green Beans | — | — | Jun 11 – Jul 16 | — |
| Sweet Corn Short season (94 frost-free days): choose early varieties. | — | — | Jun 11 – Jul 9 | — |
| Zucchini & Summer Squash | May 7 – May 14 | Jun 11 – Jun 25 | Jun 11 – Jul 2 | — |
| Cucumber Short season (94 frost-free days): choose early varieties. | May 7 – May 14 | Jun 18 – Jun 25 | Jun 11 – Jul 2 | — |
| Carrot | — | — | May 14 – Jun 18 | — |
| Onion | Mar 12 – Mar 26 | May 7 – May 21 | — | — |
| Potato | — | May 7 – May 28 | — | — |
| Basil Short season (94 frost-free days): choose early varieties. | Apr 23 – May 7 | Jun 18 – Jul 2 | Jun 18 – Jul 9 | — |
| Spinach | — | — | Apr 23 – May 21 | Jul 12 – Aug 9 |
| Kale | Apr 9 – Apr 23 | May 7 – May 28 | May 7 – May 28 | — |
| Broccoli | Apr 9 – Apr 23 | May 21 – Jun 11 | — | — |
| Peas | — | — | Apr 23 – May 14 | — |
| Eggplant Short season (94 frost-free days): choose early varieties. | Mar 26 – Apr 9 | Jun 18 – Jul 2 | — | — |
| Cabbage | Apr 9 – Apr 23 | May 7 – May 21 | — | — |
| Radish | — | — | Apr 30 – Jun 18 | Jul 26 – Aug 23 |
| Strawberry | — | May 7 – May 28 | — | — |
| Beets | — | — | May 14 – Jun 25 | — |
Where zone 3a occurs
None of the 512 major cities on this site sits in zone 3a. It occurs mostly in thinly populated areas (ZIP codes: 18 in Alaska, 5 in contiguous U.S.).
← Zone 2b · Zone 3b → · All zones
Zone 3a questions
How cold does it get in zone 3a?
Zone 3a is defined by an average annual extreme minimum temperature of -40 to -35°F (-40.0 to -37.2°C) for 1991–2020 — the average of each year's single coldest night, not the record low. Individual winters can be colder, so plants rated exactly for zone 3a carry some risk in a severe year.
When is the last frost in zone 3a?
Roughly Jun 4 for spring and Sep 6 for the first fall frost (estimate from 3 NOAA stations). Treat these as rough: frost dates swing widely with elevation.
Which states have zone 3a?
The 2023 listings put 23 ZIP codes in zone 3a, spread over 2 states and territories. The most are in Alaska (18), Minnesota (5).
Did zone 3a grow on the 2023 map?
No: 56 ZIP codes were in zone 3a on the 2012 map and 23 are on the 2023 map (-33). Of today's zone 3a ZIP codes that were also listed in 2012, 48% were in a colder zone then, 43% were already 3a, and 9% were in a warmer zone. What changed in 2023.