USDA hardiness zone 6a
In zone 6a, the average annual extreme minimum temperature is -10 to -5°F (-23.3 to -20.6°C), based on 1991–2020 data from the 2023 USDA Plant Hardiness Zone Map.
What zone 6a means for your garden
A plant labeled "hardy to zone 6a" should survive a typical winter low of -10°F. Most perennials sold at garden centers are rated for this zone or colder; marginal plants rated one zone warmer can survive in sheltered spots. Zone 6b is the warmer half of zone 6.
ZIP codes in zone 6a: 5,183 in contiguous U.S., 4 in Alaska. New to zones? Read how to read your hardiness zone.
Frost dates in zone 6a
Across 44 major cities in zone 6a, the 30%-risk last spring frost ranges from Apr 17 to Jun 10 (median May 4), and the first fall frost has a median of Oct 9. Frost timing depends on elevation, latitude and distance from water — a zone does not set a frost date, so check your city page for local dates.
Typical planting calendar for zone 6a
Based on the median frost dates above. For your exact dates, use your city page.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato | Mar 9 – Mar 23 | May 11 – May 25 | — | — |
| Pepper | Feb 23 – Mar 9 | May 18 – Jun 1 | — | — |
| Lettuce | Mar 23 – Apr 6 | Apr 20 – May 11 | Apr 6 – May 18 | Jul 31 – Aug 28 |
| Green Beans | — | — | May 11 – Jun 15 | Jul 17 – Jul 31 |
| Sweet Corn | — | — | May 11 – Jun 8 | — |
| Zucchini & Summer Squash | Apr 6 – Apr 13 | May 11 – May 25 | May 11 – Jun 1 | Jul 17 – Jul 31 |
| Cucumber | Apr 6 – Apr 13 | May 18 – May 25 | May 11 – Jun 1 | Jul 17 – Jul 31 |
| Carrot | — | — | Apr 13 – May 18 | Jul 17 – Jul 31 |
| Onion | Feb 9 – Feb 23 | Apr 6 – Apr 20 | — | — |
| Potato | — | Apr 6 – Apr 27 | — | — |
| Basil | Mar 23 – Apr 6 | May 18 – Jun 1 | May 18 – Jun 8 | — |
| Spinach | — | — | Mar 23 – Apr 20 | Aug 14 – Sep 11 |
| Kale | Mar 9 – Mar 23 | Apr 6 – Apr 27 | Apr 6 – Apr 27 | Jul 31 – Aug 28 |
| Broccoli | Mar 9 – Mar 23 | Apr 20 – May 11 | — | Jul 17 – Jul 31 |
| Peas | — | — | Mar 23 – Apr 13 | Jul 31 – Aug 14 |
| Eggplant | Feb 23 – Mar 9 | May 18 – Jun 1 | — | — |
| Cabbage | Mar 9 – Mar 23 | Apr 6 – Apr 20 | — | Jul 17 – Jul 31 |
| Radish | — | — | Mar 30 – May 18 | Aug 28 – Sep 25 |
| Strawberry | — | Apr 6 – Apr 27 | — | — |
| Beets | — | — | Apr 13 – May 25 | Jul 31 – Aug 14 |
Cities in zone 6a (44)
Major cities whose center falls in zone 6a:
- Chicago, IL — last frost Apr 17, first frost Nov 1
- Denver, CO — last frost May 8, first frost Oct 3
- Milwaukee, WI — last frost May 2, first frost Oct 12
- Colorado Springs, CO — last frost May 8, first frost Oct 3
- Omaha, NE — last frost Apr 25, first frost Oct 12
- Aurora, CO — last frost May 12, first frost Oct 2
- Lincoln, NE — last frost Apr 30, first frost Oct 7
- Fort Wayne, IN — last frost May 1, first frost Oct 16
- Worcester, MA — last frost May 6, first frost Oct 4
- Grand Rapids, MI — last frost May 4, first frost Oct 13
- Lakewood, CO — last frost May 8, first frost Oct 2
- Springfield, MA — last frost May 9, first frost Oct 3
- Joliet, IL — last frost Apr 26, first frost Oct 20
- Thornton, CO — last frost May 7, first frost Oct 4
- Syracuse, NY — last frost May 5, first frost Oct 11
- Ann Arbor, MI — last frost May 11, first frost Oct 4
- Arvada, CO — last frost May 11, first frost Sep 29
- Manchester, NH — last frost May 4, first frost Oct 6
- Westminster, CO — last frost May 7, first frost Oct 4
- Lansing, MI — last frost May 7, first frost Oct 6
- Springfield, IL — last frost Apr 20, first frost Oct 17
- Peoria, IL — last frost Apr 23, first frost Oct 18
- Pueblo, CO — last frost May 4, first frost Oct 4
- Centennial, CO — last frost May 10, first frost Oct 3
- Boulder, CO — last frost May 11, first frost Sep 30
- Fishers, IN — last frost Apr 28, first frost Oct 15
- South Bend, IN — last frost May 7, first frost Oct 14
- Carmel, IN — last frost Apr 28, first frost Oct 15
- Albany, NY — last frost May 2, first frost Oct 9
- Champaign, IL — last frost Apr 21, first frost Oct 19
- Nashua, NH — last frost May 4, first frost Oct 5
- Waukegan, IL — last frost May 4, first frost Oct 12
- Farmington Hills, MI — last frost May 8, first frost Oct 10
- Cicero, IL — last frost Apr 17, first frost Oct 26
- Flint, MI — last frost May 10, first frost Oct 7
- Bloomington, IL — last frost May 1, first frost Oct 11
- Wyoming, MI — last frost May 4, first frost Oct 13
- Rochester Hills, MI — last frost May 2, first frost Oct 16
- Broomfield, CO — last frost May 7, first frost Oct 4
- Racine, WI — last frost Apr 27, first frost Oct 18
- Flagstaff, AZ — last frost Jun 10, first frost Sep 23
- Hammond, IN — last frost Apr 30, first frost Oct 15
- Evanston, IL — last frost May 2, first frost Oct 14
- Portland, ME — last frost May 1, first frost Oct 9
← Zone 5b · Zone 6b → · All zones
Zone 6a questions
How cold does it get in zone 6a?
Zone 6a is defined by an average annual extreme minimum temperature of -10 to -5°F (-23.3 to -20.6°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 6a carry some risk in a severe year.
When is the last frost in zone 6a?
It depends far more on the city than on the zone. Among 44 zone 6a cities on this site, the 30%-risk last spring frost runs from Apr 17 in Chicago, IL to Jun 10 in Flagstaff, AZ — 54 days apart (median May 4).
Which states have zone 6a?
The 2023 listings put 5,187 ZIP codes in zone 6a, spread over 30 states and territories. The most are in Illinois (646), Michigan (640), Indiana (567), Ohio (544), Pennsylvania (510).
Did zone 6a grow on the 2023 map?
No: 5,858 ZIP codes were in zone 6a on the 2012 map and 5,187 are on the 2023 map (-671). Of today's zone 6a ZIP codes that were also listed in 2012, 56% were in a colder zone then, 44% were already 6a, and 1% were in a warmer zone. What changed in 2023.
Which big cities are in zone 6a?
The largest cities on this site in zone 6a are Chicago, IL, Denver, CO, Milwaukee, WI; 44 cities in all are listed below.